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Friday, March 06, 2009

Are Humans Still Evolving?

This is a follow-up to my earlier posting about the latest issue of Discover magazine [Ascent of Darwinism]. I want to discuss another article in that issue: "Are We Still Evolving" by Kathleen McAuliffe. The title of the web version is: They Don't Make Homo Sapiens Like They Used To.

In a minute we'll look at the quality of science journalism in this article, but first a little background.

The point of the article is that human evolution may have accelerated enormously in the past 40,000 years. The idea is based almost entirely on a few papers by John Hawks and his colleagues. What they did was to look at various polymorphisms in the human genome. The most common variants are single nucleotide mutations (single nucleotide polymorphism = SNP = "Snips"). Some people will have one tpe of variant while other people will have another. Almost all of these variants are neutral—they have no visible or functional effect—but some of them will affect fitness.

Some SNPs can linked to variants (alleles) that are under selection. If you assay for enough SNPs, you'll find several that just happen to be located near variants that are being selected. If selection is rapid then the nearby SNPs will be swept up along with the actual variant that improves fitness. A block of SNPs that forms a cluster found in many individuals is called a "haplotype." The presence of these haplotypes is evidence of a selective sweep (rapid increase in frequency due to selection).

As time goes on these clusters are broken up by recombination so using this technique you only see examples of recent adaptations.

Hawks and his colleagues claim to have found more than 11,000 examples of genes that are being selected in the human population. (Humans have about 20,000 genes.) They conclude that human evolution has accelerated in the past 40,000 years because our hunter-gatherer ancestors settled down to become farmers and this created a new environment. We have been adapting to that new environment ever since.

The important paper is Hawks et al. (2007). For more information read: Is Evolution Linked to Environmental Change?, Accelerated Human Evolution, Are Humans Evolving Faster? and Human Evolution Has Accelerated

The work is controversial. Many people are skeptical of both the result and the explanation. The general consensus among evolutionary biologists is "wait and see." They treat this as a preliminary result because they are well aware of the technical problems and how easy it is to score false positives. The technology is not foolproof.

Evolutionary biologists are not surprised by the claim that humans are evolving. The textbooks are full of examples of recent human evolution by both natural selection and random genetic drift. Besides, the evidence is all around us—you only have to look at the different appearance of people in Africa, Asia, and Europe to see the obvious. We also have the well-studied examples of human migration out of Africa and of coalescence to identify Mitochondria Eve. This is more evidence of recent human evolution.

So, evolutionary biologists aren't the least bit surprised by evidence of human evolution but they're skeptical of this particular study because it claims recent accelerated human evolution. The paper isn't that exciting to most people who know about evolution.

The popular press had a fit, aided and abetted by the PR departments at several universities and, more recently, by a newly published book: The 10,000 Year Explosion: How Civilization Accelerated Human Evolution.

This brings us to the article in Discover. The author, Kathleen McAuliffe, is a freelance writer who specializes in science and medicine. She has an M.A. in natural science. She just won an Alicia Patterson Journalism Fellowship "to continue her research into human evolution from the Stone Age to the present."

Here's how the article begins ....
For decades the consensus view—among the public as well as the world’s preeminent biologists—has been that human evolution is over. Since modern Homo sapiens emerged 50,000 years ago, “natural selection has almost become irrelevant” to us, the influential Harvard paleontologist Stephen Jay Gould proclaimed. “There have been no biological changes. Everything we’ve called culture and civilization we’ve built with the same body and brain.” This view has become so entrenched that it is practically doctrine. Even the founders of evolutionary psychology, Leda Cosmides and John Tooby, signed on to the notion that our brains were mostly sculpted during the long period when we were hunter-gatherers and have changed little since. “Our modern skulls house a Stone Age mind,” they wrote in a background piece on the Center for Evolutionary Psychology at the University of California at Santa Barbara.
I think this is wrong. I do not believe that the consensus among the world's preeminent evolutionary biologists1 is that human evolution is over.

I'm not familiar with the Gould quotation. It seems to have been uncovered by Cochran and Harpending, two of the authors on the Hawks et al. paper. They use it on the first page of their book The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. Even if it's accurate, it does not represent the mainstream view of most evolutionary biologists.
So to suggest that humans have undergone an evolutionary makeover from Stone Age times to the present is nothing short of blasphemous. Yet a team of researchers has done just that. They find an abundance of recent adaptive mutations etched in the human genome; even more shocking, these mutations seem to be piling up faster and ever faster, like an avalanche. Over the past 10,000 years, their data show, human evolution has occurred a hundred times more quickly than in any other period in our species’ history.
There are two things wrong with this. First, the hype about blasphemy is a serious distortion of the truth. The scientific literature is full of examples of recent human evolution. Haven't you heard of the sickle cell gene, lactose intolerance, and blood types?

Second, while the Hawks et al. paper is interesting, it is extremely misleading to imply that their evidence is unchallenged. That's not good science journalism. (Incidentally, the peer-reviewed paper says that human evolution accelerated in the past 40,000 years, not 10,000.)

It's not until you get to the sixth paragraph that you find any sort of balance.
Not surprisingly, the new findings have raised hackles. Some scientists are alarmed by claims of ethnic differences in temperament and intelligence, fearing that they will inflame racial sensitivities. Other researchers point to limitations in the data. Yet even skeptics now admit that some human traits, at least, are evolving rapidly, challenging yesterday’s hallowed beliefs.
What kind of balance is that? Where's the sober description of the consensus view; namely, that humans are always evolving and the evidence of Hawks and his colleagues isn't convincing?

John Hawks is featured prominently in this article.
These overriding trends are similar in many parts of the world, but other changes, especially over the past 10,000 years, are distinct to specific ethnic groups. “These variations are well known to forensic anthropologists,” Hawks says as he points them out: In Europeans, the cheekbones slant backward, the eye sockets are shaped like aviator glasses, and the nose bridge is high. Asians have cheekbones facing more forward, very round orbits, and a very low nose bridge. Australians have thicker skulls and the biggest teeth, on average, of any population today. “It beats me how leading biologists could look at the fossil record and conclude that human evolution came to a standstill 50,000 years ago,” Hawks says.
Beats me how John could possibly think that "leading biologists" have ignored the data.

McAuliffe also interviews Henry Harpending and Robert Moyzis, two other authors on the original paper. Not surprisingly, she gets a similar story from them about how their revolutionary ideas are overthrowing entrenched dogma.

McKauliffe is now on a role and she includes a number of just-so stories.
Paralleling the constant war against pathogens, human sperm may also be evolving at high speed, driven by the race to get to the egg before another man’s sperm. “It could be that cities create more sexual partners, which means fiercer competition among males,” Hawks says. Because sperm can fertilize an egg up to 24 hours after being ejaculated in the vagina, a woman who copulates with two or more partners in close succession is setting up the very conditions that pit one man’s sperm against another’s. Hawks infers that “sperm today is very different from sperm even 5,000 years ago.” Newly selected mutations in genes controlling sperm production show up in every ethnic group he and his team have studied; those genes may affect characteristics including abundance, motility, and viability. The selection for “super sperm,” Hawks says, provides further corroboration that our species is not particularly monogamous—a view widely shared by other anthropologists.
As agriculture became established and started creating a reliable food supply, Hawks says, more men and women would have begun living into their forties and beyond—jump-starting the selection pressure for increased life span. In support of that claim, Moyzis is currently performing a genetic analysis of men and women in their nineties who are of European ancestry. He has traced many early-onset forms of cancer, heart disease, and Alzheimer’s to older human gene variants. “The idea is that people with more modern variants tend to have greater resistance to these chronic illnesses of old age and should be overrepresented in the age 90-plus population,” Moyzis says.
Harpending and Cochran had previously—and controversially—marshaled similar evidence to explain why Ashkenazi Jews (those of northern European descent) are overrepresented among world chess masters, Nobel laureates, and those who score above 140 on IQ tests. In a 2005 article in the Journal of Biosocial Science, the scientists attributed Ashkenazis’ intellectual distinction to a religious and cultural environment that blocked them from working as farm laborers in central and northern Europe for almost a millennium, starting around A.D. 800. As a result, these Jews took jobs as moneylenders and financial administrators of estates. To make a profit, Harpending says, “they had to be good at evaluating properties and market risks, all the while dodging persecution.” Those who prospered in these mentally demanding and hostile environments, the researchers posit, would have left behind the most offspring.
The last one is accompanied by a passing reference to reality, "Critics note that the association between wealth and intelligence in this interpretation is circumstantial, however."

Six pages into the article we come to this ...
Despite all these clues that human evolution has continued and accelerated into modern times, many evolutionary biologists remain deeply skeptical of the claims. Their resistance comes from several directions.

Some independent experts caution that the tools for studying the human genome remain in their infancy, and reliably detecting genomic regions that have been actively selected is a challenging problem. The hypothesis that human evolution is accelerating “all rests on being able to identify recent areas of the genome under natural selection fairly accurately,” says human geneticist Jonathan Pritchard of the University of Chicago. And that, he warns, is tricky, involving many different assumptions (about population sizes on different continents, for instance) in the poorly documented period before recorded history.

Given such uncertainties, researchers are more likely to be persuaded that a mutation has been recently selected if they understand its function and if its rise in prevalence meshes well with known human migratory routes. Genetic variants fitting that description include those coding for lighter skin coloring, resistance to diseases such as malaria, and metabolic changes related to the digestion of novel foods. There is broad consensus that these represent genuine examples of recent adaptations.
Hmmm ... there is "broad consensus" that humans have evolved recently.

How is that consistent with the outrageous claims in the opening paragraphs?

Do we blame science writer Kathleen McAuliffe or John Hawks and his colleagues for this misleading article?

Does the article contribute positively to educating the general public about human evolution or would we be better off if it had never been published?

1. I realize that McAuliffe said "biologist," not "evolutionary biologists" but surely the only biologists who count are the experts in the field? After all, you wouldn't ask ecologists their opinion about biochemistry, would you?

Hawks, J., Wang, J.T., Cochran, G., Harpending, H.C. and Moyzis, R.K. (2007) Recent acceleration of human adaptive evolution. Proc. Natl. Acad. Sci. (USA) 104:20753-20758 [doi: 10.1073/pnas.0707650104]

[Photo Credit: MSNBC]


John S. Wilkins said...

Not two weeks ago a geneticist, Steve Jones, gave a talk at my hood in which he claimed exactly what Hawks says - that evolution stopped with the arrival of culture 50,000 years ago.

Larry Moran said...

I've blogged about the strange views of Steve Jones: Steve Jones Says Human Evolution Is Over and Have Humans Stopped Evolving?.

He's not alone, but that does not mean that he and his misguided friends define the consensus among evolutionary biologists.

Allen MacNeill said...

I agree that both evolutionary biology as a whole and Hawks' research to be specific are somewhat misrepresented in the article. However, I completely and vehemently disagree with the idea that "we would be better off if the article (and, by implication, others like it) had never appeared."

On the contrary, what the author of the article seems to be primarily guilty of is exaggeration, rather than serious errors of either fact or interpretation. But exaggeration is precisely what both sells magazines and entices most non-scientists to read about science. As a child I was inspired to become an evolutionary biologist by reading the immensely popular books by Roy Chapman Andrews. I have met many other evolutionary biologists (and especially paleontologists) who were similarly inspired by Andrews. Yet he was certainly guilty of the same kind of exaggeration as the author of the article cited in this blog post.

The problem, of course, is that to make most scientific research interesting to non-scientists it must be "tarted up", and the people best trained to do this are science journalists. If a non-scientist is sufficiently motivated by reading something like the article criticized here to read the original research reports, or even more so to become a scientist, then the hyperbole perpetrated by the science journalist would have been worth it.

If, on the other hand, most non-scientists were only to read the highly technical research reports that appear in peer-reviewed journals (which are difficult to find outside of most university libraries anyway), they would find them to be both technically opaque and horrendously badly written.

So I, for one, can only applaud the efforts of most science journalists, and those scientists like Carl Sagan and Richard Dawkins, who actually work hard to make science as interesting to non-scientists as it is to those of us who actually do science for a living.

Anonymous said...

Allen MacNeill writes: But exaggeration is precisely what both sells magazines and entices most non-scientists to read about science.

I wonder what the sales figures for "Natural History" magazine were before, during and after the period when Gould was writing his non-exaggerated scientific essays for them? Those essays certainly enticed this non-scientist to read more about evolutionary biology.

Re the stuff about Jews and non-farming occupations: While the history is generally correct, why would evolution be necessary to explain any of the observed effects? Numbers of Nobelists or chess grandmasters, if Jews are indeed over-represented among them, can easily be explained by a cultural tradition that turned to education as the way to success. (I'm leaving the IQ tests alone, believing scores on such tests are evidence of little other than the ability to score on such tests.)

Anonymous said...

Numbers of Nobelists or chess grandmasters, if Jews are indeed over-represented among them

Indeed they are. Hugely.

can easily be explained by a cultural tradition that turned to education as the way to success.

Every time I hear the cultural explanation, I ask myself: What is culture? Is it entirely independent on genes? And I feel that this is a chicken and egg question. E.g., there is such a thing as "prison culture" which in many ways remarkably similar across various countries/ethnicities.
Do we explain it all by the selective pressures of penicentiary regime or is it indeed reasonable to assume that the kind of people who are there (on average, of course) bring their genes to built a new culture? (And obviously, it's a combination of nature/nurture again). Once you allow the possibility that the prison culture has something - anything - to do with genes, there is no way back. Logically, one then has to allow a possibility that "culture" in general is itself a combination of genes, environment and pure chance. Having allowed that, there is nothing intrinsically wrong with bringing the genes as part of the explanation of any observed cultural differences. And it is quite clear that culture can exert a strong positive feedback on the development of populations (e.g., some wrote elaborate stories 2000 years ago and others don't count to three to this day).

UNRR said...

This post has been linked for the HOT5 Daily 3/7/2009, at The Unreligious Right

Anonymous said...

DK: Your prison culture argument is a poor one. If one selects similar personality traits from within a few larger societies and isolates them under similar conditions then obviously they will develop sub-cultures that share various similarities. So what? It does not prove that the distribution of personality traits is different between the different cultures (rather the opposite if anything) and it certainly has nothing to say about the genetic basis of personality or culture.

While one may accept that genes influence differences in personality between individuals and that culture is an emergent property of many personalities that is still a long way from demonstrating that genetic differences are the primary, significant, or even a detectable source of differences between cultures. The whole notion is ridiculous. It completely ignores the effects of historical contingency and the environment which certainly do play a major role, not to mention the effects of different frequencies of Toxoplasma infection (which is at least as plausible a factor as the one that you cite). You have not established that genes affecting personality traits are unevenly distributed amongst cultures or that the differences in frequencies are large enough to have an effect. Even if you did manage to find a correlation, it would say nothing about the direction of causation. After all, I can't think of a good reason why culture couldn't exert selective pressure that would change allele frequencies, a reversal of the causal order that you advocate.

Larry Moran said...

Allen MacNeill writes,

On the contrary, what the author of the article seems to be primarily guilty of is exaggeration, rather than serious errors of either fact or interpretation. But exaggeration is precisely what both sells magazines and entices most non-scientists to read about science.

There's a fierce battle going on over many of the claims by anthropologists. Why not write an article about that conflict, giving examples from both sides?

No need to exaggerate. No need to take sides. The public will be informed about real science and how it works.

And they will be better off.

Anonymous said...

Here's the Gould quote you were unfamiliar with:

Gould, SJ. 2000. "The Spice of Life: An Interview with Stephen Jay Gould"

Larry Moran said...

Anonymous says,

Here's the Gould quote you were unfamiliar with:

Thank-you for the link. The quote is accurate. It was a remarkably stupid thing for Gould to have said.

In previous comments on this topic, Gould has been careful to distinguish between human evolution, per se, and evolution of the brain. He claimed that most changes in human society are cultural and not because our brains have improved in the past 40,000 years.

For example, he wrote in The Mismeasure of Man (p. 354),

Human societies change by cultural evolution, not as a result of biological alteration. We have no evidence for biological change in brain size or structure since Homo sapiens appeared in the fossil record some fifty thousand years ago. (Broca was right in stating that the cranial capacity of Cro Magnon skulls was equal if not superior to our.) [my emphasis]

Biological (Darwinian) evolution continues in our species, but its rate, compared with cultural evolution, is so incomparably slow that its impact upon the history of Homo sapiens has been small.

Anonymous said...

I've blogged about the strange views of Steve Jones: Steve Jones Says Human Evolution Is Over and Have Humans Stopped Evolving?.

He's not alone, but that does not mean that he and his misguided friends define the consensus among evolutionary biologists.

Yeah, where do Jones and his misguided fellow travelers (regardless of who they are, or how innumerable they may be) get off by appearing to define the consensus among evolutionary biologists? To hear Moran tell it, that task is incredibly nuanced, and, to judge by the examples he cites, so beset with contradictory assertions and ideologically-driven, facially idiotic equivocations that only someone as exquisitely sensitive and learned as Moran himself is qualified to divine whether or not any such consensus might exist (what any such a consensus might be - if it were to exist - is an even more rarefied matter). And if you dare to suggest that the issue might be susceptible to a numbers-based answer, it just confirms that you are an insensitive, unscientific lout.

Like his ideological leader Gould and others of that political ilk, it seems that Moran will reluctantly acknowledge that evolution (or, as he appears to prefer, "positive natural selection" (the pragmatic distinction between them eludes me as the end result seems to be the same)), has occurred "recently", but will insist that any such changes are of little real significance. Certainly there CANNOT EVER have been any changes that would have resulted in any important differences between the brains of various "racial" groups (and of course "race" must be put in quotes because "races" don't really exist, inasmuch as ideologically driven egalitarians can be found in every population group) (albeit in differing proportions - aye, there's the rub)!

I wonder if any Cardinal tried to claim that there was no Catholic consensus regarding heliocentrism? I doubt that any would have had the chutzpah. And I doubt that there was any need for Galileo to list all the evidence of such a consensus - it was as obvious as the sun in the sky.

Anonymous said...

To Mack:

Before you rant against Larry's positions, perhaps you can first learn what they are. Your distortions are ridiculous.

It should be totally obvious that Prof Moran would never ever equate evolution and "positive natural selection". Also, he fully acknowledges that "races" do exist and regularly mocks people who claim otherwise.

Anonymous said...

I read the article in Discover and it seems that there is balance in the article. Admittedly the 'NOT SO FAST' section comes quite near the end of the article but that just makes for a more exciting read. However, I can see why somethings in the article might be a bit annoying to someone who knows a lot about evolutionary biology (particularly the Hawks quote about leading biologists coming to the conclusion that human evolution came to a standstill 50,000 years ago).

Anonymous said...

All you people are idiots if you don't think evolution is happening!

Anonymous said...

kym werth is cool

Anonymous said...

go emma stephonson

Anonymous said...

Steve Jones makes absolutely no sense. He says that evolution isn't happening, but yet he says that mutations are still occurring in a lot of males over the age of 35! so it is obvious that Steve Jones is an idiot.

Anonymous said...

KYM WERTH loves honors american studies. And believes that evolution is still happening in todays society. But she thinks that humans are evolving faster than mice because they eat more... This also causes obesity; she recently predicted.