From the NYT:
Scientists Square Off on Evolutionary Value of Helping Relatives
By CARL ZIMMER
Why are worker ants sterile? Why do birds sometimes help their parents raise more chicks, instead of having chicks of their own? Why do bacteria explode with toxins to kill rival colonies? In 1964, the British biologist William Hamilton published a landmark paper to answer these kinds of questions. Sometimes, he argued, helping your relatives can spread your genes faster than having children of your own.
For the past 46 years, biologists have used Dr. Hamilton’s theory to make sense of how animal societies evolve. They’ve even applied it to the evolution of our own species. But in the latest issue of the journal Nature, a team of prominent evolutionary biologists at Harvard try to demolish the theory.
The scientists argue that studies on animals since Dr. Hamilton’s day have failed to support it. The scientists write that a close look at the underlying math reveals that Dr. Hamilton’s theory is superfluous. “It’s precisely like an ancient epicycle in the solar system,” said Martin Nowak, a co-author of the paper with Edward O. Wilson and Corina Tarnita. “The world is much simpler without it.”
Other biologists are sharply divided about the paper. Some praise it for challenging a concept that has outlived its usefulness. But others dismiss it as fundamentally wrong.
“Things are just bouncing around right now like a box full of Ping-Pong balls,” said James Hunt, a biologist at North Carolina State University.
Dr. Hamilton, who died in 2000, saw his theory as following logically from what biologists already knew about natural selection. Some individuals have more offspring than others, thanks to the particular versions of genes they carry. But Dr. Hamilton argued that in order to judge the reproductive success of an individual, scientists had to look at the genes it shared with its relatives.
We inherit half of our genetic material from each parent, which means that siblings have, on average, 50 percent [1/2] of the same versions of genes. We share a lower percentage with first cousins [1/8], second cousins [1/32] and so on. If we give enough help to relatives so they can survive and have children, then they can pass on more copies of our own genes. Dr. Hamilton called this new way of tallying reproductive success inclusive fitness.
Each organism faces a trade-off between putting effort into raising its own offspring or helping its relatives. If the benefits of helping a relative outweigh the costs, Dr. Hamilton argued, altruism can evolve.
Dr. Hamilton believed that one of the things his theory could explain was the presence of sterile females among ants, wasps, and some other social insects. These species have peculiar genetics that cause females to be more closely related to their sisters than to their brothers, or even to their own offspring. In these situations, a female ant may be able to spread more genes by helping to raise her queen mother’s eggs than trying to lay eggs of her own.
“Impossible, I thought, this can’t be right. Too simple… By dinnertime, as the train rumbled on into Virginia, I was growing frustrated and angry… And because I modestly thought of myself as the world authority on social insects, I also thought it unlikely that anyone else could explain their origin, certainly not in one clean stroke… By the time we reached Miami, in the early afternoon, I gave up. I was a convert and put myself in Hamilton’s hands. I had undergone what historians of science call a paradigm shift.”
But as the years passed, Dr. Wilson’s enthusiasm for the theory waned. “It was getting tattered,” he said. Many species with sterile females, for example, do not have the strange genetics of ants and wasps. And many species with the right genetics have not produced sterile females. …A number of scientists strongly disagree, though. “This paper, far from showing shortcomings in inclusive fitness theory, shows the shortcomings of the authors,” said Frances Ratnieks of the University of Sussex.
Dr. Ratnieks argues that the Harvard researchers cannot rule out kinship as a driving force in social evolution because their model is flawed. It does not include how closely related animals are.
To see some of the more interesting implications of Hamilton’s theory, see my 2004 VDARE.com article.
Reporting from Juba, Sudan
The man in the orange sunglasses and a fur hat with earflaps seemed more like a jazz musician on a cigarette break than a tribal chief, but as soon as he spoke, village men gathered for a lesson on brides, poor boys and cattle.
The shade was just right. John Modi Jubek crossed his legs, striking as regal a pose as a chief can when he’s sitting in a plastic chair. It was odd to him that a stranger didn’t know the Mundari tribe smiles more upon tall women than on short ones. A father may love his diminutive daughters, but affection does not bring longhorns and riches.
“Tall girls fetch more cattle because their daughters will quickly grow and can be married off to fetch even more cattle,” said the chief, shooing a stubborn fly. “A tall girl can command 60 to 100 cattle from a suitor. A short girl may get 20 head, and, sometimes, short girls overstay their welcome in the father’s home and end up fetching only five cattle. By then, a tall girl has already borne five children.”
The chief paused, letting daughter-cattle ratios sink in. The men shook their heads at his calculations.
The chief was wise, cool in the late morning heat, watching sunflower-high women brush beneath the branches of a big tree with jugs and food sacks balanced on their heads. They strode past a man selling padlocks and Jesus calendars; they glided beyond a short sister wobbling in the sunlight with a numb smile and alcohol on her breath.
“Things get competitive for a tall girl,” said the chief. “Once she reaches 12 years of age, men come to the father and promise many cattle. Of course, a suitor with no cattle will never marry. Our laws forbid that. He is single for life. If he sleeps with someone’s daughter or gets her pregnant, he’ll be killed.”
What do tall women think about marriage and cattle?
The chief bit his lip, bafflement drifting across his face.
“Women have no say,” he said.
Harvard historian Steven Shapin has a long article in the London Review of Books, The Darwin Show, about the apotheosization of Charles Darwin over the last year in service of various contemporary causes, including global warming.
One thing I would add is that the modern cult of beatifying Charles Darwin is dependent upon demonizing his younger half-cousin Francis Galton. Everything politically correct is attributed to Darwin, while everything politically incorrect is attributed to Galton. In reality, Galton was hugely influenced by Darwin, and Darwin, in turn, was influenced by Galton (here’s the lengthy index entry for “Galton, Mr.” from Darwin’s The Descent of Man). Galtonism was seen by both men as the natural evolution of Darwinism.
A featured review, “Charles Darwin, Abolitionist,” by Christopher Benfey, a professor of English, in the Feb. 1, 2009 New York Times Sunday Book Review asserts:
Two arresting new books, timed to coincide with Darwin’s 200th birthday, make the case that his epochal achievement in Victorian England can best be understood in relation to events — involving neither tortoises nor finches — on the other side of the Atlantic. Both books confront the touchy subject of Darwin and race head on; both conclude that Darwin, despite the pernicious spread of “social Darwinism” (the notion, popularized by Herbert Spencer, that human society progresses through the “survival of the fittest”), was no racist.
Adrian Desmond and James Moore published a highly regarded biography of Darwin in 1991. The argument of their new book, “Darwin’s Sacred Cause,” is bluntly stated in its subtitle: “How a Hatred of Slavery Shaped Darwin’s Views on Human Evolution.” They set out to overturn the widespread view that Darwin was a “tough-minded scientist” who unflinchingly followed the trail of empirical research until it led to the stunning and unavoidable theory of evolution. This narrative, they claim, is precisely backward. “Darwin’s starting point,” they write, “was the abolitionist belief in blood kinship, a ‘common descent’ ” of all human beings. …
This is getting American intellectual history confused. The polygenetic theory of human origins tended to appeal to Northern intellectuals, while Southerners didn’t have much time for it since the Old Testament clearly lays out a monogenetic history of humanity going back to Adam and Eve, with the races being descended from Noah’s various sons.
Darwin did spend a number of pages in The Descent of Man considering whether the races were different species before concluding that the different races were, indeed, just different races. If, however, DNA structure co-discoverer James Watson had mentioned in public some of the evidence that Darwin considers on this question, he wouldn’t have been fired. He would have been burned at the stake.
(Here’s my 1999 article from the National Post of Toronto: “Darwin’s Enemies on the Left: Truth v. Equality.”)
It’s all muddled in Benfey’s head because contemporary dogma insists that anyone who believes there are any difference on average between races is in favor of slavery (which then makes stamping out their ideas a moral necessity — If Charles Murray, say, is not exposed to nonstop hatred and lies, the Slave Trade will automatically be re-initiated.)
Even Darwin’s courtship of Emma, whom he winningly called the “most interesting specimen in the whole series of vertebrate animals,” is cleverly interwoven with his developing thoughts on “sexual selection,” the aesthetic preference for certain traits, like skin color in humans or plumage in peacocks, that over time leads to those superficial variations we mistakenly think of as “racial.”
But what if Darwin’s evidence had led to conclusions that did not support his belief in the unitary origins of mankind? Would he have fudged the data? Desmond and Moore don’t really address the question. One is left with the impression that Darwin was amazingly lucky that his benevolent preconceptions turned out to fit the facts.
In his lively and wide-ranging “Angels and Ages,” Adam Gopnik suggests that when facts and values clash we might live in accordance with our beliefs anyway. “It might be true — there is absolutely no such evidence, but it might be true — that different ethnic groups, or sexes, have on average different innate aptitudes for math or science,” he muses. “We might decide to even things out, give some people extra help toward that end, or we might decide just to live with the disparity.” …
Gopnik is as convinced as Desmond and Moore that Darwin was no kind of racist. “The one thing that you could not read into Darwin’s writings was racism,” he writes.
Have any of these people actually read Darwin’s The Descent of Man? If Darwin were alive today, he’d be demonized like James Watson was in 2007. Let’s try a few samples:
There is however no doubt that the various races when carefully compared and measured differ much from each other as in the texture of the hair, the relative proportions of all parts of the body, the capacity of the lungs the form, and capacity of the skull, and even in the convolutions of the brain. But it would be an endless task to specify the numerous points of difference The races differ also in constitution in acclimatisation and in liability to certain diseases Their mental characteristics are likewise very distinct chiefly as it would appear in their emotional but partly in their intellectual faculties Every one who has had the opportunity of comparison must have been struck with the contrast between the taciturn, even morose, aborigines of S. America and the light-hearted talkative negroes. Link
Darwin was an IQ hawk before the invention of the IQ test:
The variability or diversity of the mental faculties in men of the same race, not to mention the greater differences between the men of distinct races, is so notorious that not a word need here be said. Link
The influence of Darwin’s younger half-cousin, the much denounced Sir Francis Galton, coiner of the term “eugenics” and author of the 1869 book Hereditary Genius, on Darwin’s 1871 Descent of Man is evident just from the index of Darwin’s book:
With man, we see similar facts in almost every family, and we now know through the admirable labours of Mr Galton that genius, which implies a wonderfully complex combination of high faculties, tends to be inherited, and on the other hand it is too certain that insanity and deteriorated mental powers likewise run in families… Link
And here’s Darwin sounding like a cross between Galton, Malthus, and Gregory Clark of 2007′s A Farewell to Alms:
We will now look to the intellectual faculties; if in each grade of society the members were divided into two equal bodies the one including the intellectually superior and the other the inferior there can be little doubt that the former would succeed best in all occupations and rear a greater number of children. Even in the lowest walks of life skill and ability must be of some advantage, though in many occupations owing to the great division of labour, a very small one Hence in civilised nations there will be some tendency to an increase both in the number and in the standard of the intellectually able. But I do not wish to assert that this tendency may not be more than counterbalanced in other ways, as by the multiplication of the reckless and improvident, but even to such as these ability must be some advantage. … When in any nation the standard of intellect and the number of intellectual men have increased we may expect from the law of the deviation from an average that prodigies of genius will, as shewn by Mr Galton. appear somewhat more frequently than before Link
Darwin advanced a theory of group selection:
A tribe including many members who, from possessing in a high degree the spirit of patriotism, fidelity, obedience, courage, and sympathy, were always ready to aid one another, and to sacrifice themselves for the common good, would be victorious over most other tribes; and this would be natural selection. At all times throughout the world tribes have supplanted other tribes and as morality is one important element in their success the standard of morality and the number of well endowed men will thus everywhere tend to rise and increase.
Natural Selection as affecting Civilised Nations — I have hitherto only considered the advancement of man from a semi human condition to that of the modern savage But some remarks on the action of natural selection on civilised nations may be worth adding This subject has been ably discussed by … W.K. Greg and previously by Mr Wallace and Mr Galton. Most of my remarks are taken from these three authors. With savages the weak in body or mind are soon eliminated and those that survive commonly exhibit a vigorous state of health We civilised men on the other hand do our utmost to check the process of elimination…
Here’s a particularly amusing part of The Descent of Man:
“Or as Mr Greg puts the case: “The careless squalid unaspiring Irishman multiplies like rabbits; the frugal foreseeing self respecting ambitious Scot, stern in his morality, spiritual in his faith, sagacious, and disciplined in his intelligence, passes his best years in struggle and in celibacy marries late and leaves few behind him. Given a land originally peopled by a thousand Saxons and a thousand Celts, and in a dozen generations five sixths of the population would be Celts but five sixths of the property of the power of the intellect would belong to the one sixth of Saxons that remained. In the eternal struggle for existence, it would be the inferior and less favoured race that had prevailed and prevailed by virtue not of its good qualities but of its faults.” There are however some checks to this downward tendency … Link
And Darwin goes on to lay out some Greg Clark-style caveats, but with no apology to the poor Irish.
And how about this?
“The remarkable success of the English as colonists compared to other European nations has been ascribed to their daring and persistent energy, a result which is well illustrated by comparing the progress of the Canadians of English and French extraction; but who can say how the English gained their energy? There is apparently much truth in the belief that the wonderful progress of the United States as well as the character of the people are the results of natural selection for the more energetic, restless, and courageous men from all parts of Europe have emigrated during the last ten or twelve generations to that great country and have there succeeded best. Looking to the distant future, I do not think that the Rev Mr Zincke takes an exaggerated view when he says: “All other series of events as that which resulted in the culture of mind in Greece and that which resulted in the empire of Rome only appear to have purpose and value when viewed in connection with, or rather as subsidiary to, the great stream of Anglo Saxon emigration to the west.” Obscure as is the problem of the advance of civilisation, we can at least see that a nation which produced during a lengthened period the greatest number of highly intellectual, energetic, brave, patriotic, and benevolent men would generally prevail over less favoured nations.” Link
USA! USA! USA!
On the other hand:
It even appears from what we see — for instance in parts of S. America — that a people which may be called civilised, such as the Spanish settlers, is liable to become indolent and to retrograde when the conditions of life are very easy. Link
Ay carumba …
Here’s the link for “Recent acceleration of adaptive human evolution” by Cochran, Harpending, Hawks, Moyzis, and Wang:
From the LA Times:
By Karen Kaplan, Los Angeles Times Staff Writer
2:44 PM PST, December 10, 2007 The pace of human evolution has been increasing at a stunning rate since our ancestors began spreading through Europe, Asia and Africa 40,000 years ago, quickening to 100 times historic levels after agriculture became widespread, according to a study published today.
By examining more than 3 million variants of DNA in 269 people, researchers identified about 1,800 genes that have been widely adopted in relatively recent times because they offer some evolutionary benefit.
Until recently, anthropologists believed that evolutionary pressures on humans eased after the transition to a more stable agrarian lifestyle. But in the last few years, they realized the opposite was true — diseases swept through societies in which large groups lived in close quarters for a long period.
Altogether, the recent genetic changes account for 7% of the human genome, according to the study published in the Proceedings of the National Academy of Sciences.
The advantage of all but about 100 of these genes remains a mystery, said University of Wisconsin-Madison anthropologist John Hawks …
Most of the genetic changes the researchers identified were found in only one geographic group or another. Races as we know them today didn’t exist until fewer than 20,000 years ago, when genes involved in skin pigmentation emerged, Hawks said. Paler skin allowed people in northern latitudes to absorb more sunlight to make vitamin D.
“As populations expanded into new environments, the pressures faced in those environments would have been different,” said Noah Rosenberg, a human geneticist at the University of Michigan, who wasn’t involved in the study. “So it stands to reason that in different parts of the world, different genes will appear to have experienced natural selection.”
Hawks and his colleagues from UC Irvine, the University of Utah and Santa Clara-based gene chip maker Affymetrix Inc. examined genetic data collected by the International HapMap Consortium, which cataloged single-letter differences among the 3 billion letters of human DNA in people of Nigerian, Japanese, Chinese and European descent.
The researchers looked for long stretches of DNA that were identical in many people, suggesting that a gene was widely adopted and that it spread relatively recently, before random mutations among individuals had a chance to occur.
They found that the more the population grew, the faster human genes evolved. That’s because more people created more opportunities for a beneficial mutation to arise, Hawks said.
In the last 5,000 to 10,000 years, as agriculture was able to support increasingly large societies, the rate of evolutionary change rose to more than 100 times historical levels, the study concluded.
Among the fastest-evolving genes are those related to brain development, but the researchers aren’t sure what made them so desirable, Hawks said.
There are other mysteries too.
“Nobody 10,000 years ago had blue eyes,” Hawks said. “Why is it that blue-eyed people had a 5% advantage in reproducing compared to non-blue-eyed people? I have no idea.” [MORE]
And from The Telegraph in Britain:
By Roger Highfield, Science Editor
Last Updated: 10:01pm GMT 10/12/2007
Good news for future generations of career women: we are evolving to have more children later in life, according to a recent study.
Humankind has evolved more rapidly in the past 5,000 years, at a rate roughly 100 times higher than any other period of human evolution. And an author of the study predicts that this suggests humans will further evolve to have more children later in life. [MORE]
Here’s the abstract and last paragraph of the big paper. (Click the title in blue for the 8 page PDF of the full paper.)
The last paragraph of the discussion:
It is sometimes claimed that the pace of human evolution should have slowed as cultural adaptation supplanted genetic adaptation. The high empirical number of recent adaptive variants would seem sufficient to refute this claim. It is important to note that the peak ages of new selected variants in our data do not reflect the highest intensity of selection, but merely our ability to detect selection. Due to the recent acceleration, many more new adaptive mutations should exist than have yet been ascertained, occurring at a faster and faster rate during historic times. Adaptive alleles with frequencies under 22% should then greatly outnumber those at higher frequencies. To the extent that new adaptive alleles continued to reflect demographic growth, the Neolithic and later periods would have experienced a rate of adaptive evolution more than 100 times higher than characterized most of human evolution. Cultural changes have reduced mortality rates, but variance in reproduction has continued to fuel genetic change. In our view, the rapid cultural evolution during the Late Pleistocene created vastly more opportunities for further genetic change, not fewer, as new avenues emerged for communication, social interactions, and creativity.
Linda Seebach has a column about it:
The old story was that around the time agriculture started to replace hunting and gathering as a way of life for human beings, biological evolution faded into insignificance because it was so much slower. There’s hardly been enough time – only about 10,000 years or so – for human biology to have changed enough so’s you’d notice.
Not so, as studies of the human genome are demonstrating. When people began domesticating animals, planting crops, and living in settled communities, they created environments for themselves quite different from any environments the human species had occupied before, and natural selection proceeded, as it always does, to favor survival and reproductive success for individuals who were, by chance, better adapted to those environments.
The marquee example is retaining the ability to digest milk into adulthood, which is nearly universal among people of European descent, and quite rare elsewhere.
But the shift to agriculture was also important, Cochran said, because agriculture can support a larger population. Any individual might be the next one to draw a winning ticket in the genetic lottery, and the human species was suddenly buying a lot more lottery tickets.
Think of the genes as a crew of thousands of extras, swarming around the sets and the studio lots, auditioning for jobs. They play more than one role, in lots of different movies, for different directors, as circumstances permit.
One day on the set where they’re filming a swords-and-circuses epic, the director spots a spear-carrier who has given an especially elegant performance, impaling a charioteer.
“You there, with the spear? Could you do that again? Yeah?! I’m gonna make you a star!” And – for a quick glimpse into how biology and culture drive each other – if the spear-carrier proves to be bankable, he’ll get more roles, the director will get more movies, the studio will tilt toward making more epics and the extras with good spear-carrying traits will be more likely to succeed in that environment.
Success, in the gene world, is reproductive success – leaving descendants – but given the role of the casting couch in Hollywood, maybe that’s not pushing the metaphor too far.
On the next set over, the director is casting a chick flick. He says to his assistant, “see that looker over there, the one with the purple eyes? Ask her whether she can ride a horse.”
Now the aspiring starlets competing with Elizabeth Taylor for a role in “National Velvet” can take riding lessons. But they can’t do anything to give themselves violet eyes.
The hunter-gatherers competing with pastoralists for food resources could certainly have learned to keep domesticated animals. But if they and their children could not digest milk much past the average age of weaning, it wouldn’t do them any good. In hard times they’d starve while the meek drinkers of milk inherit the earth.
Or at least a broad swath of it from Iceland to South India.
Accelerated biological evolution in humans doesn’t mean that we’re turning into aliens, but there is evidence that hundreds of human genes are under selection pressure, having to do with such things as diet, vitamin metabolism, the functioning of the central nervous system, disease resistance, hair, skin and eye color, the shape of the skeleton and behavioral traits better suited to living in large groups. “We’re tamer,” Cochran said.
I asked him why we’re not developing floppy ears like the silver foxes bred for tameness. [MORE]
Co-author John Hawks is promising an FAQ about it later on Monday evening.
The indefatigable Jason Malloy of GNXP.com offers this summary of initial media reaction:
First wave of media articles:
"Science fiction writers have suggested a future Earth populated by a blend of all races into a common human form. In real life, the reverse seems to be happening.
People are evolving more rapidly than in the distant past, with residents of various continents becoming increasingly different from one another, researchers say."
"Genes have evolved relatively quickly in Africa, Asia and Europebut almost all of the changes have been unique to their corner of the world."
Eureka] Genome study places modern humans in the evolutionary fast lane
"Adds Hawks: "We are more different genetically from people living 5,000 years ago than they were different from Neanderthals.""
"Asked about James Watson's controversial claims that intelligence evolved less effectively in people of African descent, Harpending said the study wasn't designed to test such characteristics. He also cautioned against interpreting the findings as suggesting that people are becoming fundamentally better...
"Evolution is a double-edged sword," he said. "What evolution cares about is that I have more offspring. If you can do it by charming and manipulating, and I'm a hardworking farmer that's going to feed the kids ten years down the road, then you're going to win. Hit-and-run, irresponsible males are reproducing more. That isn't good for anyone except those males, but that's evolution.""
UK] Why the human race is growing apart
"Armand Leroi, Reader in Evolutionary Biology at
Imperial College, , said: "In principle, this could have led to speciation if it had continued, but in practice, it has got to be the case that that cannot happen now. The reason is that this study has looked at largely separated populations in the past, but everything about human history since the industrial revolution weighs overwhelmingly against separation and thus against speciation too. Huge increases in gene flow are going to wipe this trend out."" London
Here’s the press release from the U. of Utah about the big Cochran – Harpending – Hawks – Moyzis – Wang paper. (Look for more coverage tonight and tomorrow in the press.)
Are Humans Evolving Faster?
“We used a new genomic technology to show that humans are evolving rapidly, and that the pace of change has accelerated a lot in the last 40,000 years, especially since the end of the Ice Age roughly 10,000 years ago,” says research team leader Henry Harpending, a distinguished professor of anthropology at the
. Universityof Utah
Harpending says there are provocative implications from the study, published online Monday, Dec. 10 in the journal Proceedings of the National Academy of Sciences:
– “We aren’t the same as people even 1,000 or 2,000 years ago,” he says, which may explain, for example, part of the difference between Viking invaders and their peaceful Swedish descendants. “The dogma has been these are cultural fluctuations, but almost any temperament trait you look at is under strong genetic influence.”
– “Human races are evolving away from each other,” Harpending says. “Genes are evolving fast in Europe, Asia and
Africa, but almost all of these are unique to their continent of origin. We are getting less alike, not merging into a single, mixed humanity.” He says that is happening because humans dispersed from Africato other regions 40,000 years ago, “and there has not been much flow of genes between the regions since then.”
“Our study denies the widely held assumption or belief that modern humans [those who widely adopted advanced tools and art] appeared 40,000 years ago, have not changed since and that we are all pretty much the same. We show that humans are changing relatively rapidly on a scale of centuries to millennia, and that these changes are different in different continental groups.”
The increase in human population from millions to billions in the last 10,000 years accelerated the rate of evolution because “we were in new environments to which we needed to adapt,” Harpending adds. “And with a larger population, more mutations occurred.”
Study co-author Gregory M. Cochran says: “History looks more and more like a science fiction novel in which mutants repeatedly arose and displaced normal humans – sometimes quietly, by surviving starvation and disease better, sometimes as a conquering horde. And we are those mutants.”
Harpending conducted the study with Cochran, a
New Mexicophysicist, self-taught evolutionary biologist and adjunct professor of anthropology at the Universityof Utah; anthropologist John Hawks, a former Utahpostdoctoral researcher now at the Universityof Wisconsin, Madison; geneticist Eric Wang of Affymetrix, Inc. in Santa Clara, Calif.; and biochemist Robert Moyzis of the Universityof California, . Irvine
No Justification for Discrimination
The new study comes from two of the same
Universityof Utahscientists – Harpending and Cochran – who created a stir in 2005 when they published a study arguing that above-average intelligence in Ashkenazi Jews – those of northern European heritage – resulted from natural selection in medieval Europe, where they were pressured into jobs as financiers, traders, managers and tax collectors. Those who were smarter succeeded, grew wealthy and had bigger families to pass on their genes. Yet that intelligence also is linked to genetic diseases such as Tay-Sachs and Gaucher in Jews.
That study and others dealing with genetic differences among humans – whose DNA is more than 99 percent identical – generated fears such research will undermine the principle of human equality and justify racism and discrimination. Other critics question the quality of the science and argue culture plays a bigger role than genetics.
Harpending says genetic differences among different human populations “cannot be used to justify discrimination. Rights in the Constitution aren’t predicated on utter equality. People have rights and should have opportunities whatever their group.”
Analyzing SNPs of Evolutionary Acceleration
The study looked for genetic evidence of natural selection – the evolution of favorable gene mutations – during the past 80,000 years by analyzing DNA from 270 individuals in the International HapMap Project, an effort to identify variations in human genes that cause disease and can serve as targets for new medicines.
The new study looked specifically at genetic variations called “single nucleotide polymorphisms,” or SNPs (pronounced “snips”) which are single-point mutations in chromosomes that are spreading through a significant proportion of the population.
Imagine walking along two chromosomes – the same chromosome from two different people. Chromosomes are made of DNA, a twisting, ladder-like structure in which each rung is made of a “base pair” of amino acids, either G-C or A-T. Harpending says that about every 1,000 base pairs, there will be a difference between the two chromosomes. That is known as a SNP.
Data examined in the study included 3.9 million SNPs from the 270 people in four populations: Han Chinese, Japanese,
Africa‘s Yoruba tribe and northern Europeans, represented largely by data from Utah Mormons, says Harpending.
Over time, chromosomes randomly break and recombine to create new versions or variants of the chromosome. “If a favorable mutation appears, then the number of copies of that chromosome will increase rapidly” in the population because people with the mutation are more likely to survive and reproduce, Harpending says.
“And if it increases rapidly, it becomes common in the population in a short time,” he adds.
The researchers took advantage of that to determine if genes on chromosomes had evolved recently. Humans have 23 pairs of chromosomes, with each parent providing one copy of each of the 23. If the same chromosome from numerous people has a segment with an identical pattern of SNPs, that indicates that segment of the chromosome has not broken up and recombined recently.
That means a gene on that segment of chromosome must have evolved recently and fast; if it had evolved long ago, the chromosome would have broken and recombined.
Harpending and colleagues used a computer to scan the data for chromosome segments that had identical SNP patterns and thus had not broken and recombined, meaning they evolved recently. They also calculated how recently the genes evolved.
A key finding: 7 percent of human genes are undergoing rapid, recent evolution.
The researchers built a case that human evolution has accelerated by comparing genetic data with what the data should look like if human evolution had been constant:
– The study found much more genetic diversity in the SNPs than would be expected if human evolution had remained constant.
– If the rate at which new genes evolve in Africans was extrapolated back to 6 million years ago when humans and chimpanzees diverged, the genetic difference between modern chimps and humans would be 160 times greater than it really is. So the evolution rate of Africans represents a recent speedup in evolution.
– If evolution had been fast and constant for a long time, there should be many recently evolved genes that have spread to everyone. Yet, the study revealed many genes still becoming more frequent in the population, indicating a recent evolutionary speedup.
Next, the researchers examined the history of human populationsize on each continent. They found that mutation patterns seen in the genome data were consistent with the hypothesis that evolution is faster in larger populations.
Evolutionary Change and Human History: Got Milk?
“Rapid population growth has been coupled with vast changes in cultures and ecology, creating new opportunities for adaptation,” the study says. “The past 10,000 years have seen rapid skeletal and dental evolution in human populations, as well as the appearance of many new genetic responses to diet and disease.”
The researchers note that human migrations into new Eurasian environments created selective pressures favoring less skin pigmentation (so more sunlight could be absorbed by skin to make vitamin D), adaptation to cold weather and dietary changes.
Because human population grew from several million at the end of the Ice Age to 6 billion now, more favored new genes have emerged and evolution has speeded up, both globally and among continental groups of people, Harpending says.
“We have to understand genetic change in order to understand history,” he adds.
For example, in
Chinaand most of Africa, few people can digest fresh milk into adulthood. Yet in Swedenand Denmark, the gene that makes the milk-digesting enzyme lactase remains active, so “almost everyone can drink fresh milk,” explaining why dairying is more common in Europe than in the Mediterranean and Africa, Harpending says.
He now is studying if the mutation that allowed lactose tolerance spurred some of history’s great population expansions, including when speakers of Indo-European languages settled all the way from northwest
Indiaand central Asia through Persiaand across Europe4,000 to 5,000 years ago. He suspects milk drinking gave lactose-tolerant Indo-European speakers more energy, allowing them to conquer a large area.
But Harpending believes the speedup in human evolution “is a temporary state of affairs because of our new environments since the dispersal of modern humans 40,000 years ago and especially since the invention of agriculture 12,000 years ago. That changed our diet and changed our social systems. If you suddenly take hunter-gatherers and give them a diet of corn, they frequently get diabetes. We’re still adapting to that. Several new genes we see spreading through the population are involved with helping us prosper with high-carbohydrate diet.”
I’ve been posting teasers for awhile about an upcoming big paper on evolution co-written by the Murderer’s Row of Greg Cochran, Henry Harpending, John Hawks, Bob Moyzis, and Eric Wang. It officially comes out Monday evening, Dec. 10, in the Proceedings of the National Academy of Sciences.
I’m not going to say anymore about it now so that the big boys at the NYT and The Economist can have time to write their stories without anyone jumping the gun … other than to leave you with a Cochran quote as the title of this post.