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Memories of Another day

Memories of Another day
While my Parents Pulin babu and Basanti devi were living

Sunday, November 22, 2009

Darwin’s Sacred Cause

Darwin's Sacred Cause


Indian Holcaust My Father`s Life and Time- Two Hundred EIGHTEEN

Palash Biswas


http://indianholocaustmyfatherslifeandtime.blogspot.com/



I am very happy to invent that a real Genious like Charles Darwin had to bear a family legacy which drove him to the Destinationof Evolution!His Hatred for Slavery made all the Difference! I may understand well the Motivation behind. Should we not be able ever to get Inspiration from this? Perhaps NO as a man like Ambedkar and his theory, the Ambedkar Ideology failed in India as we enlightened people suffer fromAcute Dementia and know Never the Dreams of our Ancestors so we might mobilised, awakened and organised ourselves for the Change. Black Untouchable Brotherhood should be obliged to some one like Charles darwin who NULLIFIED the basic Concept of Racial hatred and Discrimination that God has created the Negroids as per as the Animals. God has Created Nothing, Charle darwin Proved it long before. But the Aboriginal Indigenous Negroid Black Untouchables have not recovered from the Zionist GOD Phobia!

My Ftaher knew the Discrimination. he was not religious. But at the same time, he was Never an Atheist as my CHHOTOKAKA , Me and my Son happen to be. My father was not any Charles darwin nor me. But My father was against the Slavery as Charles darwin should have been. More over , he loved his People. He often used to say,` I must Stand Up to raise my voice to voice my Community! If I do not, who wouldthen?' We Never understood. But our people have the ROOTS in Folkand our Family Bondage is stronger than that of Ruling Class. Charles Darwin`s theory of Evolution denied the very existance of God who created us on this earth and ultimately it strengthened the forces which fought against Slavery. Darwin`s grand Fathers were involved in Anti Slavery Movement which Created a Charles Darwin. Our Fore Ftahers did lead so many Insurrections, Revolts and uprisings and laid their Lives! But we have no Charles Darwin!

150 years since 'The Origin of Species'

Ohio State University professor visits UT to discuss the life and work of Charles Darwin

By Vincent D. Scebbi

Published: Thursday, November 19, 2009

Updated: Thursday, November 19, 2009



On the eve of the 150th anniversary of the first publication of "The Origin of Species," Tim Berra, professor emeritus of evolution, ecology and organism biology at Ohio State University, spoke about the life of Charles Darwin.

Berra visited UT to give his award-winning presentation, "Charles Darwin: The Story of an Extraordinary Man" on Tuesday.

"The theory of evolution is arguably the greatest idea ever had by the human mind and Charles Darwin is arguably one of the most influential scientists ever. He changed the way humans see themselves in nature," Berra said.

According to Berra, "The Origin of Species" was first published on Nov. 24, 1859, which marked the beginning of modern biology.

Berra said Darwin linked two observations together to form his theory of evolution.

The first observation was that there are variations in nature. The second was more offspring are produced than those who survive.

"Therefore, there is a struggle for existence, which favorable variations are preserved and unfavorable variations are eliminated. That's the theory of evolution in a nutshell," he said.

Berra discussed the journey that led Darwin to discover the theory of evolution.

Darwin started his career training at Edinburgh University to become a doctor, like his grandfather, father and brother.

Though Darwin went to school to become a doctor and follow in the footsteps of his family members, Berra said, he was horrified by the idea of surgery without anesthesia.

"Charles thought the medical lectures were boring and the horror of surgery without anesthesia was just too much for this sensitive young man to take," Berra said.

Eventually, he transferred out of medical school and into Cambridge University for Seminary where he met John Henslow, a botanist and professor.

According to Berra, Henslow influenced Darwin's career more than any other person.

Upon returning home after graduation, Darwin received a letter from Henslow offering him an opportunity to travel the world on a ship called the HMS Beagle.

Berra said Darwin had ambitions of writing a book and was inspired by Charles Lyle.

"Charles was filled with delight at the thought that he might write a book on the geology of the places he visited," he said.

Darwin is most famous for his work from the Galapagos Islands where he noticed differences in finches, tortoises and iguanas.

"Darwin had noticed the differences in the [finches] from island to island. Almost every biology text has some pictorial feature about Darwin's finches and how important they were to his ideas of natural selection," Berra added, "The truth is that while in the Galapagos, Darwin didn't realize the finches differed from island to island. It was only after he'd gotten back from the voyage when the artist began to study and illustrate the finches did it become clear that they too differed from island to island."

After returning to England, Darwin was back at Cambridge working with Henslow, who had shown Darwin's work to the scientific community.

Berra said it was almost a year after returning to England when Darwin first wrote his thoughts down about evolution.

"It was in July of 1837 that Darwin secretly entered his thoughts about the transmutation of species," Berra said. "At this time he had not yet thought about natural selection. In [one of the notebooks] he drew this irregularly branched tree that represented the common ancestry tree of all animals. This famous sketch was the first representation of an evolutionary tree."

According to Darwin's autobiography, it was a year after that when he first came to his theory of natural selection. After the publication of The Origin of Species, Darwin continued to write several different books and articles.

According to Berra, Darwin's grave is a few feet away from those of Isaac Newton and Charles Lyle.


http://www.independentcollegian.com/news/150-years-since-the-origin-of-species-1.2091102



We have NO sacred Cause to Fight for!

But Charles darwin had.

Please read!


To save Brahminism, Bhoodevatas are ready to sell the country itself

OUR CORRESPONDENT

Bangalore: Big news. Shocking news. Brahmins have finally decided to bid goodbye to their dead language, Sanskrit, and even their "national language", Hindi, and take to their hated anti-Hindu English. What is happening to this punya bhoomi?

The Hindu terrorist party, RSS, has decided to take to English in a big way because after good deal of trial and error it has found that English is better suited to hinduise (enslave) the non-Hindu, if not anti-Hindu majority masses comprising SC/ST/BCs —65%.

Brahmins (2%) any way have become rulers by taking to English. Their own Sanskrit called the language of the gods (meaning godmen) is even today not able to attract even 50,000 in a country of 130-crore population.

Anti-national English: Brahmins, the owners and drivers of the Sanskrit campaign Rath, have deserted their own language because it fetches not even a farthing. The so-called "national" dailies are published in the anti-national English, the language of the British "invaders" who brought the hated Christianity and corrupted the country.

The RSS has, therefore, decided to switch over to their hated English in all its Vidya Bharati Schools run by it.

http://www.sanghparivar.org/blog/vikas/improve-standard-of-english-all-sangh-supported-schools-in-india

http://www.sanghparivar.org/blog/vikas/improve-standard-of-english-all-sangh-supported-schools-in-india

http://www.asianage.com/presentation/leftnavigation/news/top-story/rss-s...

http://www.expressindia.com/news/fullstory.php? newsid=31167

Because it found that English alone is capable of attracting parents who send their children to Christian convents. Not only English schools will earn big money but can better brainwash the children in Hindu thoughts.

Vivekananda used English weapon: Christian schools are able to attract Dalit students because they teach in English and through English the missionaries are able to "convert" thousands of Dalits and Tribals into Christianity. Conversion has become a big headache to the Brahminists who are losing their slaves.

Did not Vivekananda "conquer" (mislead) the world through English? Is not the American CIA-controlled ISCKON spreading "Krishna culture thoughts" in English?

RSS is finally forced to admit that English has become the global language.

It is the Brahminical English journalists in Times of India, Hindu, Hindustan Times etc. who are propagating and strengthening Brahminism better than the Sanskrit-singing Kudmi papans.

If the logic adopted by the RSS is accepted soon the Brahmin temple priests too have to give up Sanskrit and take to English. If so how will their gods understand this "foreign language" as the gods know only Sanskrit? Then mantras have to be recited in English and the kudmi papans have to take to pant and shirt. What will happen to Hindu culture and its "glorious heritage"?

Punya Bhoomi in peril: What is happening to the Punya Bhoomi? Muslims invaded India and brought their cursed Arabic, Persian, Urdu languages. Then came the Christians with their anti-national English language. So much so in the 21st century Sanskrit, the language of gods, is dead. Even the "gods on earth" do not know it. They have all taken to English, make love in English, listen to Western music, Hindu culture is dead.

With the RSS decision to take to English, the fall of Hindu, Hindi and Hindustan has become total.

Dumping Sanskrit into Arabian sea: It is not yet known how far the idea of switching over to English is acceptable to the Khaki half-pantwalas of Nagpur. Now that a super-RSS is born in Abhinav Bharat, with its tail Ram Sena going on the rampage in Karnataka, will the Bhoodevatas dump their Sanskrit into the Arabian Sea?

Our fear is once the RSS Brahmins reject Sanskrit and even Hindi and take to English, will it not amount to the country's oldest and the most uncompromising "Hindu party" rejecting Hinduism itself?

History has said the Bhoodevatas, the "Jews of India", have been disguising and hiding themselves as Hindu. But once they take to English will it not destroy their "Hindu identity" itself?

Threat to Hindu civilisation: Hindu, Hindi, Hindustan brought them such great dividends, made them rulers of the land (nay dictators) after partition of India. And then killing their own Mahatma.

Brahmin scholars have been boasting that "Hindu civilisation" developed around their Sanskrit scriptures. They also said that Sanskrit was the language of the Indus Valley civilisation of which they were the founders. If this is agreed will not accepting English destroy all that they claimed — including the world's most ancient Hindu civilisation?

http://www.dalitvoice.org/Templates/nov_a2009/reports.htm



Darwin's Sacred Cause

Authors Adrian Desmond and James Moore are very clear in their view that social context is crucial for understanding anyone, whether they lived in generations past, or whether they are alive today. They have applied this thinking to Charles Darwin. They are aware that not all share their approach or enthusiasm:

"Many scientists and philosophers think that explaining genius and its insights as we do saps the power of science and, given the challenge of creationism, is an act of treachery. The reluctance to dig beneath the surface of Darwin's books into the social and cultural resources of his times is as dogged as ever."

These two have been working on a sequel to their 1991 biography of Darwin and their publisher is claiming they have come up with a "revolutionary thesis". The book is said to be "astonishing". They suggest that Darwin's abhorrence of slavery was a major driver for his evolutionary theorising.

"One such resource in Darwin's world was anti-slavery, the greatest moral movement of his age. Our thesis is that the anti-slavery values instilled in him from youth became the moral premise of his work on evolution."
and
"We are not trying to explain away all of Darwin's work as being due to his passion for emancipation, but our argument is that his passion for racial unity is what drove him to touch this untouchable and treacherous subject."

Book cover
The new book (source here)

Although the book is not yet published, Desmond and Moore did provide an extended abstract of their thinking in the Introduction of a new edition of The Descent of Man, published in 2004. This attracted some critical analysis in the pages of The British Journal for the History of Science. It is worth highlighting some of the points in that review, because it sets an agenda for evaluating the significance of the new book, when it appears. The reviewer, Robert J. Richards, finds the thesis implausible on several counts. First, he finds that their case is built on inference rather than direct evidence:

"This account of Darwin's motivation for his theory of human evolution does suffer the inconvenience of being unsupported by any evidence. Darwin certainly was a foe of slavery. His abolitionist sentiments were nurtured in the enlightened Whig household of his father and voluble sisters, and his hatred of slavery became incandescent as the result of poignant experiences in South America. But there is no indication in the Descent - or elsewhere - that he formulated his conception of human evolution in order to undermine the peculiar institution."

Secondly, Darwin did exhibit a tendency to racialism. Rather than take opportunities to stress the equality of the various human races, he drew attention to their differences and linked this with the demise of some.

"Despite Moore and Desmond's suggestions to the contrary, in his book Darwin described the races as forming an obvious hierarchy of intelligence and moral capacity, from savage to civilized, with the 'intellectual and social faculties' of the lower races comparable to those that must have characterized ancient man (p. 209). Accordingly, he ventured that 'the grade of their civilisation seems to be a most important element in the success of competing nations' (p. 212), which explained for him the extermination of the Tasmanians and the severe decline in population of the Australians, Hawaiians and Maoris. Those groups succumbed in struggle with more advanced peoples (pp. 211-22). In this respect Darwin was no different from Haeckel, whose conception of 'human genealogy' the Englishman emphatically endorsed in the introduction to his book (p. 19)."

The trail divides sharply when these authors consider how sexual selection was addressed by Darwin. First, Desmond and Moore's analysis:

"The pair claim in a new book that Darwin partly chose to highlight the common descent of man from apes to show that all races were equal, as a rebuttal to those who insisted black people were a different, and inferior, species from those with white skin. They say Darwin attempted to show that his theory of sexual selection, where traits seen as desirable but which give no competitive advantage to a species are passed down through generations, was responsible for differences in appearance between races of both animals and humans."

By contrast, this is from Robert Richards:

"In the late 1860s Darwin and Wallace had a protracted disagreement about how sexual selection operated in birds and other organisms - hence Darwin's cascading discussions in the second volume of his book (almost four hundred pages) of sexual selection in beetles, butterflies, birds and bucks. But an even more significant dispute with Wallace arose because of his friend's conversion to spiritualism. Wallace had come to argue that the distinctive features of human beings - naked skin, aesthetic sense, moral character and large intellect - could not be explained by natural selection because such traits conferred little or no survival advantage. Only higher spiritual powers could have produced them. Darwin accepted Wallace's analysis that these traits could not be explained by natural selection, but he did not fall prey to Wallace's new faith. Rather, he proposed other powerful but natural forces to account for the distinctive traits characterizing human societies, namely the forces of sexual selection and group selection - elegant solutions to a vexing conceptual problem."

These issues were highlighted two years ago and the advance blurb of the book does little to raise confidence that they have been addressed. We do not doubt that Darwin was shocked by slavery. We do not doubt that he had relatives and friends who were active abolitionists. The question being raised is: Was Darwin motivated by these convictions in developing his ideas in The Descent of Man? Alternatively, was he motivated by a grand vision of all life as the unfolding of a naturalistic evolutionary process? These issues will no doubt be explored further during this Bicentennial year. But to conclude this blog, here is something on which we agree with Desmond and Morris (and which goes against much of the rhetoric about the "pure" science associated with Darwinism:

Question: What lessons does this book contain for the relationship between religion and science?
"That 'the relationship between religion and science' never existed; that religion in science was the norm in Darwin's day, and he never escaped its aura; that biological theorizing about human nature inevitably poses moral questions, and in so far as these questions have religious answers, to that extent 'religion and science' are inseparable."

Darwin's Sacred Cause: How a Hatred of Slavery Shaped Darwin's Views on Human Evolution
by Adrian Desmond and James Moore
Allen Lane, Publication date: 29 Jan 2009

An astonishing new portrait of a scientific icon. In this remarkable book, Adrian Desmond and James Moore restore the missing moral core of Darwin's evolutionary universe, providing a completely new account of how he came to his shattering theories about human origins. [snip]

Review of new edition of The Descent of Man
Robert J. Richards
The British Journal for the History of Science (December 2006), 39:4:615-617 | doi:10.1017/S0007087406409055

1st para: James Moore and Adrian Desmond have brought out a new paperback edition of Darwin's Descent of Man, and Selection in Relation to Sex. They chose the final printing (1879) of the second edition (1874) as the text, which for scholars will serve as a handy companion to the first edition (1871), readily available from Princeton University Press. For teaching purposes, the Penguin version may even be preferred to the first edition because of the inclusion of a chronology of Darwin's life, an appendix containing thumbnail sketches of individuals named in the text and, most especially, Moore and Desmond's provocative fifty-page introduction - an introduction admirable in its social detail and implausible in its deflationary thesis.

See also:

Gray, R. Charles Darwin's research to prove evolution was motivated by his desire to end slavery, Telegraph Online, 24 Jan 2009.

A Conversation with Adrian Desmond and James Moore.

Flannery, M. Darwin's "Sacred" Cause: How Opposing Slavery Could Still Enslave, Uncommon Descent (16 February 2009)

http://www.arn.org/blogs/index.php/literature/2009/01/27/darwin_s_sacred_cause



19th of March 2009, 6:00 PM


The Linnean Society of London was delighted to welcome Professor James Moore on 19th March 2009 to speak on "Darwin's Sacred Cause".

Professor Moore began his talk, by reading a contemporary narrative, reminiscent of Darwin's experience of the slave trade in operation whilst on his Beagle voyage in 1832. Professor Moore reflected that due to his family's involvement in the anti-slavery movement, Darwin had been habituated to anti-slavery propaganda since youth; but only at this point did he face the brutal reality.

Darwin's family were great supporters of the anti-slavery cause; Darwin's Aunt Sarah, gave more money than any other female donor to movement and Darwin's sisters were passionate abolitionists. Erasmus Darwin had also been very much involved, corresponding with Josiah Wedgwood, about the subject. It was, Professor Moore asserted the Unitarians including the Darwins and Wedgewoods who had engaged in the anti-slavery campaign well before the more famous "Anglican Saints", including William Wilberforce; and Darwin's family continued to support the Saints with the Wedgwoods pledging large donations to the campaign organised by Thomas Clarkson, founding the Hanley and Shelton Anti-Slavery Association and, through this, distributing large numbers of copies of anti-slavery literature.

Darwin's first encounter with a former slave, was as an undergraduate at the University of Edinburgh.  Here, he was taught taxidermy by John Edmonston, a freed Guyanese slave who lived in the same street as Darwin. His interaction with John confirmed Darwin's belief that white people and black people possessed the same essential humanity. His move to Cambridge – the "spiritual home" of the anti-slavery movement served to underline his anti-slavery thinking.

Following his undergraduate studies at Cambridge, Darwin was asked if he would be interested in joining Captain Robert FitzRoy on a second surveying voyage in the Beagle. Fitzroy had taken command of the vessel on it's first voyage, following the suicide of the Captain and had returned in 1830, with four captives from Tierra del Fuego. His aim was that they should be Christianised and returned to their homeland as missionaries.  Thus, when Darwin joined Fitzroy on the second voyage, they were accompanied by the three surviving Fuegians. 

Professor Moore reflected that Darwin's experiences on The Beagle served to promote two lines of thought; they increased his abhorrence of the slave trade and spurred his thinking about evolution. 

Darwin's first encounters with the slave trade (beyond the printed page)  occurred during the Beagle voyage. Whilst in Rio, he was shocked to witness slaves landed on the beach and to see the thumbscrews used for the punishment of female slaves. His views caused considerable friction between himself and Fitzroy. Professor Moore also commented that Darwin's experiences informed his thinking regarding evolution as he lived alongside the Fuegian captives, observing their transformation into anglicised Christians and then their reversion to their former "wild state" by the time he returned to visit them in Tierra del Fuego in 1834; this prompted the analogy of savage as wild and civilised as domesticated, which spans his work. Darwin also observed the similarities and differences between the Fuegian and the Patagonian races, refusing to accept the latest evolutionary idea that they were unrelated species of the human genus. Both Darwin and Fitzroy, as part of their Christian heritage, believed that all the races were members of the same human family. Others however, were postulating 15 or more species of ape, which had evolved separately into 15 geographically-distinct human species. Although Darwin regarded plural racial origins as abhorrent and immoral, he began to consider some natural explanation for the obvious differences between races. 

Hence, soon after the Beagle voyage ended in 1836, Darwin committed himself to an evolutionary origin of species. His experiences led him to a unique image of evolution, not one of parallel linear descent as taught by Lamarckians such as his teacher Dr Robert Grant at the University of Edinburgh, but one of branching common descent. This tree-image united all the races, plant, animal and human alike; and Darwin referred to the arrogance of slave masters for considering black people as an`other kind' different to themselves. This pluralist viewpoint was defended with great authority in Darwin's day by the Harvard zoologist Louis Agassiz who held that eight human `types' or species had appeared in different geographical zones as part of a God-ordained creative sequence; all humans were God's children but the races were intended to be separate and unequal. Others did publish work to counteract this pluralism, especially Dr James Cowles Prichard, whom Darwin read carefully and cited generously. Prichard may have believed in Adam and Eve and Noah's Flood, but he still argued that the human races had developed naturally, as the products of climate, culture and selective mating.

Professor Moore concluded his talk by discussing Darwin's production of his seminal work On the Origin of the Species which he began to write in 1856 and was intended to cover human racial origins. His plans to write a book on species were widely known and, a year later, Wallace corresponded with him to ask if he would discuss `man' in the book; Darwin's response was No - the subject was surrounded by too much prejudice. The Origin of Species did however bring together his research on the natural production of pigeon races, which he knew was analogous to the making of the human races. And Darwin'wore his morals on his coatsleeve: in the Origin he called slave-making in ants as an "odious instinct"; and in the Descent of Man in 1871 he referred to the "great sin of slavery". Darwin remained an ardent abolitionist, corresponding with Richard Hill, the first man of colour appointed as a magistrate in Jamaica after the abolition of slavery. Mr Hill specialised in adjudicating between freed slaves and their former owners, and of this Darwin remarked "I was quite delighted...to hear of all your varied accomplishments and knowledge, and of your higher attributes in the sacred caused of humanity".


http://www.linnean.org/fileadmin/events2/events.php?detail=161


Darwin's Sacred Cause:

How a Hatred of Slavery Shaped Darwin's Views on Human Evolution

by Adrian Desmond and James Moore

$30.00 List Price

For more info visit:
Amazon • IndieBound

Banquet at Delmonico's:

Great Minds, the Gilded Age, and the Triumph of Evolution in America

by Barry Werth

$27.00 List Price

For more info visit:
Amazon • IndieBound

In 2001, the Education Committee of the Louisiana House of Representatives passed a resolution rejecting "the core concepts of Darwinist ideology that certain races and classes of humans are inherently superior to others." The resolution's sponsor, an African-American Democratic legislator, asserted that by teaching "that some humans have evolved further than others," the nineteenth-century English naturalist Charles Darwin "provided the main rationale for modern racism." Upping the ante, Expelled, last year's documentary-style motion picture by entertainer Ben Stein, who is Jewish, blamed the Holocaust on Nazi racism rooted in Darwinian science.

These claims have long enjoyed currency in America's influential evangelical sub-culture, where opposition to Darwinism runs deep. From the 1940s until his death in 2006, Henry M. Morris, who founded the Institute for Creation Research with megachurch minister and best-selling author Tim LaHaye, wrote and lectured widely about the supposed social consequences of believing in Darwin's theory of organic evolution rather than the biblical account of special creation. In one representative series, the Modern Creation Trilogy, Morris complains that "practically all the harmful practices and deadly philosophies that plague mankind have their roots and pseudo-rationale in evolutionism."

This dire view of Darwin and his works must prompt some creationists to wonder about the spate of laudatory conferences, exhibits, and programs scheduled to celebrate the two-hundredth anniversary of his birth on February 12, 1809. In Britain, home to the greatest concentration of such festivities, Darwin's image appears on the ten-pound note, and his home is a national landmark. To his more polemically minded religious critics, all the hoopla must seem like throwing a birthday party for Hitler. Nevertheless, most scientists and virtually all biologists view life through the lens of Darwin's theory of organic evolution by natural selection. They typically hail him as a dogged researcher and brilliant theorist who exemplified the best practices of a modern scientist. These supporters often see his theory, when applied to humans, as a means to unify the races under a common ancestry and find a shared ethic for all peoples.

Given both Darwin's scientific stature and the resonance of the religious disputes surrounding the theory of evolution, it's no surprise that accounts of his life and work fuel a robust cottage industry. Two new books—initial entries in a stable of forthcoming bicentennial-minded studies—creatively reexamine the nineteenth-century sources and uses of Darwinism in its most contentious arena: the controversies over slavery and racism.

With Darwin's Sacred Cause, Adrian Desmond and James Moore execute the notable feat of authoring a second revisionist biography of the same man. Their ab-sorbing Darwin: The Life of a Tormented Evolutionist (1991) presented the naturalist's story as a lifelong struggle with religion that ended in a gentle but firm agnosticism. Now, Desmond and Moore are back with a book that should surprise those who see Darwin as the father of modern racism. Without rebaptizing him into the church, Darwin's Sacred Cause puts him in the same congregation with those nineteenth-century British and American evangelicals who led the crusade against slavery.

Like such recent best-selling histories as Erik Larson's delightful The Devil in the White City, the authors shift between two concurrent story lines, in this case Darwin's biography and the saga of the Anglo-American abolition movement, with emphasis on their points of intersection. Both are grand tales, and they complement each other in the telling—even if the connections seem strained at times. For example, without conclusive evidence, the authors suggest that Darwin studied the ability of seeds to reproduce after immersion in seawater as a means of refuting naturalist Louis Agassiz—and solely because Darwin wished to undermine Agassiz's proslavery theory of separate creations for species and races. However, oceanic dispersal of seeds is needed for evolution to account for the geographic distribution of plants, and that alone could more simply justify Darwin's study of it.

Desmond and Moore highlight two underappreciated themes. First, from the outset of his work on evolution, Darwin was mainly interested in the origin and development of the human species. This was obscured by his tactical decision not to dwell on that sensitive subject in On the Origin of Speciesbut as the authors show, his earliest scientific writings reveal a preoccupation with human evolution. Indeed, they write, "it was in Tierra del Fuego, perplexed and troubled by an alien race [of primitive humans], that Darwin decided to spend his life studying natural science." His subsequent notebooks are filled with comparisons of these and other peoples with apes and higher primates. This book dispels the legend, long attached to retrospective accounts of Darwin's research, that the great scientist's interest in evolution was spurred by Galapagos finches. It was people all along.

Second, despite his often-blunt comments about Fuegians and other aboriginal peoples—whom he depicted as doomed in their struggle for survival against Europeans—Darwin shared his family's abhorrence of slavery. Desmond and Moore connect these two themes in his life to argue that the moral passion firing his work derived from his desire to undermine the support for slavery provided by antebellum theories of separate creations for the races. These pluralist theories, which also aroused the ire of biblical literalists, derived mostly from the self-serving view of Southern slaveholders and their apologists that human races, like biological species, never change. Yet Desmond and Moore concede that Darwin maintained a hierarchical view of race and made ribald references in his writing to "Slave-making" ants. Ample evidence exists of other reasons for Darwin's interest in evolution. Desmond and Moore mainly show that Darwin appreciated the value of his theory to counter pluralist theories of race. By doing so, they shed welcome light on lesser-known features of Darwin's work, while also providing an exceptionally crisp account of mid-nineteenth-century debates over the origins of racial differences.

Where Desmond and Moore artfully balance two narratives to advance a strong thesis, in Banquet at Delmonico's Barry Werth jumps around among a dozen or so concurrent story lines to provide a patchwork chronicle of the American intelligentsia from 1871 to 1882. With each chapter covering the events of one year, the result is a lively but disjointed popular history of a deeply conservative age. The book opens just as laissez-faire capitalism has concentrated unprecedented wealth in the hands of Northern industrialists, Civil War–era dreams of black opportunity have faded into post-Reconstruction acceptance of Southern white supremacy, the US Army has almost completed the process of penning Native Americans into reservations, and a philosophy of social Darwinism has emerged to justify all of these developments as natural, inevitable, and even benevolent. If, as Desmond and Moore suggest, Darwin viewed his theory as an argument for treating humans equally—and such a claim remains dubious—then Werth shows that it did not necessarily have that immediate effect on American social thought.

Darwin appropriately gives way in Werth's account to British social philosopher Herbert Spencer as the key mediating figure in the triumph of evolutionism in the New World. Although Darwin's work enabled evolutionary theory to prevail in the scientific comunity, Spencer's popular philosophy gave a social meaning to evolutionism that inspired such influential Americans as industrialist Andrew Carnegie, sociologist William Graham Sumner, historian John Fiske, politician Carl Schurz, paleontologist O. C. Marsh, attorney William Evarts, and pastor Henry Ward Beecher. Werth's book follows each of these characters through the twelve-year period that culminated in their celebratory 1882 banquet for Spencer, hosted by his American publisher, Edward Livingston Youmans, at New York's elegant Delmonico's restaurant.

Darwin never banqueted in the United States, but he appears in Werth's book interacting with his American supporters and critics, some of whom are also featured in Darwin's Sacred Cause facing off in antebellum debates over slavery and racial origins. Both books remind us of the complex social uses of Darwinism, some good and some bad. Banquet at Delmonico's concludes with evolutionism ascendant among American intellectuals even as lawmakers had begun to usher in an era of racial segregation and eugenic sterilization. The link between Darwinism, slavery, and modern racism remains highly disputed, however, and these books will not resolve the argument. If Werth had chosen to investigate American thought more broadly, he would also have found unrelenting opposition to Darwinism among conservative Christians. Many of these American anti-evolutionists were at least as racist as some of their pro-evolution counterparts.

Neither science nor religion offers any guarantee against bigotry or racism. Their social impact largely follows from what we make of them. That is at least one lesson to be gleaned from the ongoing battles between creationists and evolutionists over the moral implications of Darwinism. Another is that, even though the baldly racialist tenor of the debate has largely subsided, the struggles launched in the nineteenth century over evolutionism remain very much with us— even in this year of Darwin's bicentennial.

Edward J. Larson is the author of the Pulitzer Prize–winning Summer for the Gods (Basic Books, 1997).

http://www.bookforum.com/inprint/015_05/3278


WEIT and Darwin's Sacred Cause reviewed in Washington Post

Yesterday's Washington Post reviewed my book together with Adrian Desmond and James Moore's new book, Darwin's Sacred Cause: How a Hatred of Slavery Shaped Darwin's Views on Human Evolution. An o.k. review for me, though the "too textbooky" comment stung a bit. More important, it described Desmond and Moore's book in detail, and in a way that will make us all want to read it. Darwin's Sacred Cause apparently rests on the authors' thesis that Darwin's writings on evolution, including The Origin, were part of a detailed plan to demolish slavery by proving the common ancestry of all races. This idea, which is certainly novel, is said to be supported by detailed scholarly research (those who have read the authors' earlier biography of Darwin—and every Darwin fan should—know how thorough these authors are and how well they write). Clearly this is a must-read book for all of us.

A footnote:  although Desmond and Moore's Darwin biography is great, I give the edge to Janet Browne's two-volume work (link is to second volume) as the best among Darwin biographies. It is magisterial and engagingly written.




Darwin's Sacred Cause

As any Darwin aficionado will tell you, as this celebratory week draws to a close, there is one biography of Charles Darwin that stands out from the crowd.

James Moore, Olivia Judson, and Adrian Desmond at Imperial College

James Moore, Olivia Judson, and Adrian Desmond at Imperial College (photo Tim Jones)

Olivia Judson and Adrian Desmond at Imperial College (photo Tim Jones)

Olivia Judson and Adrian Desmond at Imperial College (photo Tim Jones)

James Moore & Olivia Judson at Imperial College (photo Tim Jones)

James Moore & Olivia Judson at Imperial College (photo Tim Jones)

Not only is Adrian Desmond's and James Moore's 1991 'Darwin' comprehensive at 677 pages before the notes, it's brick-like iconicity somehow speaks of closure, the last word, to any further debate about Darwin.

On a personal note, not withstanding Janet Browne's Voyaging and Power of Place, which are both excellent reads, and show that Darwin was not in fact the last word, I have a particular affection for the Desmond and Moore biography.   It's simply one of the few books of  length that I've ever  found the right combination of time and inclination to read right through non-stop; it took about a week one Christmas holiday.  And as with all good biographies of departed figures, that level of immersion leaves one genuinely saddened when the subject dies.

Adrian Desmond talks about Darwin's Sacred Cause (photo Tim Jones)

Adrian Desmond talks about Darwin's Sacred Cause (photo Tim Jones)

So it was with some interest last Monday, that I walked the whole 100 feet  or so from my department at Imperial College to the Great Hall, to join a public conversation with Olivia Judson interviewing Adrian Desmond and James Moore.  The theme -  the authors'  NEW book, 'Darwin's Sacred Cause'.

James Moore

James Moore

This post isn't a book review.  As much as I'd like to drop everything else and read it – I haven't found the time yet!   Thankfully, it looks nothing in length like (as Desmond reminded us at this session) 'the brick'.

Olivia Judson

Olivia Judson

Rather – before it becomes completely old news, I'll point you to this online lecture podcast from Imperial College that helpfully captures the whole session.

That said, as a brief preview, the focus of the conversation is around Darwin and race, and the argument that man (as opposed to finches and other animals) was the core motivation behind developments in the theory of natural selection and the writing of the Origin of Species.  The Origin itself, we are told, was originally conceived to include extensive discussion on man and race.  The authors further link Darwin's feelings about race back to a family upbringing and tradition steeped in benevolence and an active opposition to slavery.

Enough said for now – maybe more when I've read the book!


Rough Guide to Evolution: Did the death of his daughter cause Darwin to give up Christianity?



Did the death of his daughter cause Darwin to give up Christianity?
Well, I guess I cannot continue keeping readers in suspense as to why I have concluded that the death of Annie Darwin had nothing to do with Darwin's abandonment of Christianity, so I am going to re-draft my paper for release on this blog (complete with hypertext links). However, as the paper is quite long and it may take me a day or two to convert it, I will release it as a series of blog posts, rather than all in one go. Here is the first installment. I welcome comments, additions, or corrections. Please let me know, as we go along, whether I have convinced you of my argument.
Did the death of his daughter cause Darwin to give up Christianity?
"A long habit of not thinking a thing WRONG, gives it a superficial appearance of being RIGHT" Thomas Paine, Common Sense

"To establish one hypothesis upon another, is building entirely in the air; and the utmost we ever attain, by these conjectures and fictions, is to ascertain the bare possibility of our opinion; but never can we, upon such terms, establish its reality."
David Hume, Dialogues concerning Natural Religion
Introduction
If you ask the average man or woman what they know about Charles Darwin, one of the dozen or so "facts" that he or she is likely to come up with is that Darwin lost his religious faith as a result of the death of his daughter Annie. Some might also claim that Annie died from tuberculosis and her death influenced Darwin's later writing on evolution. These claims have wide currency on the Internet, in popular and scholarly publications and even on screen (see Table and list in previous postings).
However, it might surprise you to learn that there is no direct documentary evidence to support these claims in anything written by Darwin or any of his associates—instead, here we argue, they should be classified, along with Darwin's finches and Darwin's delay, as modern "Darwin myths", which have arisen only in recent times and were wholly unknown to Darwin, his contemporaries and several subsequent generations of scholars. In fact, scrutiny of Darwin's own manuscripts, publications and correspondence and other writings of his period suggests that, not only are these claims unsupported by the evidence, they are likely to be wrong.

Thanks to the Darwin Correspondence Project (http://www.darwinproject.ac.uk) and Darwin Online (http://darwin-online.org.uk/), almost all sources of information on Annie's life and Darwin's religious beliefs from Darwin and his associates are now available on-line. We have provided a list of links to this original material, so the interested reader can easily verify our assertions and conclusions.

What do we know about the life and death of Annie Darwin?
Let us start by considering what we know of Annie Darwin. The bare facts are that Anne Elizabeth Darwin was born on 2 March 1841 in London and died on 23 April 1851 in Malvern, after an illness that lasted at least several weeks and perhaps as long as nine months. She was Darwin's second child of ten and one of three to die in childhood. Darwin mentions Annie as a baby briefly in his 1877 paper A Biographical Sketch of an Infant, a publication generally devoted to observations on her elder brother William:
"he [William] held pencils, pens, and other objects far less neatly and efficiently than did his sister [Annie] who was then only 14 months old, and who showed great inherent aptitude in handling anything"
Before her final illness, Annie features in seventeen of Darwin's letters, usually in statements of affection (e.g. "not so bad a girl", "I long to kiss Annie's botty-wotty"), praise ("Annie is something... a second Mozart") or humour ("Miss Annie is not quite ready to be married yet"). She is also mentioned a dozen or so times in the Notebook of observations on the Darwin children maintained by Charles and Emma, with Emma noting at age three and a half:
"Obstinacy is her chief fault at present."
Sometime before her tenth birthday, Annie fell ill. A retrospective note in Emma's diary for 27 June 1850 records:
'Annie first failed about this time'

and Darwin himself wrote

"Her health failed in a slight degree for about nine months before her last illness".
According to her sister Henrietta, a family trip to Ramsgate in October 1850 was made on account of Annie's poor health. On 24th March 1851, Darwin took Annie to Malvern in the hope that the water cure espoused by Dr James Gully would lead to a cure. Darwin left Annie in the care of her nurse Brodie, who was joined by the family governess, Miss Thorley a few days later. Darwin was summoned back to Malvern on April 15th and arrived on the 17th.

The series of letters that followed between Charles and Emma Darwin provide a poignant record of the hopes and fears of the parents of dying child. A single entry, chilling in its terseness, in Emma's diary for April 23rd records the time of Annie's death: "12 o'clock".

That Annie's death caused distress to her parents and family is beyond dispute. A week after her death, Darwin penned a tender memoir of Annie, which was published in part by his son, Francis in 1887 in The life and letters of Charles Darwin and in full by Colp in 1987 (Colp R Jr. 1987. Charles Darwin's "insufferable grief". Free Associations 9: 7-44.). Darwin closes the memoir with the cry from the heart:

"We have lost the joy of the Household, and the solace of our old age:— she must have known how we loved her; oh that she could now know how deeply, how tenderly we do still & shall ever love her dear joyous face. Blessings on her."


Darwin also mentions Annie's death in his Autobiography (15):
"We have suffered only one very severe grief in the death of Annie at Malvern on April 24th, 1851, when she was just over ten years old. She was a most sweet and affectionate child, and I feel sure would have grown into a delightful woman. But I need say nothing here of her character, as I wrote a short sketch of it shortly after her death. Tears still sometimes come into my eyes, when I think of her sweet ways."
But the above links provide pretty much all we have from Charles and Emma Darwin on their daughter Annie. Let us be clear—nowhere in the millions of words that flowed from his pen does Darwin ever say that Annie's death had anything to do with his own loss of faith. Indeed, as we shall see, the balance of evidence is that Annie's death had nothing to do with Darwin's loss of religious belief.
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First published online December 19, 2008; doi:10.3732/ajb.0800126
American Journal of Botany 96: 366-381 (2009)
© 2009 Botanical Society of America, Inc.
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Special Invited Papers

Darwin's second 'abominable mystery': Why are there so many angiosperm species?1

William L. Crepet2 and Karl J. Niklas

Department of Plant Biology, Cornell University, Ithaca, New York 14853 USA

ABSTRACT

The rapid diversification and ecological dominance of the flowering plants beg the question "Why are there so many angiosperm species and why are they so successful?" A number of equally plausible hypotheses have been advanced in response to this question, among which the most widely accepted highlights the mutually beneficial animal–plant relationships that are nowhere better developed nor more widespread than among angiosperm species and their biotic vectors for pollination and dispersal. Nevertheless, consensus acknowledges that there are many other attributes unique to or characteristic of the flowering plants. In addition, the remarkable coevolution of the angiosperms and pollination/dispersal animal agents could be an effect of the intrinsic adaptability of the flowering plants rather than a primary cause of their success, suggesting that the search for underlying causes should focus on an exploration of the genetic and epigenetic mechanisms that might facilitate adaptive evolution and speciation. Here, we explore angiosperm diversity promoting attributes in their general form and draw particular attention to those that, either individually or collectively, have been shown empirically to favor high speciation rates, low extinction rates, or broad ecological tolerances. Among these are the annual growth form, homeotic gene effects, asexual/sexual reproduction, a propensity for hybrid polyploidy, and apparent "resistance" to extinction. Our survey of the literature suggests that no single vegetative, reproductive, or ecological feature taken in isolation can account for the evolutionary success of the angiosperms. Rather, we believe that the answer to Darwin's second "abominable mystery" lies in a confluence of features that collectively make the angiosperms unique among the land plants.

Key Words: agamospermy • angiosperm diversification • annual growth form • floral trait evolution • homeotic genes • polyploidy • species morphospace

Received for publication 3 April 2008. Accepted for publication 13 October 2008.

FOOTNOTES

1 The authors thank Drs. B. H. Tiffney (University of California, Santa Barbara) and K. Pigg (Arizona State University) for valuable suggestions to improve an early draft of this paper, which we dedicate to Verne Grant whose pioneering work in the field of angiosperm speciation and biology is as relevant today as it was in the last century.

2 Author for correspondence (e-mail: wlc1@cornell.edu)


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George James Grinnell1

(1) History Department, McMaster University, L8S 4L9 Hamilton, Ontario, Canada
Conclusion  ldquoThe difficulty of discussion between people brought up in different frameworks is to be admitted,rdquo Karl Popper writes. ldquoBut nothing is more fruitful than such a discussion; than the culture clash which has stimulated some of the greatest intellectual revolutions.rdquo71 Certainly Kirby and Darwin were brought up in different cultures — Kirby with his Anglican-Tory orientation, Darwin with his Whig-liberal background — and certainly the clash generated some interesting theories; but it also resulted in the revival of Lamarck's discredited habit theory, which took another century of careful experimentation to weed out.
http://www.springerlink.com/content/p708j4n883765644/

Natural Selection: Darwin's Dangerous Idea


SUMMARY:

Charles Darwin's theory of evolution by natural selection is both a useful and a "dangerous" idea. This is because Darwin's theory provides a naturalistic foundation for biology, but also undermines the idea of purpose in nature and the concept of human free will. Darwin proposed two ideas in the Origin of Species: "descent with modification" (what we now call "evolution") and natural selection (the process by which evolution proceeds). In Darwin's theory, natural selection is both the "engine" of evolution and the explanation for the origin of adaptations.

Darwin's theory is based on three pre-conditions:
Variation (i.e. differences between individuals in populations),

Inheritance (from parents to offspring), and

Fecundity (i.e. the tendency for all organisms to produce more offspring than are necessary to replace themselves).

These three pre-conditions entail the following outcome:
Natural Selection: Some individuals survive and reproduce more often than others, and as a consequence their heritable characteristics become more common over time.

Central to Darwin's theory is that it is not necessary to assume that evolution by natural selection has any purpose. Like all natural processes, it proceeds via natural laws that are combinations of chance and necessity alone.

EVOLUTIONARY PSYCHOLOGY 1.1.3


Daniel Dennett, a prominent philosopher of science, said this about Darwin's theory of evolution by natural selection:
"If I were to give an award for the single best idea anyone ever had, I'd give it to Darwin, ahead of Newton and Einstein and everyone else. In a single stroke, the idea of evolution by natural selection unifies the realm of life, meaning, and purpose with the realm of space and time, cause and effect, mechanism and physical law. But it is not just a wonderful scientific idea. It is a dangerous idea."

Darwin's work has had an enormous impact on society, perhaps more than that of any other scientist. His books have changed the world, and will continue to change it for the foreseeable future. His ideas have revolutionized science, and not just biology. By the end of the 20th century, it had become clear to intellectuals in both the sciences and the humanities that the idea of evolution by natural selection could be applied almost without limit to understanding not only life on Earth, but also much of the human condition itself.

And therein lies the "danger" to which Dennett alludes, because Darwin's theory of evolution undermines not only the creation stories central to the world's dominant religious, it also undermines the very idea of purpose in nature and the concept of human free will. Even atheists have trouble with Darwin's ideas, especially his idea of natural selection. In this lecture, I intend to show how Darwin's ideas apply to an understanding of human behavior, and why such ideas might be "dangerous," and at the same time indispensable to understanding where we have come from and why we do what we do.

Darwin's most famous and most important book was entitled: On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. At first glance, this seems a typically long-winded Victorian book title, but on closer examination it neatly separates Darwin's "one long argument" into its two separate but interrelated parts:
An argument for the "transmutation of species" – what Darwin called "descent with modification" and we now refer to as "evolution,"

and

An argument for how evolution happens – natural selection – and how it produces the seemingly purposeful adaptations we see in living organisms.

At the time of its publication the most immediately controversial idea that Darwin presented in the Origin of Species was the idea that species could change over time. In particular, Darwin implied (but did not explicitly state in the Origin) that humans had evolved from "lower forms of life" (ape-like primates, to be exact).

Although in the Origin Darwin merely implied that "Light will be thrown on the origin of man and his history," both his critics and his supporters immediately began arguing about the evolutionary origins of humans, an argument that Darwin finally addressed twelve years later in The Descent of Man and Selection in Relation to Sex. And not just humans: According to Darwin's theory, the diversity of all organisms, living and extinct, could be explained as the result of descent with modification, which Darwin suggested could also be used to revise the taxonomy of life on Earth.

Almost as controversial at the time of the publication of the Origin, and growing ever more so since then, was Darwin's proposed mechanism for such evolution – natural selection – according to which,
there was no reference to supernatural forces whatsoever, especially in the first edition,

and

blind and purposeless natural forces – variation, heredity, fecundity, and unequal survival and reproduction – were all that were necessary to explain the extraordinary diversity and adaptive perfection of living systems.


DARWIN AND THE ORIGIN OF SPECIES


What makes his accomplishment all the more surprising is that Darwin was not much of a scholar. Indeed, as a young man, Darwin showed almost no interest in academics. Gertrude Himmelfarb, a historian of science who wrote a book about Darwin and the Origin of Species asked:

"Why was it given to Darwin, less ambitious, less imaginative, and less learned than many of his colleagues, to discover the theory sought after by others so assiduously?"

According to his autobiography, Darwin studied latin, greek, and mathematics in primary school, but without distinguishing himself as a good student. His greatest interest as a boy was in collecting things – stamps, rocks, birds' eggs, etc. – and in taking long walks in the country.

His primary interests in college were hunting and collecting beetles. His father, a prosperous physician, wanted him to become a doctor (his older brother, Erasmus, was already a doctor), and so sent him to Edinburg University to study medicine with his brother. However, Charles couldn't stand to witness surgery being performed on children without anesthetic, and so he quit medical school. His father then recommended that he become a country parson, so Darwin entered Cambridge University, where he earned a degree in theology. He was, at best, an indifferent student, earning what amounted to a "gentleman's C".

In later years he said that he had forgotten virtually everything he had learned while at Cambridge, with the exception of two books by William Paley:
A View of the Evidences of Christianity, in which Paley tried to dismantle David Hume's attack on miracles

and

Natural Theology, in which Paley presented the argument for design in nature.


So, how could Darwin have written the most important book in biology, if not all of science? There are several aspects of Darwin's character that could explain this apparent anomaly:
Darwin was an extraordinarily avid collector, especially of natural objects. For example, he once tried to capture three beetles (for his collection) by popping one in his mouth and one in each hand. Unfortunately, the one in his mouth exuded an acrid fluid, causing him to drop and lose all three beetles.

Darwin was very deeply interested in geology, as a result of a course he had taken in Cambridge. It was not uncommon for students in training as parsons to take courses in geology and natural history, as many of them were also amateur naturalists. Darwin showed an unusual interest in geology, which impressed his teacher, Professor Sedgwick, to take him on many field trips throughout England to study the various landforms and rock formations.

Darwin was also very interested in botany and "natural history" (what biology was called in those days). His botany teacher, Professor Henslow, thought so much of his talents that he recommended that Darwin be appointed as ship's naturalist for the voyage of HMS Beagle (a post Henslow himself had been offered, but turned down due to family responsibilities).


Darwin jumped at the chance to serve as ship's naturalist aboard the Beagle. However, the Beagle's captain, Robert Fitzroy, felt that Darwin was insufficiently qualified for the post, and hired someone else instead. However, Captain Fitzroy did consider Darwin for the position of "gentleman's companion" (someone with whom he could dine and talk who would be of his own social class). At first Fitzroy was reluctant, based on the shape of Darwin's head - Fitzroy was a believer in phrenology, the divining of a person's character and intellect by studying the shape and bumps on a person's head. However, Fitzroy eventually relented, and Darwin was taken on as Fitzroy's companion and amateur naturalist.


Darwin's five-year voyage aboard the Beagle transformed him from an indifferent student to a passionate and highly skilled naturalist. He had a natural talent for collecting specimens and recording his observations. He wrote volumes of notes and sent thousands of specimens back to museums in England. His noted eventually became the basis for his first book, A Journal of the Voyages of HMS Beagle, which he wrote with the encouragement of Captain Fitzroy upon his return to England, and which established his reputation as a naturalist among his colleagues.

However, Darwin was still essentially a creationist when he returned to England after the voyage of the Beagle. Upon his return, he started several notebooks in which he pondered the things he had observed while on the voyage. Within two years, he had become convinced that "descent with modification" had occurred, but he was at a loss as to how it happened. The crucial turning point in Darwin's thinking came on the evening of 28 September 1838, when he read Malthus' Essay on Population. This essay gave him the key to his theory: it suggested a mechanism by which "descent with modification" could occur. It was this mechanism that Darwin eventually called "natural selection" and which he made the basis of his theory of evolution.

Darwin's Conditions for Natural Selection


Understood correctly natural selection is not itself a mechanism. Rather, it is the outcome of the operation of three mechanisms:
Variety: There are always variations between the characteristics of the members of any population of living organisms.
These variations need not be extreme, as illustrated by the relatively large changes that animal and plant breeders have accomplished, using relatively slight differences in physical appearance and behavior among domestic animals and plants.

Heredity: The different variations noted above must be heritable from parents to offspring. Darwin couldn't propose a mechanism for such inheritance, as none was known at the time. Instead, he simply appealed to the common sense and experience of his readers, counting on them to grant that variations (however acquired) are generally heritable from parents to offspring.

Fecundity: Living organisms have a tendency to produce more offspring than can possibly survive.

Among those individuals that survive, those that also reproduce pass on to their offspring whatever characteristics made it possible for them to survive and reproduce. This was the missing piece in his theory that Darwin got from his reading of Malthus' essay on population.

Given these three pre-conditions, the following outcome is virtually inevitable:
Non-random, unequal survival and reproduction.
Survival and reproduction are almost never random. Instead, individuals survive and successfully reproduce at least partly as a result of their characteristics. It is these characteristics that provide the basis for evolutionary adaptations.

Darwin had no empirical (i.e. "observational") evidence for natural selection. Instead, he used imaginary examples and analogies to animal and plant breeding. In particular, he began to study the processes of animal and plant breeding very intensively, culminating in an essay that he wrote on the subject in 1842, which he later revised in 1844, and finally published as part of the Origin of Species in 1859.

Darwin began the Origin of Species by arguing that the various breeds of domesticated pigeons are analogous to the products of natural selection. He pointed out that all domesticated pigeon breeds are descendants of the wild rock dove (Columba livia). He went on to note that, although "[t]he diversity of the breeds is something astonishing…", they are not separate species. However, they are at least as different from each other as natural species are in the wild.

From his interviews with pigeon breeders, Darwin concluded that pigeon breeders of his time believed that all of the various breeds of pigeons were derived from separate kinds of pigeons that existed in the wild. That is, that no evolution or selection had taken place to produce such breeds. Darwin concluded otherwise: that all 700+ breeds of pigeons had been derived from the wild rock dove by means of artificial selection. He asserted that pigeon breeders were denying the evidence right in front of them: that their choices of breeding pairs were shaping the breeds that exist.
Darwin asserted that most of the artificial selection done by animal and plant breeders was probably done unconsciously, by breeders choosing desirable traits among their domesticated animals and plants.


Natural Selection and the Problem of Purpose in Nature

Darwin had two aims in writing the Origin of Species. The first was to convince his readers of the reality of "descent with modification" from common ancestors. He was largely successful in this aim.

To accomplish the first aim, Darwin presented an overwhelming mass of evidence from animal and plant breeding, animal behavior, paleontology, biogeography, comparative morphology, classification and taxonomy, and embryology, much of it newly acquired by naturalists from England and other European countries. Many of his readers were avid naturalists themselves, and followed Darwin's arguments and evidence to their obvious conclusion: that species had indeed changed over time.

In terms of the types of logical arguments we discussed in the previous lecture, Darwin's argument for descent with modification was essentially based on inductive reasoning. He presented multiple, independent, yet similar cases of observable phenomena, all pointing to the same conclusion: that species had gradually descended from previously existing species over long periods of time. Although the evidence could not absolutely prove that evolution had occurred, it was sufficient to convince most of the scientists of his time.

Darwin's second aim – which was much more important to Darwin himself – was to convince his readers that natural selection was the cause of the "beautiful adaptations" that largely define species. He was mostly unsuccessful in this aim.

To accomplish his second aim, Darwin was forced to use an argument from analogy, because he could not point to any real-world examples of natural selection in action. In the first chapter of the Origin of Species, he essentially argued that "breeds" under domestication are analogous to "species" in the wild insofar as both are shaped by selection. In other words:
Natural selection is analogous to artificial selection.

As I discussed in the previous chapter, arguments by analogy – while they are often used – are logically very weak. They depend fundamentally on the validity of the analogy, and are susceptible to subversion if another equally compelling analogy is presented. Historically, this was precisely what happened to Darwin's proposal of natural selection as the "engine" of descent with modification.

To understand why, recall our discussion of the concept of inference from the previous chapter, in which we considered an example of what looked like a house fire. Recall that you didn't actually witness the house fire. All you observed were its effects. What you are doing when you make a guess like this is inferring that an event that you have not actually observed has, in fact, taken place.

This is precisely what the theory of evolution does, and when you apply the theory to the natural world, you are using essentially the same reasoning that you would use to decide whether a house fire has happened along the road to work. Lacking direct evidence for natural selection, Darwin argued that its operation could be inferred from observable phenomena. He argued that natural selection is analogous to the artificial selection by which animal and plant breeders had developed the various characteristics of domesticated animals and plants. He also argued that most of this artificial selection had been conducted unintentionally (i.e unconsciously) by animal and plant breeders, thereby suggesting that natural selection could also operate without intentions or purposes.

In the Origin, Darwin tried to convince his readers of two propositions: that descent with modification had occurred, and that natural selection was the driving force behind it. Darwin's argument for descent with modification was based on inductive reasoning. He presented multiple, independent, yet similar cases of observable phenomena, all pointing to the same conclusion: that species had gradually descended from previously existing species over long periods of time. most scientific arguments are grounded in inductive reasoning, he was largely successful in convincing other scientists that descent with modification had occurred.

Darwin's argument for natural selection was largely based on analogy, primarily with artificial selection. Since natural selection was a new idea, there was virtually no actual evidence for or against it when the Origin was published. Instead, Darwin presented an essentially logical argument for natural selection, based on a few largely imaginary examples, and then encouraged his readers to accept the idea on that basis. In doing so, Darwin asked his readers to infer that natural selection was the most likely cause of the evolutionary changes he cited in his argument for descent with modification.

The great strength of Darwin's argument for descent with modification was the huge amount of evidence from natural history that he marshaled to support it. Arguments by induction, while not absolutely conclusive, are extremely powerful, especially in science. The greatest weakness of Darwin's argument for natural selection was the lack of empirical evidence he could site to support it. Arguments by analogy, while extremely common, have almost no logical force or validity, especially in science.

Darwin's argument for evolution by natural selection was a naturalistic argument. Like virtually all scientific arguments and explanations, it was based on the assumption that the only valid causes for observed effects were those that were entirely limited to natural objects and processes. Central to the naturalistic stance in science is the assumption that natural processes are not intentional; that is, they have no purpose and are not assumed to be the result of intelligent design. is one reason why scientists adopted Darwin's views so readily:

In the Origin of Species, Darwin presented the first fully naturalistic explanation for the evolution of life on Earth.

However, this is also why the theory of evolution by natural selection has met with such intense opposition by non-scientists, and especially religious believers; it ignores (and therefore implicitly negates) any possibility for intentional design or purpose in nature.

This conflict between the naturalistic viewpoint shared by virtually all scientists and the "intentional stance" so common among non-scientists (and especially religious believers) is nowhere more intense than in the field of evolutionary psychology. As we will see, evolutionary psychologists assume that much of human behavior is motivated by drives (and even physiological mechanisms) that are largely unconscious, and may even oppose what we perceive to be our conscious desires and intentions.

As just one example (which will be discussed in more detail in a later lecture), it has been widely observed that when couples divorce, the husband often remarries a woman much younger than himself, with whom he then has several children. Furthermore, this often happens despite the husband's lack of obvious intention to start a new family with his new wife. Social scientists often explain this behavior as stemming from economic or social causes, especially the economic disparity between men and women, which makes it much more likely for men to be able to support a new family than their ex-wives.

However, this explanation completely ignores the underlying motivations for this pattern of behavior, motivations that become clear only when one views this behavior from an evolutionary perspective. That is, the tendency for men to remarry women younger than themselves is most likely an evolutionary adaptation that is the result of the increased reproductive success that is the result of this behavior.

The idea that behaviors, including human behaviors, are evolutionary adaptations that are the result of natural selection is the basis for the science of evolutionary psychology. In the next lecture, therefore, we will take a closer look at what adaptations are and how they can be identified and distinguished from characteristics that are not the result of unequal, non-random survival and reproduction.

Essential Reading:

Darwin, C. (1859) On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life, 1st ed. John Murray. Available online here.


Supplemental Reading:

Barlow, N. (ed.) (1958) The autobiography of Charles Darwin, 1809-1882, with original omissions restored. Collins. Available online here.

Darwin, C. (1845) Journal of researches into the natural history and geology of the countries visited during the voyage of H.M.S. Beagle round the world, under the Command of Capt. Fitz Roy, R.N. 2d ed. John Murray. Available online here.

Darwin, C. (1871) The descent of man and selection in relation to sex, 1st ed. John Murray. Available online here.

Himmelfarb, G. (1959). Darwin and the darwinian revolution. Doubleday.

Malthus, R. T. (1798) An essay on the principle of population. J. Johnson. Available online here.

Questions to Consider:

1. Darwin is often credited with founding the science of biology with his publication of the Origin of Species in 1859. Why is this the case, and do you agree?

2. Darwin's theory of "descent with modification" was accepted by nearly all scientists within a decade of the publication of the Origin of Species in 1859. However, his proposed mechanism of natural selection was not nearly so widely accepted. Why not, and has this situation changed significantly today?

************************************************

As always, comments, criticisms, and suggestions are warmly welcomed!

--Allen
http://evolpsychology.blogspot.com/2008/09/natural-selection-darwins-dangerous.html

Evolution

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Part of the Biology series on
Evolution
Image of the tree of life showing genome size.
Mechanisms and processes

Adaptation
Genetic drift
Gene flow
Mutation
Natural selection
Speciation

Research and history

Introduction
Evidence
Evolutionary history of life
History
Modern synthesis
Social effect
Theory and fact
Objections / Controversy

Evolutionary biology fields

Cladistics
Ecological genetics
Evolutionary development
Human evolution
Molecular evolution
Phylogenetics
Population genetics

Biology portal · v  d  e 

In biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a process that can result in the emergence of new species.[1] The similarities among species suggest that all known species are descended from a common ancestor (or ancestral gene pool) through this process of gradual divergence.[2]

The basis of evolution is the genes that are passed on from generation to generation; these produce an organism's inherited traits. These traits vary within populations, with organisms showing heritable differences (variation) in their traits. Evolution itself is the product of two opposing forces: processes that constantly introduce variation, and processes that make variants either become more common or rare. New variation arises in two main ways: either from mutations in genes, or from the transfer of genes between populations and between species. New combinations of genes are also produced by genetic recombination, which can increase variation between organisms.

Two major mechanisms determine which variants will become more common or rare in a population. One is natural selection, a process that causes helpful traits (those that increase the chance of survival and reproduction) to become more common in a population and causes harmful traits to become more rare. This occurs because individuals with advantageous traits are more likely to reproduce, meaning that more individuals in the next generation will inherit these traits.[2][3] Over many generations, adaptations occur through a combination of successive, small, random changes in traits, and natural selection of the variants best-suited for their environment.[4] The other major mechanism driving evolution is genetic drift, an independent process that produces random changes in the frequency of traits in a population. Genetic drift results from the role that chance plays in whether a given trait will be passed on as individuals survive and reproduce.

Evolutionary biologists document the fact that evolution occurs, and also develop and test theories that explain its causes. The study of evolutionary biology began in the mid-nineteenth century, when research into the fossil record and the diversity of living organisms convinced most scientists that species changed over time.[5][6] However, the mechanism driving these changes remained unclear until the theories of natural selection were independently proposed by Charles Darwin and Alfred Wallace. Darwin's landmark 1859 work On the Origin of Species brought the new theories of evolution by natural selection to a wide audience,[7] leading to the overwhelming acceptance of evolution among scientists.[8][9][10][11] In the 1930s, Darwinian natural selection was combined with Mendelian inheritance to form the modern evolutionary synthesis,[12] which connected the units of evolution (genes) and the mechanism of evolution (natural selection). This powerful explanatory and predictive theory has become the central organizing principle of modern biology, directing research and providing a unifying explanation for the diversity of life on Earth.[9][10][13]

Contents

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Heredity

DNA structure. Bases are in the center, surrounded by phosphate–sugar chains in a double helix.

Evolution in organisms occurs through changes in heritable traits – particular characteristics of an organism. In humans, for example, eye color is an inherited characteristic, which individuals can inherit from one of their parents.[14] Inherited traits are controlled by genes and the complete set of genes within an organism's genome is called its genotype.[15]

The complete set of observable traits that make up the structure and behavior of an organism is called its phenotype. These traits come from the interaction of its genotype with the environment.[16] As a result, not every aspect of an organism's phenotype is inherited. Suntanned skin results from the interaction between a person's genotype and sunlight; thus, suntans are not passed on to people's children. However, people have different responses to sunlight, arising from differences in their genotype; a striking example is individuals with the inherited trait of albinism, who do not tan and are highly sensitive to sunburn.[17]

Heritable traits are passed from one generation to the next via DNA, a molecule that encodes genetic information.[15] DNA is a polymer composed of four types of bases. The sequence of bases along a particular DNA molecule specify the genetic information, in a manner similar to a sequence of letters specifying a sentence. Portions of a DNA molecule that specify a single functional unit are called genes; different genes have different sequences of bases. Within cells, the long strands of DNA form condensed structures called chromosomes. A specific location within a chromosome is known as a locus. If the DNA sequence at a locus varies between individuals, the different forms of this sequence are called alleles. DNA sequences can change through mutations, producing new alleles. If a mutation occurs within a gene, the new allele may affect the trait that the gene controls, altering the phenotype of the organism.

However, while this simple correspondence between an allele and a trait works in some cases, most traits are more complex and are controlled by multiple interacting genes.[18][19] The study of such complex traits is a major area of current genetic research. Another interesting but unsolved question in genetics is if epigenetics is important in evolution, this is where heritable changes occur in organisms without there being any changes to the sequences of their genes.[20]

Variation

An individual organism's phenotype results from both its genotype and the influence from the environment it has lived in. A substantial part of the variation in phenotypes in a population is caused by the differences between their genotypes.[19] The modern evolutionary synthesis defines evolution as the change over time in this genetic variation. The frequency of one particular allele will fluctuate, becoming more or less prevalent relative to other forms of that gene. Evolutionary forces act by driving these changes in allele frequency in one direction or another. Variation disappears when an allele reaches the point of fixation — when it either disappears from the population or replaces the ancestral allele entirely.[21]

Variation comes from mutations in genetic material, migration between populations (gene flow), and the reshuffling of genes through sexual reproduction. Variation also comes from exchanges of genes between different species; for example, through horizontal gene transfer in bacteria, and hybridization in plants.[22] Despite the constant introduction of variation through these processes, most of the genome of a species is identical in all individuals of that species.[23] However, even relatively small changes in genotype can lead to dramatic changes in phenotype: chimpanzees and humans differ in only about 5% of their genomes.[24]

Mutation

Duplication of part of a chromosome

Genetic variation comes from random mutations that occur in the genomes of organisms. Mutations are changes in the DNA sequence of a cell's genome and are caused by radiation, viruses, transposons and mutagenic chemicals, as well as errors that occur during meiosis or DNA replication.[25][26][27] These mutagens produce several different types of change in DNA sequences; these can either have no effect, alter the product of a gene, or prevent the gene from functioning. Studies in the fly Drosophila melanogaster suggest that if a mutation changes a protein produced by a gene, this will probably be harmful, with about 70 percent of these mutations having damaging effects, and the remainder being either neutral or weakly beneficial.[28] Due to the damaging effects that mutations can have on cells, organisms have evolved mechanisms such as DNA repair to remove mutations.[25] Therefore, the optimal mutation rate for a species is a trade-off between costs of a high mutation rate, such as deleterious mutations, and the metabolic costs of maintaining systems to reduce the mutation rate, such as DNA repair enzymes.[29] Viruses that use RNA as their genetic material have rapid mutation rates,[30] which can be an advantage since these viruses will evolve constantly and rapidly, and thus evade the defensive responses of e.g. the human immune system.[31]

Mutations can involve large sections of DNA becoming duplicated, usually through genetic recombination.[32] These duplications are a major source of raw material for evolving new genes, with tens to hundreds of genes duplicated in animal genomes every million years.[33] Most genes belong to larger families of genes of shared ancestry.[34] Novel genes are produced by several methods, commonly through the duplication and mutation of an ancestral gene, or by recombining parts of different genes to form new combinations with new functions.[35][36] Here, domains act as modules, each with a particular and independent function, that can be mixed together to produce genes encoding new proteins with novel properties.[37] For example, the human eye uses four genes to make structures that sense light: three for color vision and one for night vision; all four arose from a single ancestral gene.[38] Another advantage of duplicating a gene (or even an entire genome) is that this increases redundancy; this allows one gene in the pair to acquire a new function while the other copy performs the original function.[39][40] Other types of mutation occasionally create new genes from previously noncoding DNA.[41][42]

Changes in chromosome number may involve even larger mutations, where segments of the DNA within chromosomes break and then rearrange. For example, two chromosomes in the Homo genus fused to produce human chromosome 2; this fusion did not occur in the lineage of the other apes, and they retain these separate chromosomes.[43] In evolution, the most important role of such chromosomal rearrangements may be to accelerate the divergence of a population into new species by making populations less likely to interbreed, and thereby preserving genetic differences between these populations.[44]

Sequences of DNA that can move about the genome, such as transposons, make up a major fraction of the genetic material of plants and animals, and may have been important in the evolution of genomes.[45] For example, more than a million copies of the Alu sequence are present in the human genome, and these sequences have now been recruited to perform functions such as regulating gene expression.[46] Another effect of these mobile DNA sequences is that when they move within a genome, they can mutate or delete existing genes and thereby produce genetic diversity.[26]

Sex and recombination

In asexual organisms, genes are inherited together, or linked, as they cannot mix with genes in other organisms during reproduction. However, the offspring of sexual organisms contain random mixtures of their parents' chromosomes that are produced through independent assortment. In a related process called homologous recombination, sexual organisms exchange DNA between two matching chromosomes.[47] Recombination and reassortment do not alter allele frequencies, but instead change which alleles are associated with each other, producing offspring with new combinations of alleles.[48] Sex usually increases genetic variation and may increase the rate of evolution.[49][50] However, asexuality is advantageous in some environments as it can evolve in previously-sexual animals.[51] Here, asexuality might allow the two sets of alleles in their genome to diverge and gain different functions.[52]

Recombination allows even alleles that are close together in a strand of DNA to be inherited independently. However, the rate of recombination is low (approximately two events per chromosome per generation). As a result, genes close together on a chromosome may not always be shuffled away from each other, and genes that are close together tend to be inherited together, a phenomenon known as linkage.[53] This tendency is measured by finding how often two alleles occur together on a single chromosome, which is called their linkage disequilibrium. A set of alleles that is usually inherited in a group is called a haplotype. This can be important when one allele in a particular haplotype is strongly beneficial: natural selection can drive a selective sweep that will also cause the other alleles in the haplotype to become more common in the population; this effect is called genetic hitchhiking.[54]

When alleles cannot be separated by recombination – such as in mammalian Y chromosomes, which pass intact from fathers to sons – harmful mutations accumulate.[55][56] By breaking up allele combinations, sexual reproduction allows the removal of harmful mutations and the retention of beneficial mutations.[57] In addition, recombination and reassortment can produce individuals with new and advantageous gene combinations. These positive effects are balanced by the fact that sex reduces an organism's reproductive rate, can cause mutations and may separate beneficial combinations of genes.[57] The reasons for the evolution of sexual reproduction are therefore unclear and this question is still an active area of research in evolutionary biology,[58][59] that has prompted ideas such as the Red Queen hypothesis.[60]

Population genetics

 

From a genetic viewpoint, evolution is a generation-to-generation change in the frequencies of alleles within a population that shares a common gene pool.[61] A population is a localized group of individuals belonging to the same species. For example, all of the moths of the same species living in an isolated forest represent a population. A single gene in this population may have several alternate forms, which account for variations between the phenotypes of the organisms. An example might be a gene for coloration in moths that has two alleles: black and white. A gene pool is the complete set of alleles for a gene in a single population; the allele frequency measures the fraction of the gene pool composed of a single allele (for example, what fraction of moth coloration genes are the black allele). Evolution occurs when there are changes in the frequencies of alleles within a population of interbreeding organisms; for example, the allele for black color in a population of moths becoming more common.

To understand the mechanisms that cause a population to evolve, it is useful to consider what conditions are required for a population not to evolve. The Hardy-Weinberg principle states that the frequencies of alleles (variations in a gene) in a sufficiently large population will remain constant if the only forces acting on that population are the random reshuffling of alleles during the formation of the sperm or egg, and the random combination of the alleles in these sex cells during fertilization.[62] Such a population is said to be in Hardy-Weinberg equilibrium; it is not evolving.[63]

Gene flow

When they mature, male lions leave the pride where they were born and take over a new pride to mate, causing gene flow between prides.[64]

Gene flow is the exchange of genes between populations, which are usually of the same species.[65] Examples of gene flow within a species include the migration and then breeding of organisms, or the exchange of pollen. Gene transfer between species includes the formation of hybrid organisms and horizontal gene transfer.

Migration into or out of a population can change allele frequencies, as well as introducing genetic variation into a population. Immigration may add new genetic material to the established gene pool of a population. Conversely, emigration may remove genetic material. As barriers to reproduction between two diverging populations are required for the populations to become new species, gene flow may slow this process by spreading genetic differences between the populations. Gene flow is hindered by mountain ranges, oceans and deserts or even man-made structures such as the Great Wall of China, which has hindered the flow of plant genes.[66]

Depending on how far two species have diverged since their most recent common ancestor, it may still be possible for them to produce offspring, as with horses and donkeys mating to produce mules.[67] Such hybrids are generally infertile, due to the two different sets of chromosomes being unable to pair up during meiosis. In this case, closely related species may regularly interbreed, but hybrids will be selected against and the species will remain distinct. However, viable hybrids are occasionally formed and these new species can either have properties intermediate between their parent species, or possess a totally new phenotype.[68] The importance of hybridization in creating new species of animals is unclear, although cases have been seen in many types of animals,[69] with the gray tree frog being a particularly well-studied example.[70]

Hybridization is, however, an important means of speciation in plants, since polyploidy (having more than two copies of each chromosome) is tolerated in plants more readily than in animals.[71][72] Polyploidy is important in hybrids as it allows reproduction, with the two different sets of chromosomes each being able to pair with an identical partner during meiosis.[73] Polyploids also have more genetic diversity, which allows them to avoid inbreeding depression in small populations.[74]

Horizontal gene transfer is the transfer of genetic material from one organism to another organism that is not its offspring; this is most common among bacteria.[75] In medicine, this contributes to the spread of antibiotic resistance, as when one bacteria acquires resistance genes it can rapidly transfer them to other species.[76] Horizontal transfer of genes from bacteria to eukaryotes such as the yeast Saccharomyces cerevisiae and the adzuki bean beetle Callosobruchus chinensis may also have occurred.[77][78] An example of larger-scale transfers are the eukaryotic bdelloid rotifers, which appear to have received a range of genes from bacteria, fungi, and plants.[79] Viruses can also carry DNA between organisms, allowing transfer of genes even across biological domains.[80] Large-scale gene transfer has also occurred between the ancestors of eukaryotic cells and prokaryotes, during the acquisition of chloroplasts and mitochondria.[81]

Mechanisms

The two main mechanisms that produce evolution are natural selection and genetic drift. Natural selection favors genes that improve capacity for survival and reproduction. Genetic drift is random change in the frequency of alleles, caused by the random sampling of a generation's genes during reproduction. The relative importance of natural selection and genetic drift in a population varies depending on the strength of the selection and the effective population size, which is the number of individuals capable of breeding.[82] Natural selection usually predominates in large populations, while genetic drift dominates in small populations. The dominance of genetic drift in small populations can even lead to the fixation of slightly deleterious mutations.[83] As a result, changing population size can dramatically influence the course of evolution. Population bottlenecks, where the population shrinks temporarily and therefore loses genetic variation, result in a more uniform population.[21]

Natural selection

Natural selection of a population for dark coloration.

Natural selection is the process by which genetic mutations that enhance reproduction become, and remain, more common in successive generations of a population. It has often been called a "self-evident" mechanism because it necessarily follows from three simple facts:

  • Heritable variation exists within populations of organisms.
  • Organisms produce more offspring than can survive.
  • These offspring vary in their ability to survive and reproduce.

These conditions produce competition between organisms for survival and reproduction. Consequently, organisms with traits that give them an advantage over their competitors pass these advantageous traits on, while traits that do not confer an advantage are not passed on to the next generation.[84]

The central concept of natural selection is the evolutionary fitness of an organism.[85] Fitness is measured by an organism's ability to survive and reproduce, which determines the size of its genetic contribution to the next generation.[85] However, fitness is not the same as the total number of offspring: instead fitness is indicated by the proportion of subsequent generations that carry an organism's genes.[86] For example, if an organism could survive well and reproduce rapidly, but its offspring were all too small and weak to survive, this organism would make little genetic contribution to future generations and would thus have low fitness.[85]

If an allele increases fitness more than the other alleles of that gene, then with each generation this allele will become more common within the population. These traits are said to be "selected for". Examples of traits that can increase fitness are enhanced survival, and increased fecundity. Conversely, the lower fitness caused by having a less beneficial or deleterious allele results in this allele becoming rarer — they are "selected against".[3] Importantly, the fitness of an allele is not a fixed characteristic, if the environment changes, previously neutral or harmful traits may become beneficial and previously beneficial traits become harmful.[2] However, even if the direction of selection does reverse in this way, traits that were lost in the past may not re-evolve in an identical form (see Dollo's law).[87][88]

Natural selection within a population for a trait that can vary across a range of values, such as height, can be categorized into three different types. The first is directional selection, which is a shift in the average value of a trait over time — for example organisms slowly getting taller.[89] Secondly, disruptive selection is selection for extreme trait values and often results in two different values becoming most common, with selection against the average value. This would be when either short or tall organisms had an advantage, but not those of medium height. Finally, in stabilizing selection there is selection against extreme trait values on both ends, which causes a decrease in variance around the average value and less diversity.[84][90] This would, for example, cause organisms to slowly become all the same height.

A special case of natural selection is sexual selection, which is selection for any trait that increases mating success by increasing the attractiveness of an organism to potential mates.[91] Traits that evolved through sexual selection are particularly prominent in males of some animal species, despite traits such as cumbersome antlers, mating calls or bright colors that attract predators, decreasing the survival of individual males.[92] This survival disadvantage is balanced by higher reproductive success in males that show these hard to fake, sexually selected traits.[93]

Natural selection most generally makes nature the measure against which individuals, and individual traits, are more or less likely to survive. "Nature" in this sense refers to an ecosystem, that is, a system in which organisms interact with every other element, physical as well as biological, in their local environment. Eugene Odum, a founder of ecology, defined an ecosystem as: "Any unit that includes all of the organisms...in a given area interacting with the physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity, and material cycles (ie: exchange of materials between living and nonliving parts) within the system."[94] Each population within an ecosystem occupies a distinct niche, or position, with distinct relationships to other parts of the system. These relationships involve the life history of the organism, its position in the food chain, and its geographic range. This broad understanding of nature enables scientists to delineate specific forces which, together, comprise natural selection.

An active area of research is the unit of selection, with natural selection being proposed to work at the level of genes, cells, individual organisms, groups of organisms and even species.[95][96] None of these are mutually exclusive and selection may act on multiple levels simultaneously.[97] An example of selection occurring below the level of the individual organism are genes called transposons, which can replicate and spread throughout a genome.[98] Selection at a level above the individual, such as group selection, may allow the evolution of co-operation, as discussed below.[99]

Genetic drift

Simulation of genetic drift of 20 unlinked alleles in populations of 10 (top) and 100 (bottom). Drift to fixation is more rapid in the smaller population.

Genetic drift is the change in allele frequency from one generation to the next that occurs because alleles in offspring are a random sample of those in the parents, as well as from the role that chance plays in determining whether a given individual will survive and reproduce. In mathematical terms, alleles are subject to sampling error. As a result, when selective forces are absent or relatively weak, allele frequencies tend to "drift" upward or downward randomly (in a random walk). This drift halts when an allele eventually becomes fixed, either by disappearing from the population, or replacing the other alleles entirely. Genetic drift may therefore eliminate some alleles from a population due to chance alone. Even in the absence of selective forces, genetic drift can cause two separate populations that began with the same genetic structure to drift apart into two divergent populations with different sets of alleles.[100]

The time for an allele to become fixed by genetic drift depends on population size, with fixation occurring more rapidly in smaller populations.[101] The precise measure of population that is important is called the effective population size. The effective population is always smaller than the total population since it takes into account factors such as the level of inbreeding, the number of animals that are too old or young to breed, and the lower probability of animals that live far apart managing to mate with each other.[102]

An example when genetic drift is probably of central importance in determining a trait is the loss of pigments from animals that live in caves, a change that produces no obvious advantage or disadvantage in complete darkness.[103] However, it is usually difficult to measure the relative importance of selection and drift,[104] so the comparative importance of these two forces in driving evolutionary change is an area of current research.[105] These investigations were prompted by the neutral theory of molecular evolution, which proposed that most evolutionary changes are the result of the fixation of neutral mutations that do not have any immediate effects on the fitness of an organism.[106] Hence, in this model, most genetic changes in a population are the result of constant mutation pressure and genetic drift.[107] This form of the neutral theory is now largely abandoned, since it does not seem to fit the genetic variation seen in nature.[108][109] However, a more recent and better-supported version of this model is the nearly neutral theory, where most mutations only have small effects on fitness.[84]

Outcomes

Evolution influences every aspect of the form and behavior of organisms. Most prominent are the specific behavioral and physical adaptations that are the outcome of natural selection. These adaptations increase fitness by aiding activities such as finding food, avoiding predators or attracting mates. Organisms can also respond to selection by co-operating with each other, usually by aiding their relatives or engaging in mutually beneficial symbiosis. In the longer term, evolution produces new species through splitting ancestral populations of organisms into new groups that cannot or will not interbreed.

These outcomes of evolution are sometimes divided into macroevolution, which is evolution that occurs at or above the level of species, such as extinction and speciation, and microevolution, which is smaller evolutionary changes, such as adaptations, within a species or population.[110] In general, macroevolution is regarded as the outcome of long periods of microevolution.[111] Thus, the distinction between micro- and macroevolution is not a fundamental one - the difference is simply the time involved.[112] However, in macroevolution, the traits of the entire species may be important. For instance, a large amount of variation among individuals allows a species to rapidly adapt to new habitats, lessening the chance of it going extinct, while a wide geographic range increases the chance of speciation, by making it more likely that part of the population will become isolated. In this sense, microevolution and macroevolution might involve selection at different levels - with microevolution acting on genes and organisms, versus macroevolutionary processes acting on entire species and affecting the rate of speciation and extinction.[113][114][115]

A common misconception is that evolution has goals or long-term plans, but in reality, evolution has no long-term goal and does not necessarily produce greater complexity.[116][117] Although complex species have evolved, this occurs as a side effect of the overall number of organisms increasing, and simple forms of life remain more common.[118] For example, the overwhelming majority of species are microscopic prokaryotes, which form about half the world's biomass despite their small size,[119] and constitute the vast majority of Earth's biodiversity.[120] Simple organisms have therefore been the dominant form of life on Earth throughout its history and continue to be the main form of life up to the present day, with complex life only appearing more diverse because it is more noticeable.[121] Indeed, the evolution of microorganisms is particularly important to modern evolutionary research, since their rapid reproduction allows the study of experimental evolution and the observation of evolution and adaptation in real time.[122][123]

Adaptation

Adaptation is one of the basic phenomena of biology,[124] and is the process whereby an organism becomes better suited to its habitat.[125][126] Also, the term adaptation may refer to a trait that is important for an organism's survival. For example, the adaptation of horses' teeth to the grinding of grass, or the ability of horses to run fast and escape predators. By using the term adaptation for the evolutionary process, and adaptive trait for the product (the bodily part or function), the two senses of the word may be distinguished. Adaptations are produced by natural selection.[127] The following definitions are due to Theodosius Dobzhansky.

1. Adaptation is the evolutionary process whereby an organism becomes better able to live in its habitat or habitats.[128]2. Adaptedness is the state of being adapted: the degree to which an organism is able to live and reproduce in a given set of habitats.[129]3. An adaptive trait is an aspect of the developmental pattern of the organism which enables or enhances the probability of that organism surviving and reproducing.[130]

Adaptation may cause either the gain of a new feature, or the loss of an ancestral feature. An example that shows both types of change is bacterial adaptation to antibiotic selection, with genetic changes causing antibiotic resistance by both modifying the target of the drug, or increasing the activity of transporters that pump the drug out of the cell.[131] Other striking examples are the bacteria Escherichia coli evolving the ability to use citric acid as a nutrient in a long-term laboratory experiment,[132] Flavobacterium evolving a novel enzyme that allows these bacteria to grow on the by-products of nylon manufacturing,[133][134] and the soil bacterium Sphingobium evolving an entirely new metabolic pathway that degrades the synthetic pesticide pentachlorophenol.[135][136] An interesting but still controversial idea is that some adaptations might increase the ability of organisms to generate genetic diversity and adapt by natural selection (increasing organisms' evolvability).[137][138]

A baleen whale skeleton, a and b label flipper bones, which were adapted from front leg bones: while c indicates vestigial leg bones.[139]

Adaptation occurs through the gradual modification of existing structures. Consequently, structures with similar internal organization may have different functions in related organisms. This is the result of a single ancestral structure being adapted to function in different ways. The bones within bat wings, for example, are very similar to those in mice feet and primate hands, due to the descent of all these structures from a common mammalian ancestor.[140] However, since all living organisms are related to some extent,[141] even organs that appear to have little or no structural similarity, such as arthropod, squid and vertebrate eyes, or the limbs and wings of arthropods and vertebrates, can depend on a common set of homologous genes that control their assembly and function; this is called deep homology.[142][143]

During adaptation, some structures may lose their original function and become vestigial structures.[144] Such structures may have little or no function in a current species, yet have a clear function in ancestral species, or other closely related species. Examples include pseudogenes,[145] the non-functional remains of eyes in blind cave-dwelling fish,[146] wings in flightless birds,[147] and the presence of hip bones in whales and snakes.[139] Examples of vestigial structures in humans include wisdom teeth,[148] the coccyx,[144] and the vermiform appendix.[144]

However, many traits that appear to be simple adaptations are in fact exaptations: structures originally adapted for one function, but which coincidentally became somewhat useful for some other function in the process.[149] One example is the African lizard Holaspis guentheri, which developed an extremely flat head for hiding in crevices, as can be seen by looking at its near relatives. However, in this species, the head has become so flattened that it assists in gliding from tree to tree—an exaptation.[149] Within cells, molecular machines such as the bacterial flagella[150] and protein sorting machinery[151] evolved by the recruitment of several pre-existing proteins that previously had different functions.[110] Another example is the recruitment of enzymes from glycolysis and xenobiotic metabolism to serve as structural proteins called crystallins within the lenses of organisms' eyes.[152][153]

A critical principle of ecology is that of competitive exclusion: no two species can occupy the same niche in the same environment for a long time.[154] Consequently, natural selection will tend to force species to adapt to different ecological niches. This may mean that, for example, two species of cichlid fish adapt to live in different habitats, which will minimize the competition between them for food.[155]

An area of current investigation in evolutionary developmental biology is the developmental basis of adaptations and exaptations.[156] This research addresses the origin and evolution of embryonic development and how modifications of development and developmental processes produce novel features.[157] These studies have shown that evolution can alter development to create new structures, such as embryonic bone structures that develop into the jaw in other animals instead forming part of the middle ear in mammals.[158] It is also possible for structures that have been lost in evolution to reappear due to changes in developmental genes, such as a mutation in chickens causing embryos to grow teeth similar to those of crocodiles.[159] It is now becoming clear that most alterations in the form of organisms are due to changes in a small set of conserved genes.[160]

Co-evolution

Interactions between organisms can produce both conflict and co-operation. When the interaction is between pairs of species, such as a pathogen and a host, or a predator and its prey, these species can develop matched sets of adaptations. Here, the evolution of one species causes adaptations in a second species. These changes in the second species then, in turn, cause new adaptations in the first species. This cycle of selection and response is called co-evolution.[161] An example is the production of tetrodotoxin in the rough-skinned newt and the evolution of tetrodotoxin resistance in its predator, the common garter snake. In this predator-prey pair, an evolutionary arms race has produced high levels of toxin in the newt and correspondingly high levels of resistance in the snake.[162]

Co-operation

However, not all interactions between species involve conflict.[163] Many cases of mutually beneficial interactions have evolved. For instance, an extreme cooperation exists between plants and the mycorrhizal fungi that grow on their roots and aid the plant in absorbing nutrients from the soil.[164] This is a reciprocal relationship as the plants provide the fungi with sugars from photosynthesis. Here, the fungi actually grow inside plant cells, allowing them to exchange nutrients with their hosts, while sending signals that suppress the plant immune system.[165]

Coalitions between organisms of the same species have also evolved. An extreme case is the eusociality found in social insects, such as bees, termites and ants, where sterile insects feed and guard the small number of organisms in a colony that are able to reproduce. On an even smaller scale, the somatic cells that make up the body of an animal limit their reproduction so they can maintain a stable organism, which then supports a small number of the animal's germ cells to produce offspring. Here, somatic cells respond to specific signals that instruct them whether to grow, remain as they are, or die. If cells ignore these signals and multiply inappropriately, their uncontrolled growth causes cancer.[25]

These examples of cooperation within species are thought to have evolved through the process of kin selection, which is where one organism acts to help raise a relative's offspring.[166] This activity is selected for because if the helping individual contains alleles which promote the helping activity, it is likely that its kin will also contain these alleles and thus those alleles will be passed on.[167] Other processes that may promote cooperation include group selection, where cooperation provides benefits to a group of organisms.[168]

Speciation

The four mechanisms of speciation.

Speciation is the process where a species diverges into two or more descendant species.[169] Evolutionary biologists view species as statistical phenomena and not categories or types. This view is counterintuitive since the classical idea of species is still widely held, with a species seen as a class of organisms exemplified by a "type specimen" that bears all the traits common to this species. Instead, a species is now defined as a separately evolving lineage that forms a single gene pool. Although properties such as genetics and morphology are used to help separate closely related lineages, this definition has fuzzy boundaries.[170] Indeed, the exact definition of the term "species" is still controversial, particularly in prokaryotes,[171] and this is called the species problem.[172] Biologists have proposed a range of more precise definitions, but the definition used is a pragmatic choice that depends on the particularities of the species concerned.[172] Typically the actual focus on biological study is the population, an observable interacting group of organisms, rather than a species, an observable similar group of individuals.

Speciation has been observed multiple times under both controlled laboratory conditions and in nature.[173] In sexually reproducing organisms, speciation results from reproductive isolation followed by genealogical divergence. There are four mechanisms for speciation. The most common in animals is allopatric speciation, which occurs in populations initially isolated geographically, such as by habitat fragmentation or migration. Selection under these conditions can produce very rapid changes in the appearance and behaviour of organisms.[174][175] As selection and drift act independently on populations isolated from the rest of their species, separation may eventually produce organisms that cannot interbreed.[176]

The second mechanism of speciation is peripatric speciation, which occurs when small populations of organisms become isolated in a new environment. This differs from allopatric speciation in that the isolated populations are numerically much smaller than the parental population. Here, the founder effect causes rapid speciation through both rapid genetic drift and selection on a small gene pool.[177]

The third mechanism of speciation is parapatric speciation. This is similar to peripatric speciation in that a small population enters a new habitat, but differs in that there is no physical separation between these two populations. Instead, speciation results from the evolution of mechanisms that reduce gene flow between the two populations.[169] Generally this occurs when there has been a drastic change in the environment within the parental species' habitat. One example is the grass Anthoxanthum odoratum, which can undergo parapatric speciation in response to localized metal pollution from mines.[178] Here, plants evolve that have resistance to high levels of metals in the soil. Selection against interbreeding with the metal-sensitive parental population produced a gradual change in the flowering time of the metal-resistant plants, which eventually produced complete reproductive isolation. Selection against hybrids between the two populations may cause reinforcement, which is the evolution of traits that promote mating within a species, as well as character displacement, which is when two species become more distinct in appearance.[179]

Geographical isolation of finches on the Galápagos Islands produced over a dozen new species.

Finally, in sympatric speciation species diverge without geographic isolation or changes in habitat. This form is rare since even a small amount of gene flow may remove genetic differences between parts of a population.[180] Generally, sympatric speciation in animals requires the evolution of both genetic differences and non-random mating, to allow reproductive isolation to evolve.[181]

One type of sympatric speciation involves cross-breeding of two related species to produce a new hybrid species. This is not common in animals as animal hybrids are usually sterile. This is because during meiosis the homologous chromosomes from each parent are from different species and cannot successfully pair. However, it is more common in plants because plants often double their number of chromosomes, to form polyploids.[182] This allows the chromosomes from each parental species to form a matching pair during meiosis, since as each parent's chromosomes is represented by a pair already.[183] An example of such a speciation event is when the plant species Arabidopsis thaliana and Arabidopsis arenosa cross-bred to give the new species Arabidopsis suecica.[184] This happened about 20,000 years ago,[185] and the speciation process has been repeated in the laboratory, which allows the study of the genetic mechanisms involved in this process.[186] Indeed, chromosome doubling within a species may be a common cause of reproductive isolation, as half the doubled chromosomes will be unmatched when breeding with undoubled organisms.[72]

Speciation events are important in the theory of punctuated equilibrium, which accounts for the pattern in the fossil record of short "bursts" of evolution interspersed with relatively long periods of stasis, where species remain relatively unchanged.[187] In this theory, speciation and rapid evolution are linked, with natural selection and genetic drift acting most strongly on organisms undergoing speciation in novel habitats or small populations. As a result, the periods of stasis in the fossil record correspond to the parental population, and the organisms undergoing speciation and rapid evolution are found in small populations or geographically restricted habitats, and therefore rarely being preserved as fossils.[188]

Extinction

Extinction is the disappearance of an entire species. Extinction is not an unusual event, as species regularly appear through speciation, and disappear through extinction.[189] Nearly all animal and plant species that have lived on earth are now extinct,[190] and extinction appears to be the ultimate fate of all species.[191] These extinctions have happened continuously throughout the history of life, although the rate of extinction spikes in occasional mass extinction events.[192] The Cretaceous–Tertiary extinction event, during which the non-avian dinosaurs went extinct, is the most well-known, but the earlier Permian–Triassic extinction event was even more severe, with approximately 96 percent of species driven to extinction.[192] The Holocene extinction event is an ongoing mass extinction associated with humanity's expansion across the globe over the past few thousand years. Present-day extinction rates are 100-1000 times greater than the background rate, and up to 30 percent of species may be extinct by the mid 21st century.[193] Human activities are now the primary cause of the ongoing extinction event;[194] global warming may further accelerate it in the future.[195]

The role of extinction in evolution is not very well understood and may depend on which type of extinction is considered.[192] The causes of the continuous "low-level" extinction events, which form the majority of extinctions, may be the result of competition between species for limited resources (competitive exclusion).[12] If one species can out-compete another, this could produce species selection, with the fitter species surviving and the other species being driven to extinction.[95] The intermittent mass extinctions are also important, but instead of acting as a selective force, they drastically reduce diversity in a nonspecific manner and promote bursts of rapid evolution and speciation in survivors.[196]

Evolutionary history of life

Origin of life

The origin of life is a necessary precursor for biological evolution, but understanding that evolution occurred once organisms appeared and investigating how this happens does not depend on understanding exactly how life began.[197] The current scientific consensus is that the complex biochemistry that makes up life came from simpler chemical reactions, but it is unclear how this occurred.[198] Not much is certain about the earliest developments in life, the structure of the first living things, or the identity and nature of any last universal common ancestor or ancestral gene pool.[199][200] Consequently, there is no scientific consensus on how life began, but proposals include self-replicating molecules such as RNA,[201] and the assembly of simple cells.[202]

Common descent

The hominoids are descendants of a common ancestor.

All organisms on Earth are descended from a common ancestor or ancestral gene pool.[141] Current species are a stage in the process of evolution, with their diversity the product of a long series of speciation and extinction events.[203] The common descent of organisms was first deduced from four simple facts about organisms: First, they have geographic distributions that cannot be explained by local adaptation. Second, the diversity of life is not a set of completely unique organisms, but organisms that share morphological similarities. Third, vestigial traits with no clear purpose resemble functional ancestral traits, and finally, that organisms can be classified using these similarities into a hierarchy of nested groups - similar to a family tree.[7] However, modern research has suggested that, due to horizontal gene transfer, this "tree of life" may be more complicated than a simple branching tree since some genes have spread independently between distantly related species.[204][205]

Past species have also left records of their evolutionary history. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical, record.[206] By comparing the anatomies of both modern and extinct species, paleontologists can infer the lineages of those species. However, this approach is most successful for organisms that had hard body parts, such as shells, bones or teeth. Further, as prokaryotes such as bacteria and archaea share a limited set of common morphologies, their fossils do not provide information on their ancestry.

More recently, evidence for common descent has come from the study of biochemical similarities between organisms. For example, all living cells use the same basic set of nucleotides and amino acids.[207] The development of molecular genetics has revealed the record of evolution left in organisms' genomes: dating when species diverged through the molecular clock produced by mutations.[208] For example, these DNA sequence comparisons have revealed the close genetic similarity between humans and chimpanzees and shed light on when the common ancestor of these species existed.[209]

Evolution of life

Evolutionary tree showing the divergence of modern species from their common ancestor in the center.[210] The three domains are colored, with bacteria blue, archaea green, and eukaryotes red.

Despite the uncertainty on how life began, it is generally accepted that prokaryotes inhabited the Earth from approximately 3–4 billion years ago.[211][212] No obvious changes in morphology or cellular organization occurred in these organisms over the next few billion years.[213]

The eukaryotes were the next major change in cell structure. These came from ancient bacteria being engulfed by the ancestors of eukaryotic cells, in a cooperative association called endosymbiosis.[81][214] The engulfed bacteria and the host cell then underwent co-evolution, with the bacteria evolving into either mitochondria or hydrogenosomes.[215] An independent second engulfment of cyanobacterial-like organisms led to the formation of chloroplasts in algae and plants.[216] It is unknown when the first eukaryotic cells appeared though they first emerged between 1.6 - 2.7 billion years ago.

The history of life was that of the unicellular eukaryotes, prokaryotes, and archaea until about 610 million years ago when multicellular organisms began to appear in the oceans in the Ediacaran period.[211][217] The evolution of multicellularity occurred in multiple independent events, in organisms as diverse as sponges, brown algae, cyanobacteria, slime moulds and myxobacteria.[218]

Soon after the emergence of these first multicellular organisms, a remarkable amount of biological diversity appeared over approximately 10 million years, in an event called the Cambrian explosion. Here, the majority of types of modern animals appeared in the fossil record, as well as unique lineages that subsequently became extinct.[219] Various triggers for the Cambrian explosion have been proposed, including the accumulation of oxygen in the atmosphere from photosynthesis.[220] About 500 million years ago, plants and fungi colonized the land, and were soon followed by arthropods and other animals.[221] Amphibians first appeared around 300 million years ago, followed by early amniotes, then mammals around 200 million years ago and birds around 100 million years ago (both from "reptile"-like lineages). However, despite the evolution of these large animals, smaller organisms similar to the types that evolved early in this process continue to be highly successful and dominate the Earth, with the majority of both biomass and species being prokaryotes.[120]

History of evolutionary thought

Charles Darwin at age 51, just after publishing On the Origin of Species.

Evolutionary ideas such as common descent and the transmutation of species have existed since at least the 6th century BCE, when they were expounded by the Greek philosopher Anaximander.[222] Others who considered such ideas included the Greek philosopher Empedocles, the Roman philosopher-poet Lucretius, the Arab biologist Al-Jahiz,[223] the Persian philosopher Ibn Miskawayh, the Brethren of Purity,[224] and the Chinese philosopher Zhuangzi.[225] As biological knowledge grew in the 18th century, evolutionary ideas were set out by a few natural philosophers including Pierre Maupertuis in 1745 and Erasmus Darwin in 1796.[226] The ideas of the biologist Jean-Baptiste Lamarck about transmutation of species had wide influence. Charles Darwin formulated his idea of natural selection in 1838 and was still developing his theory in 1858 when Alfred Russel Wallace sent him a similar theory, and both were presented to the Linnean Society of London in separate papers.[227] At the end of 1859 Darwin's publication of On the Origin of Species explained natural selection in detail and presented evidence leading to increasingly wide acceptance of the occurrence of evolution.

Debate about the mechanisms of evolution continued, and Darwin could not explain the source of the heritable variations which would be acted on by natural selection. Like Lamarck, he thought that parents passed on adaptations acquired during their lifetimes,[228] a theory which was subsequently dubbed Lamarckism.[229] In the 1880s August Weismann's experiments indicated that changes from use and disuse were not heritable, and Lamarckism gradually fell from favour.[230][231] More significantly, Darwin could not account for how traits were passed down from generation to generation. In 1865 Gregor Mendel found that traits were inherited in a predictable manner.[232] When Mendel's work was rediscovered in 1900s, disagreements over the rate of evolution predicted by early geneticists and biometricians led to a rift between the Mendelian and Darwinian models of evolution.

Yet it was the rediscovery of Gregor Mendel's pioneering work on the fundamentals of genetics (of which Darwin and Wallace were unaware) by Hugo de Vries and others in the early 1900s that provided the impetus for a better understanding of how variation occurs in plant and animal traits. That variation is the main fuel used by natural selection to shape the wide variety of adaptive traits observed in organic life. Even though Hugo de Vries and other early geneticists rejected gradual natural selection, their rediscovery of and subsequent work on genetics eventually provided a solid basis on which the theory of evolution stood even more convincingly than when it was originally proposed.[233]

The apparent contradiction between Darwin's theory of evolution by natural selection and Mendel's work was reconciled in the 1920s and 1930s by evolutionary biologists such as J.B.S. Haldane, Sewall Wright, and particularly Ronald Fisher, who set the foundations for the establishment of the field of population genetics. The end result was a combination of evolution by natural selection and Mendelian inheritance, the modern evolutionary synthesis.[234] In the 1940s, the identification of DNA as the genetic material by Oswald Avery and colleagues and the subsequent publication of the structure of DNA by James Watson and Francis Crick in 1953, demonstrated the physical basis for inheritance. Since then, genetics and molecular biology have become core parts of evolutionary biology and have revolutionized the field of phylogenetics.[12]

In its early history, evolutionary biology primarily drew in scientists from traditional taxonomically oriented disciplines, whose specialist training in particular organisms addressed general questions in evolution. As evolutionary biology expanded as an academic discipline, particularly after the development of the modern evolutionary synthesis, it began to draw more widely from the biological sciences.[12] Currently the study of evolutionary biology involves scientists from fields as diverse as biochemistry, ecology, genetics and physiology, and evolutionary concepts are used in even more distant disciplines such as psychology, medicine, philosophy and computer science. In the 21st century, current research in evolutionary biology deals with several areas where the modern evolutionary synthesis may need modification or extension, such as assessing the relative importance of various ideas on the unit of selection and evolvability and how to fully incorporate the findings of evolutionary developmental biology.[235][236]

Social and cultural responses

As Darwinism became widely accepted in the 1870s, caricatures of Charles Darwin with a quadrupedal ape or monkey body symbolised evolution.[237]

In the 19th century, particularly after the publication of On the Origin of Species in 1859, the idea that life had evolved was an active source of academic debate centered on the philosophical, social and religious implications of evolution. Nowadays, the fact that organisms evolve is uncontested in the scientific literature and the modern evolutionary synthesis is widely accepted by scientists.[12] However, evolution remains a contentious concept for some theists.[238]

While various religions and denominations have reconciled their beliefs with evolution through concepts such as theistic evolution, there are creationists who believe that evolution is contradicted by the creation myths found in their respective religions and who raise various objections to evolution.[110][239][240] As had been demonstrated by responses to the publication of Vestiges of the Natural History of Creation in 1844, the most controversial aspect of evolutionary biology is the implication of human evolution that human mental and moral faculties, which had been thought purely spiritual, are not distinctly separated from those of other animals.[6] In some countries—notably the United States—these tensions between science and religion have fueled the current creation-evolution controversy, a religious conflict focusing on politics and public education.[241] While other scientific fields such as cosmology[242] and earth science[243] also conflict with literal interpretations of many religious texts, evolutionary biology experiences significantly more opposition from religious literalists.

Another example associated with evolutionary theory that is now widely regarded as unwarranted is misnamed "Social Darwinism," a term given to the 19th century Whig Malthusian theory developed by Herbert Spencer into ideas about "survival of the fittest" in commerce and human societies as a whole, and by others into claims that social inequality, sexism, racism, and imperialism were justified.[244] However, these ideas contradict Darwin's own views, and contemporary scientists and philosophers consider these ideas to be neither mandated by evolutionary theory nor supported by data.[245][246][247]

The teaching of evolution in American secondary school biology classes was uncommon in most of the first half of the 20th century. The Scopes Trial decision of 1925 caused the subject to become very rare in American secondary biology textbooks for a generation, but it was gradually re-introduced about a generation later and legally protected with the 1968 Epperson v. Arkansas decision. Since then, the competing religious belief of creationism was legally disallowed in secondary school curricula in various decisions in the 1970s and 1980s, but it returned in the form of intelligent design, to be excluded once again in the 2005 Kitzmiller v. Dover Area School District case.[248]

Applications

Evolutionary biology, and in particular the understanding of how organisms evolve through natural selection, is an area of science with many practical applications.[249] A major technological application of evolution is artificial selection, which is the intentional selection of certain traits in a population of organisms. Humans have used artificial selection for thousands of years in the domestication of plants and animals.[250] More recently, such selection has become a vital part of genetic engineering, with selectable markers such as antibiotic resistance genes being used to manipulate DNA in molecular biology. It is also possible to use repeated rounds of mutation and selection to evolve proteins with particular properties, such as modified enzymes or new antibodies, in a process called directed evolution.[251]

Understanding the changes that have occurred during organism's evolution can reveal the genes needed to construct parts of the body, genes which may be involved in human genetic disorders.[252] For example, the Mexican tetra is an albino cavefish that lost its eyesight during evolution. Breeding together different populations of this blind fish produced some offspring with functional eyes, since different mutations had occurred in the isolated populations that had evolved in different caves.[253] This helped identify genes required for vision and pigmentation, such as crystallins and the melanocortin 1 receptor.[254] Similarly, comparing the genome of the Antarctic icefish, which lacks red blood cells, to close relatives such as the zebrafish revealed genes needed to make these blood cells.[255]

As evolution can produce highly optimized processes and networks, it has many applications in computer science. Here, simulations of evolution using evolutionary algorithms and artificial life started with the work of Nils Aall Barricelli in the 1960s, and was extended by Alex Fraser, who published a series of papers on simulation of artificial selection.[256] Artificial evolution became a widely recognized optimization method as a result of the work of Ingo Rechenberg in the 1960s and early 1970s, who used evolution strategies to solve complex engineering problems.[257] Genetic algorithms in particular became popular through the writing of John Holland.[258] As academic interest grew, dramatic increases in the power of computers allowed practical applications, including the automatic evolution of computer programs.[259] Evolutionary algorithms are now used to solve multi-dimensional problems more efficiently than software produced by human designers, and also to optimize the design of systems.[260]

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