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The molecular record, for all its overwhelming garrulousness, its babel of A’s, C’s, G’s, and T’s, is ambiguous. But the fossilized skulls of our ape lineage seem to tell a clear story, with respect to one trait, anyway. The past few million years have witnessed a steady, plodding increase in the volume of the human lineage’s brains and, presumably, the sophistication of their contents. High intelligence is to great apes as the wing is to birds.
But where are we in that process? Is intelligence still being selected for? Parsimony and uniformitarianism would compel one to answer yes; things in the present are, by and large, as they were in the past. But the way evolution works, whereby mutations arise in one person and slowly spread throughout a population, makes such a question difficult to frame, for if intelligence is still under selection, that could mean that some populations at this very moment are slightly smarter than others — that, perhaps, even certain ethnicities are slightly smarter than others. In the West, speculation on the subject almost automatically tars the speculator as a eugenicist or a racialist.
Bruce Lahn is an evolutionary geneticist and a lab director at the University of Chicago, but he was born and completed the early part of his education in China. A heightened sensitivity to imputations of racialism doesn’t afflict most Chinese, according to Lahn, who, by his own admission, has yet to fully internalize the finer points of Western political correctness. In a pair of 2005 papers, he presented evidence that two genes known to play a role in brain development, microcephalin and ASPM, appear to be undergoing continuing natural selection in historical times. In the penultimate paragraph on microcephalin, he observed that “Sub-Saharan populations generally [have] lower frequencies than others.” And after noting that the ASPM mutation, which he refers to as haplogroup D, is most common in Europeans and Middle Easterners and least common in Sub-Saharan Africans, he speculated, “Although the age of haplogroup D and its geographic distribution across Eurasia roughly coincide with… the development of cities and written language 5,000 to 6,000 years ago around the Middle East, the significance of this correlation is not yet clear.”
It makes sense that some alleles present in Europe, Asia, and the rest of the world wouldn’t appear in Sub-Saharan Africa, and vice versa; population flow has not yet had time to spread all alleles to all parts of the world. However, it’s hard for many of us not to hear in Lahn’s musings on brain genes the ugly implication that Africans are inferior. But such was not Lahn’s intention, nor was that his finding. It was not even what he was investigating.
“Some interpret it as meaning, this is the civilization gene, which is clearly not what we’re trying to say. Maybe we should have said it with more qualifications, to avoid the misconception,” he says. The belief that minor mutations to two genes could bring about a profound and essential difference to an abstract quality as polymorphous as intelligence Lahn sees as springing from America’s confusion about race, its desire to overcome a shameful past, and a fear that old racist beliefs might be given empirical support. Nevertheless, Lahn and his group did ultimately investigate whether possession of the new alleles correlated with intelligence. It did not.
Indeed, possession of Lahn’s variants might have nothing to do with intelligence. “It could impact emotionality, the ability to be patient, for example,” he says. “Our understanding of brain evolution at the phenotype level is so rudimentary right now. We’re very far from actually breaking down the difference between human and other species, let alone among humans.”
Lahn’s result was criticized in subsequent papers, not on ideological grounds, but on technical ones. It was claimed that the signal for selection he thought he’d found was not there. He took the criticism in stride and reanalyzed his data. “We stand by our conclusions,” he says. “We have more unpublished data to support them. We’re convinced that what we published is real.”
Even if Lahn could prove to everyone’s satisfaction that ASPM and microcephalin are under selection, whether intelligence is the trait being selected for would be far from a settled question. It could be, as Lahn suggested, that some other mental trait is being selected, or that the activity of ASPM and microcephalin in other parts of the body is what is under selection. More work will certainly be done. But one can speculate with far more confidence about what drove the dramatic increase in intelligence attested by the fossil record: the advent of human culture.
“Intelligence builds on top of intelligence,” says Lahn. “[Culture] creates a stringent selection regime for enhanced intelligence. This is a positive feedback loop, I would think.” Increasing intelligence increases the complexity of culture, which pressures intelligence levels to rise, which creates a more complex culture, and so on. Culture is not an escape from conditioning environments. It is an environment of a different kind.
Lahn says there could be “some deep-down information theory perspective” that underlies both the rapid increase in human intelligence and an event like the Cambrian explosion, the unequaled diversification of life forms that occurred about 500 million years ago. In an eyeblink, almost every modern body plan came into existence. “It may take a long time to evolve certain components of the body plan, but once you have them, minor tinkering that requires not many changes and very little evolutionary time could give you great diversity in body plans and species,” Lahn says. “The brain may be similar, because it takes a long time to get to a certain level of intelligence, but once you get there, it makes possible a cultural explosion.”
Both events inched toward a threshold that, once crossed, was soon left far behind. The 20th century, in which it took us a mere 60 years to elaborate the horse-drawn carriage into a vehicle that carried us to the Moon, and the howitzer into a 50-megaton nuclear weapon, was another threshold. The forces that we created are on a different scale than those of nature, which works slowly. It seems possible that as our technology grows more subtle, genetic manipulation, gene manufacturing, and even cloning could finally carry us clear of natural selection, but such a commanding position can be maintained only with the survival of a technological society, and that is hardly a foregone conclusion.
The Bleakness of that vision exerts a strong hold on Paul Ehrlich, a professor of population studies at Stanford, who finds in the 20th century a minefield of near misses with extinction. We were saved as often by cunning as by dumb luck: intended to save sleeping families from exploding refrigerators cooled by ammonia, chlorofluorocarbons nearly fried the entire planet. As often as not, some solution creates a new problem.
“The fate of our civilization, and maybe our species,” says Ehrlich, “may be determined by the next five generations. So I don’t really give a shit what’s happening to our genetic evolution.” The global climate is changing too violently for DNA to respond by fiddling around with heat regulation and hair thickness; forests everywhere are being clear-cut too quickly for their inhabitants to adjust, and so food chains are coming undone; the collapse of global fisheries has been identified as an imminent calamity; and a nuclear disaster would constitute a catastrophe many orders of magnitude larger than what nature could readily absorb. If any of these nightmare scenarios comes to pass, Ehrlich fears, evolution will be unable to help us. It may be operating faster than we thought, but it’s not that fast. Problems like smog and acid rain seem almost quaint, and even to be longed for.
Species are transient. There is no question that the day will come when humans are no longer on Earth. But the transience to which we are subject has two faces. The first is extinction. Unlike our forebears, we are aware of how tenuous is our perch atop the food chain. It remains to be seen whether that knowledge has been acquired too late to be of use.
The second face of Homo sapiens’ eventual exit from history is the more hopeful possibility that we may yet evolve into our own successors. Unlike our forebears, we are aware of evolution, which changes our relationship to it, if only by a little, for we are still natural creatures. We continue to evolve, in the face of hunger, disease and a changing ecosystem; but our virtual habitat of culture could enable us to become both subjects of evolution and conscious co-directors of it. “It’s occurring,” says Ehrlich. “There’s no question about it. What’s frightening is the questions we’ll have to ask.”
Science must evolve new tools to raise us to such a commanding vantage, as well as to avert a self-inflicted extinction. Technology might some day enable us to control aspects of evolution, or it may prove to be the ultimate selection regime, culling all of us. Perhaps we already find ourselves wishing we’d lacked the intelligence to monkey with howitzers. Either way, the culture that we’ve created is, strangely, evolution’s most powerful tool and its potential nemesis, the womb of human nature and perhaps its grave. By our own hand: this is how we evolve.
Originally published October 7, 2008
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