Thursday, April 29, 2010

Cheap shots and collateral damage

Ségolène Royal and supporters

A University of New Mexico research team has announced that the human gene pool seems to have admixture from an outside source, most likely from the Neanderthals and other archaic humans. This conclusion was based on analysis of variation in microsatellite DNA from European, Asian, and Oceanic populations. Since microsatellite DNA is thought to be of neutral selective value, any variation must be due to the slow gradual accumulation of new mutations or admixture from outside our gene pool.

The researchers pinpointed two admixture events:

Using projected rates of genetic mutation and data from the fossil record, the researchers suggest that the interbreeding happened about 60,000 years ago in the eastern Mediterranean and, more recently, about 45,000 years ago in eastern Asia. (Dalton, 2010)

This analysis suffers from several problems. For one thing, it is based on rough estimates, i.e., the length of time that modern humans have existed outside Africa and the speed at which new mutations accumulate in microsatellite DNA. There is also the dubious assumption that this DNA is never affected by natural selection.

Nonetheless, this announcement has delighted anthropologists like John Hawks, Greg Cochran, and Alan Templeton who have long argued against the ‘Out of Africa’ model of human origins. As multiregionalists, they used to argue that modern humans evolved out of earlier archaic populations in Africa, Europe, and Asia. Thus, modern Europeans would primarily be descended from Neanderthals, Modern Asians from Peking man, and so on.

Today, the multiregional model is no longer accepted, and its proponents are now backing a compromise. Modern Europeans, for instance, would largely descend from the wave of humans that spread out of Africa 60,000 to 40,000 years ago, but they would still have some admixture from Neanderthals in their gene pool.

Will this debate ever be settled? Yes, and very soon. That’s the good news. In a few months, the reconstruction of the Neanderthal genome will be published. By comparing it with the genome of modern Europeans, we should find out whether any genes flowed from one to the other. Preliminary comparisons have already been done and to date have found … nothing.

Now the bad news. The triumph of the ‘Out of Africa’ model will be heavily politicized. Although I support this model, I feel nothing but shame for the cheap shots that many other adherents have made. A common one has been to cast multiregionalists as ‘racists.’

This name-calling appears in a New York Times article that presents multiregionalists as “inheritors of a culturally infected biology” and its opponents as “supporting our better inclinations.” In an interview, paleontologist Chris Stringer clearly enjoyed being on the side of the angels, while snidely accusing the other side of racism. He recalled an encounter with Carleton Coon in a Harvard washroom where the aged professor referred to one of his critics as ''that . . . Jew Weiner.''

What irks me about this anecdote is not that it is unverifiable (washroom conversations are not published and Coon has long been dead), but simply its irrelevance. Suppose it could be shown that Carleton Coon had regularly sodomized his grad students. Or would microwave live kittens. Or had bad breath. What would that prove or disprove about the multiregional model? Nothing. This is ad hominem at its sleaziest.

In the same interview, Stringer went on to say that our species is so young that differences among humans can only be skin-deep:

Since so little time has passed since they [modern humans] decamped from Africa, dispersing to the far regions of the world -- 100,000 years being a mere paleontological moment -- ''only slight differences, if any, in intellect and innate behavior are likely to have evolved between modern human populations.'' We are ''all Africans under our skin.''

Uh, 100,000 years is not a mere paleontological moment. A population can undergo significant physical and genetic change in as little as eight generations. In fact, many animal species go back only to the last ice age (25,000-10,000 BP). Evolutionary change is due primarily to the intensity of natural selection and only secondarily to the passage of time. Indeed, the faster such change has occurred, the more important it must be, since it is being driven by intense natural selection and not by adaptively neutral processes like genetic drift or founder effects.

I can forgive journalists for not knowing the above. I find it harder to forgive Chris Stringer, who is fully aware of how fast natural selection can operate. There is no point in winning a debate if you inflict a lot of collateral damage in the process.

Clearly, there has been collateral damage. The catch phrase “We are all Africans” has taken on a life of its own, with almost 100,000 Google hits. In the last French election, Ségolène Royal cited the latest findings in paleontology when she proclaimed, “Nous sommes tous des Africains!” This cute expression is even appearing in high school textbooks.

And we’ll probably see it in newspaper headlines when the Neanderthal genome is finally published.

References

Dalton, R. (2010). Neanderthals may have interbred with humans. Genetic data points to ancient liaisons between species. Naturenews, April 20.
http://www.nature.com/news/2010/100420/full/news.2010.194.html

Hawks, J. (2010). Multiregional evolution lives! John Hawks Weblog, April 21
http://johnhawks.net/weblog/reviews/evolution/introgression/joyce-dalton-interbreeding-2010.html

Richards, R.J. (1997). Neanderthals need not apply, New York Times, August 17, 1997.
http://www.nytimes.com/books/97/08/17/reviews/970817.17richart.html

9 comments:

ben10 said...

Let's see how fast he gets a grant.

gcochran said...

Want to bet?

THE_TRUTH said...

I've been rereading several articles on epigenetics and generative dynamics by Mae-Wan Ho, Saunders, Gottlieb, Gilbert, and Waddingron with a particular interest in Lamarckian epigenesis, and what may be foolish suppression of areas of evolutionary development and selection, which, in my opinion, provide much additional dirt on the story of how modern humans became us. Really, is the real difference between modern Humans and Neanderthals found in all that junk DNA (and its many languages), rather than 3 billion base letters.

When it comes to the idea that the entire modern human genome has been completely sequenced and that the same will be true of the Neanderthal genome, I really have to laugh. With non-coding genes occupying possibly 98% of the human genome, I really question how gene-environment-culture interactions relate to similarity between the modern human and the Neanderthal genome, and in particular, how culture, and executive functions, did nothing but create a slowed (and at times robust) change to brain morphology and body plan modification.

Basically why is it that an exact copy of the modern human genome, for the Neanderthals, a prerequisite, if they as a species, are to classified as a direct ancestor of us ? 100K, 60K and 35K years is an enormous period of time, for small changes to occur, in any species genome, and most certainly, as seen in Kangaroos, dogs, cats and whales, races (different races within species) can still breed and produce reproductively viable offspring. I mean, why would Homo sapiens and Neanderthals be any different. Does anyone really believe that our ancestors and Neanderthals only jumped into bed twice over a 100K year period.

Mark said...

Does it really matter? If they showed tomorrow that we are twenty percent Neanderthal, people would just point to it as evidence that mixing is as old as humanity itself.

Anonymous said...

It would seem obvious that both existing African populations and populations out of Africa have been diverging from the ancestral population.

So, while we are all "Africans" our genetic distance from modern Africans might be larger than from the ancestral Africans we are all descended from.

Fred Scrooby said...

What North Americans think of as "Africans" are West-Central African Negroes. I recall reading an article saying those didn't exist until 14K years ago when some West-Central African pygmies turned into them under pressures stemming from the advent of farming along the headwaters of the Niger River or something like that. So, whatever "Africans" came out of Africa's extreme northeastern tip 40 or 60 or 80 or 100 K years ago weren't Negroes, who (please correct me) didn't exist until tens of thousands of years later.

Tod said...

When Cro-Magnons were discovered (in France) French scientists realized they were the basis for all human progress and therefore the (German) Neanderthal valley was the home to a bestial dead end species. Some Germans probably referred to Marcellin Boule as 'that Frenchman'.

No doubt there was tendentious opposition to Coon given the implications of his argument, was he expecting a pat on the back from certain quarters? The cheap shot against Coon would be that his idea of parallel or converging evolution producing the appearance of a human species was silly. His far fetched hypothesis discredited all biologic anthropology. Stringer is just talking in the moral argot which everyone in his line of work has to phrase their ideas - or lack of them - in to be considered acceptable nowadays.

Peter Frost said...

Everyone,

There may have been some intermixture between modern humans and Neanderthals, enough perhaps to produce significantly mixed local populations here and there. But such populations were probably marginalized and pushed to extinction, just as the Neanderthals had been.

So far the evidence is very weak for any surviving admixture. If we look at mtDNA, the Neanderthals are no closer to modern Europeans than they are to modern Asians or modern Africans.

Again, this debate will come to a close when the Neanderthal genome is finally released. But I'm not expecting any big surprises.

I agree that Coon's model was silly, but its silliness could have been exposed without resorting to ad hominem attacks. Such attacks debase the currency of debate.

Fred Scrooby said...

”I recall reading an article saying [West-Central African Negroes] didn't exist until 14K years ago” ( -- my comment above)

I just looked it up -- turns out the place where I read the article was here, at this blog:

http://evoandproud.blogspot.com/2008/02/origins-of-black-africans.html .

”I'm not expecting any big surprises.” ( -- Peter Frost)

Steve Sailer appears to feel differently:

http://isteve.blogspot.com/2010/05/neanderthal-within.html .