Friday, June 4, 2010

Neandertal Miscegenation

I like to imagine science as the mind’s eye for the human collective. We became more fully conscious when we realized that Earth is not the center of the universe, that species evolved from shared ancestors, and that human activities alter the atmosphere and climate. Each epiphany, in its own way, disturbed our kind’s self-image. Add to that list the recent discovery that non-African humans are the product of human and Neandertal admixture. In one respect, this underlines what Luigi Luca Cavalli-Sforza called the most important difference in the human gene pool, the genetic Yarlung Zangbo Canyon between Africans and non-Africans. Then again, to discover in their family tree a race once universally considered an inferior species must be lowering the serum testosterone levels of my fellow supra-Saharans. If he were still alive, the politically correct paleontologist, Stephen Jay Gould, would have cause to reconsider the merits of genocide, for he wrote in his 1980 book, The Mismeasure of Man:

"The world might have been ordered differently. Suppose, for example, that one or several species of our ancestral genus Australopithecus had survived—a perfectly reasonable scenario in theory, since new species arise by splitting off from old ones (with ancestors usually surviving, at least for a time), not by the wholesale transformation of ancestors to descendants. We—that is, Homo sapiens—would have faced all the moral dilemmas involved in treating a human species of distinctly inferior mental capacity. What would we have done with them—slavery? extirpation? coexistence? menial labor? reservations? zoos?"

Well, at least we get a choice, right? To be fair, Australopithecus inhabited an entirely different genus. A common definition of species for organisms that reproduce sexually is the group of organisms that would be capable of producing fertile offspring with another member of the group. By that definition, Neandertals are not a separate species. If one categorizes them as a race, they would be a more distant race than any currently in existence, but that distance lends itself to some startling statements, such as a new application of Lewontin’s fallacy, as told by University of Wisconsin—Madison professor John Hawks:

"If you compare humans with other humans today, we differ by about one base pair out of a thousand. So, we’re between ten and twenty times more similar to each other, compared to what we are with chimpanzees. So, if you think about this in terms of years, we think that we divided from chimpanzees—our population split from them something like five-million years ago. Well, that means that humans, on average—two human genes split from each other, in ancestry, something like 500,000 years ago. If you look at us and Neandertals, they’re different from us by just a shade more than we’re different from each other, so that if you compare their genes and our genes, it looks like about maybe 800,000 years is the average. However, that’s recent enough that there are some human genes for which two human copies taken at random are more different from each other than one of them is from the Neandertal."

Hawks is referring to an estimate of the average divergence of autosomal DNA sequences between Neandertals and modern humans of 825,000 years. One should not confuse this with the timing of the populations diverging between 270,000 and 440,000 years ago. The overall genomes of modern humans and Neandertals are 99.84% identical, and only 78 protein-altering DNA changes separate Neandertals from the whole of modern humanity. In the study’s supplement, divergence is calculated not only for Neandertals, but also for a French person, a Han Chinese person, a Papua New Guinean, a Yoruban from West Africa, and a San person from Southern Africa. Here are the autosomal DNA divergence values calculated from a standard ratio of Neandertal-to-human distance over half of the chimpanzee-to-human distance:

French: 8.00
Han: 8.45
Papuan: 9.32
Yoruban: 9.43
San: 10.32
Neandertal: 12.67

This data would seem to suggest a genetic distance spectrum from Europeans to Neandertals with Africans closest to the Neandertals. That is an erroneous conclusion. This data made use of a reference human genome consisting of the DNA of an African-American who is genetically 50% white and 50% African. The numbers are composite autosomal divergences. For the European regions of autosomal DNA, shown below, the values are similar. However, the Neandertal divergence is slightly less, in accordance with the conclusion that Neandertals and non-Africans share 13 regions of DNA or an average of 2% of DNA from mixing.

French: 7.03
Han: 7.69
Papuan: 8.61
Yoruban: 9.27
San: 10.08
Neandertal: 12

The data for the African regions of autosomal DNA, below, look far more confusing. The Yoruban individual was actually not significantly closer to the African regions of DNA than the European regions, and the San person was even slightly (not significantly) closer to the European regions. Africa is the most genetically diverse region of the world. Perhaps its wealth of genetic diversity provided for such a manifestation of Lewontin’s fallacy.

French: 9.28
Han: 9.59
Papuan: 10.14
Yoruban: 9.17
San: 10.19
Neandertal: 13

Part of what makes this revelation so fascinating is its challenge to politically correct notions of race and the out-of-Africa anthropological model. Indeed, Green et al cite an estimate by Wall et al that non-Africans have 14% archaic ancestry. The implication is that the remainder of this archaic ancestry came from some other ancient primate population.

Equally intriguing is how Green et al inadvertently pits a traditional anthropocentrism against taboo, but perhaps commonly held, views of racial supremacy. Now, one should not consider the evidence of intimate relations between Neandertals and the ancestors of non-Africans a comeuppance. Obviously, "neanderthal" became an epithet on par with "cretin" or "jerk." On Razib Khan’s blog, one of the many co-authors of Green et al saw fit to defend Neandertals. "… I see no reason to think that they were not as smart as us."

Suppose the Neandertals were in some meaningful sense an inferior race. At least in a Darwinian sense, leaving a mere 1-to-4% of their genome is an underwhelming legacy. (Actually, Hawks says that each non-African has a different makeup of Neandertal DNA, and Green et al found that when the reference genome European regions were closest to Neandertal DNA, they diverged from the genome of Craig Venter, who is of European descent. Therefore, it is unclear to me exactly what percentage of Neandertal DNA collectively exists today in humans. Plus, Hawks thinks that it is still possible that Africans also have some Neandertal DNA that the study could not detect. That would result in a higher calculation of Neandertal ancestry for both Africans and non-Africans.) Even such a small percentage is a sufficient legacy to discredit the neurotic meme of racial supremacists/nationalists/separatists that impurity is abominable. Many possibilities could explain why so little Neandertal DNA remains in humanity, including natural selection. This leads to one useful argument against the supremacist meme: a Mendelian model.

White supremacists obsess over the dominance of certain phenotypes. Therefore, imagine that a population of brown-eyed individuals completely pair off with a population of blue-eyed individuals, and assume brown eyes are a phenotype with Mendelian complete dominance. There. In a single generation, all blue-eyed people vanish. But don’t cry, because they all passed their DNA onto a generation of brown-eyed heterozygotes. Statistically, about a quarter of the third generation will have blue eyes. Since blue eyes are so superior to brown, the forth generation will consist entirely of the blue-eyed.

Natural selection depends upon context or environment, which leads to a second argument, that of the inevitability of change. Skin color is a perfect example of environmental adaptation. The genes that influence human skin tone appear to be relatively few, and skin-expressed genes comprised the most common genetic differences between modern humans and Neandertals. If white people lost the ability to attain sufficient dietary folic acid, those who live in sunny climates would probably gradually evolve darker, melanin-pigmented skin. Even an otherwise inferior race of Neandertals could have had adaptations to the colder environs that they inhabited. Mixing and millennia may have allowed the non-Africans to absorb such advantages without ultimately losing advantageous African phenotypes.

One counterargument to consider is that holding off on mixing or preserving a differentiating subspecies could allow for further differentiation of some possible value. The process of natural selection is not teleological. Rather, evolution proceeds in whichever direction is immediately advantageous. Genetic separation helps to create a diversity of abilities and biological strategies. Moreover, often evolving in a distant environment leads to adaptations with nearly universal applicability. Just ask the brown tree snake, which immigrated to and now overruns the island of Guam, causing millions of dollars in damages each year. Invasive species cause damages in the United States worth $120 billion annually.

Animal predators as invasive species can devastate an ecosystem. However, a study by Sax and Gaines found that plant invasions of island ecosystems have actually doubled the amount of species diversity. Likewise, when two human populations come in contact, a gradient of mixing can result that creates a more complex form of diversity. Of course, it is hard to argue that leaving tiny segments of their DNA in the human genome was an adequate hedge against extinction for Neandertals. In fact, Harvard geneticist George Church hopes to bring them back from the dead. Nevertheless, the process of evolution did somehow work against these beings. The ethics and logistics of humanity guiding its own evolution receives surprisingly little analysis either from the scientists who might develop new means or from racialists who might possess the will.

With as much impact as humans have on the environment, of course they can shape the forces of evolution, but evolution will never stop. Even with the sprawling health care industry presumably treating hyperlipidemia and hypertension, humans are evolving to have lower cholesterol and systolic blood pressure, according to a recent study by Byars et al. The fact that humans are also evolving to be shorter and fatter may beg the label "dysgenics." However, such oversimplification flies in the face of a study by evolutionary psychologist Satoshi Kanazawa. He found that very liberal individuals have a nearly 12-IQ-point advantage and that atheists have a 6-IQ-point advantage. Monogamous men, but not women, have an IQ advantage, and that says it all. IQ allows one to overcome instinct. Liberal inclinations and abandonment of traditional beliefs can often come with personal costs. Liberals might sacrifice to help unrelated poor people. Atheists might miss opportunities for fellowship. Rather than higher IQ proving the evolutionary superiority of liberals and atheists, these associations may suggest that some height of IQ reduces biological fitness. However expedient blaming the welfare state for the apparent plateau of the Flynn effect in industrialized societies may seem, the context in which high IQ is actually genetically beneficial may be more limited than one might intuit.

The true meaning of the new understanding of Neandertals is that race is simultaneously more real and less important than the previous paradigm led some to believe. Racial purity is neither necessary nor sufficient to preserve the qualities by which some judge races, civilizations, and individuals. Those qualities would include intelligence, peaceableness, functional family values, productivity, and so forth. Nevertheless, race-realism has an important place in modern intellectual thought not only because race is real, but also because leftists have used racial disparities to discount these qualities and to discount the role of genetics in the formation of those qualities. Still, preserving human exceptionalism from fading into the background of natural selection is a cause more extreme and more just than the fancy to preserve any race.