Evolutionary Psychology and Historical Contingency
AUTHOR: Nicholas Wade
SOURCE: New York Times Magazine
COMMENTARY: Allen MacNeill
I usually like Nicholas Wade's columns, but this one leaves me feeling uncomfortable. Read it, and then we'll talk:
"The Twists and Turns of History, and of DNA"
Let's start with the very first paragraph:
East Asian and European cultures have long been very different, Richard E. Nisbett argued in his recent book "The Geography of Thought." East Asians tend to be more interdependent than the individualists of the West, which he attributed to the social constraints and central control handed down as part of the rice-farming techniques Asians have practiced for thousands of years.
Yes, I know, Ernst Mayr claimed that evolutionary biologists use "population thinking," but sweeping statements about whole groups of people are not generally what evolution is about. The most salient feature of natural populations of individual organisms is the fact that there are significant differences between those individuals. It is precisely such differences that provide the raw material for natural selection. As R. A. Fisher first pointed out, natural selection requires traits that display "continuous variation:" that is, a normal distribution of values for whatever trait is under consideration. For example, if beak size in finches is to undergo natural selection, there must a normal distribution of beak sizes from small to large, with a peak prevalence at some intermediate value.
So where does this leave us? Is "interdependence" the trait being selected for in the article under discussion? If so, I'm extremely skeptical. How would "interdependence" be mediated, at the level of biological processes that could be related to changes in allele frequencies or modifications of developmental pathways? These, after all, are the mechanisms that must be modified for biological evolution to occur, and especially if a biological adaptation is to evolve via natural selection.
True, the article does go on to suggest that there is empirical evidence that selection is happening:
Humans have continued to evolve throughout prehistory and perhaps to the present day, according to a new analysis of the genome reported last week by Jonathan Pritchard, a population geneticist at the University of Chicago.
Fine, so far: what Pritchard & Co. have found are segments of DNA (i.e. "genes") whose frequencies in different populations have changed in ways that are consistent with what one would expect as the result of natural selection. But then comes the punchline:
So human nature may have evolved as well.
It's like that famous Sidney Harris cartoon: "And then a miracle happens..." The logical step from changes in allele frequencies in the human genome to changes in "human nature" is one for which no empirical evidence is presented, and for which such evidence may be impossible to obtain.
Why is this important? Wade goes on to note:
Evolutionary changes in the genome could help explain cultural traits that last over many generations as societies adapted to different local pressures. Trying to explain cultural traits is, of course, a sensitive issue. The descriptions of national character common in the works of 19th-century historians were based on little more than prejudice. Together with unfounded notions of racial superiority they lent support to disastrous policies.
What disasterous policies? Well, those of the Nazis during World War II, for starters. Ascribing "general characteristics" to "societies" is precisely what the Nazis did. Jews as a group were venal, grasping, self-interested, conniving, dishonest, etc. etc. No matter that individual Jews might express such traits to varying degrees; what mattered in Nazi racial policy was the "biological" traits of whole groups of people.
Wade gives a nod to this caveat:
...the concept of national character could turn out to be not entirely baseless, at least when applied to societies shaped by specific evolutionary pressures.
Indeed. Is there any biological sense in calling "national character" an adaptation? Even the question seems laughable, and the answer is, of course, no. Evolutionary biologists can't actually agree on what constitutes an adaptation; if they could, no one would have read nor given any credence to Lewontin and Gould's famous "spandrels" paper. Evolutionary biologists with a proven track record, like Lynn Margulis (of "serial endosymbiosis" fame) have railed against the "pan-adaptationism" of most evolutionary biologists. Furthermore, the work of Jukes, Kimura, Ohta, and others have shown that the vast majority of DNA (and many of the proteins for which it codes) have evolved via "neutral" mechanisms that produce nothing like adaptations in the classical sense.
So, is there anything to this report beyond the recapitulation of long-ago discredited social prejudice? Let's see:
In a study of East Asians, Europeans and Africans, Dr. Pritchard and his colleagues found 700 regions of the genome where genes appear to have been reshaped by natural selection in recent times. In East Asians, the average date of these selection events is 6,600 years ago. Many of the reshaped genes are involved in taste, smell or digestion, suggesting that East Asians experienced some wrenching change in diet. Since the genetic changes occurred around the time that rice farming took hold, they may mark people's adaptation to a historical event, the beginning of the Neolithic revolution as societies switched from wild to cultivated foods.
In other words, the frequencies of certain regions of the genome have changed out of synch with other regions. The inference, therefore, is that the altered regions (e.g. "genes") have changed in frequency as the result of natural selection. So far, I have no problem with this. But look at what these genes/regions code for: physiological processes, virtually all of them mediated by enzymes or regulatory proteins of some kind (i.e. taste, smell, digestion, etc.) No problem: genes do, indeed, code for proteins, and therefore there is nothing particularly controversial about inferring that the non-conserved regions identified by Pritchard & Co. have evolved as the result of selection for altered diet, etc.
But can one then extrapolate from resultsand inferences like these to "national character?" Consider:
Some of the genes are active in the brain and, although their role is not known, may have affected behavior. So perhaps the brain gene changes seen by Dr. Pritchard in East Asians have some connection with the psychological traits described by Dr. Nisbett.
Now hold one, here: how do you get from changes in allele frequencies to changes in behavior? E. O. Wilson cautioned that we can't do this until the architecture of the brain can be broken down and its relationship to behavior studied in detail. Are we at that point? Hardly; cognitive psychologists can't even agree on how "thoughts" are related to behavior. Wade states this uncertainty clearly: "...their role is not known..." Exactly.
So can we make confident statements about changes in alleles being related to changes in "national character?" I don't think so, but clearly other folk do:
Some geneticists believe the variations they are seeing in the human genome are so recent that they may help explain historical processes. "Since it looks like there has been significant evolutionary change over historical time, we're going to have to rewrite every history book ever written," said Gregory Cochran, a population geneticist at the University of Utah. "The distribution of genes influencing relevant psychological traits must have been different in Rome than it is today," he added. "The past is not just another country but an entirely different kind of people."
Yeah, but do you rewrite the history books before or after you've shown the actual connections between the alleles and the relevent behaviors? And even when you do this (assuming you can), do you then extrapolate from that to "national character?" Not unless you believe that individual variations in "character" amount to virtually nothing.
But natural selection acts primarily at the level of individuals, or so the overwhelming majority of evolutionary biologists from Charles Darwin to G. C. Williams have asserted. Yes, Hamilton's "kin selection" seems to displace the focus of selection from individuals to their shared alleles, but in the real world it is still individual organisms that live and die, reproduce or fail to, and therefore remain the ultimate locus of action of natural selection.
But the article suggests that these recent findings might provide a kind of Seldonian theory of "psychohistory" by means of which we could understand and even predict the behavior of human groups (a la Isaac Asimov's Foundation series). In science fiction, that's fine, but we're talking about science here. The problem with historical processes is that they are stubbornly resistant to mathematicization. You can't formulate an equation that describes (much less predicts) something like the fall of the Roman Empire or the invention of gunpowder. In an earlier posting to this list, I pointed out that historical contingency is the root of the problem of macroevolutionary theory, in that historical events by definition can't be described nor predicted by mathematical models.
Isn't that exactly the unstated assumption what underlies statements like these? Seems so to me:
John McNeill [no relation, BTW], a historian at Georgetown University, said that "it should be no surprise to anyone that human nature is not a constant" and that selective pressures have probably been stronger in the last 10,000 years than at any other epoch in human evolution. Genetic information could therefore have a lot to contribute, although only a minority of historians might make use of it, he said.
The only way in which "genetic information" could contribute to an understanding of human history would be if:
1) there is a one-to-one correlation between genes and human behaviors,
2) there is a one-to-one correlation between sets of genes and "national characters",
3) individual differences within "societies" are swamped by the "national character" of such societies, and
4) the contingency that seems to affect historical processes can be shown to be entirely reducible to the foregoing.
Does anyone anywhere suggest that we are even remotely close to demonstrating any of these conditions? If so, I want to know where such results have been peer-reviewed and published. All I've seen so far is a lot of airy hypothesis spinning.
But wait, it gets weirder:
The political scientist Francis Fukuyama has distinguished between high-trust and low-trust societies, arguing that trust is a basis for prosperity. Since his 1995 book on the subject, researchers have found that oxytocin, a chemical active in the brain, increases the level of trust, at least in psychological experiments. Oxytocin levels are known to be under genetic control in other mammals like voles. It is easy to imagine that in societies where trust pays off, generation after generation, the more trusting individuals would have more progeny and the oxytocin-promoting genes would become more common in the population. If conditions should then change, and the society be engulfed by strife and civil warfare for generations, oxytocin levels might fall as the paranoid produced more progeny.
Notice that key phrase: It's easy to imagine... Indeed it is. Doing real science is hard work. So far, I don't see any evidence of it having been done, here. True, some people have done a lot of field work on human behavior:
Napoleon Chagnon for many decades studied the Yanomamo, a warlike people who live in the forests of Brazil and Venezuela. He found that men who had killed in battle had three times as many children as those who had not. Since personality is heritable, this would be a mechanism for Yanomamo nature to evolve and become fiercer than usual.
But Chagnon's work shows quite explicitly that the patterns of behavior he has described can be explained by natural selection at the level of individuals. That's precisely what Chagnon's point was about unokais (the men who had killed other men in battle): their reproductive success could be directly linked to their behavior in a way that supported the concept of individual selection. That is, most individual Yanomami men are "fierce" because they are the offspring of individual men who were "fierce." "Fierceness," therefore, is a trait of individual Yanomami men, and only secondarily (and by analogy) of Yanomamo society.
All of the foregoing seems to me to be arguing that "societies" have "genomes," and that changes in those genomes can be directly linked to changes in those societies. In the following quote, a tendency to confuse the "genomes" of individuals and groups becomes glaringly obvious, at least to me:
Since the agricultural revolution, humans have to a large extent created their own environment. But that does not mean the genome has ceased to evolve. The genome can respond to cultural practices as well as to any other kind of change. Northern Europeans, for instance, are known to have responded genetically to the drinking of cow's milk, a practice that began in the Funnel Beaker Culture which thrived 6,000 to 5,000 years ago. They developed lactose tolerance, the unusual ability to digest lactose in adulthood. The gene, which shows up in Dr. Pritchard's test, is almost universal among people of Holland and Sweden who live in the region of the former Funnel Beaker culture.
But societies can't have genomes; only individuals do. There is a distressing tendency these days to equate the genome of individuals with the elements that are shared between individuals in "societies" (i.e. reproductively panmictic populations). When people make this equation, they are in effect reinventing Platonic idealism in its most pernicious form. The "national character" becomes the "ideal form" which is coded for by the "genome" of the society, and along the way all individual differences (the raw material upon which all selection depends) are brushed aside.
And finally, of course, the Jews are explicitly mentioned:
The most recent example of a society's possible genetic response to its circumstances is one advanced by Dr. Cochran and Henry Harpending, an anthropologist at the University of Utah. In an article last year they argued that the unusual pattern of genetic diseases found among Ashkenazi Jews (those of Central and Eastern Europe) was a response to the demands for increased intelligence imposed when Jews were largely confined to the intellectually demanding professions of money lending and tax farming. Though this period lasted only from 900 A.D. to about 1700, it was long enough, the two scientists argue, for natural selection to favor any variant gene that enhanced cognitive ability.
One theme in their argument is that the variant genes perform related roles, which is unlikely to happen by chance since mutations hit the genome randomly. A set of related mutations is often the mark of an evolutionary quick fix against some sudden threat, like malaria. But the variant genes common among the Ashkenazi do not protect against any known disease. In the Cochran and Harpending thesis, the genes were a response to the demanding social niche into which Ashkenazi Jews were forced and the nimbleness required to be useful to their unpredictable hosts.
And then comes the kicker:
No one has yet tested the Cochran-Harpending thesis, which remains just an interesting though well worked out conjecture. But one of its predictions is that the same genes should be targets of selection in any other population where there is a demand for greater cognitive skills. That demand might have well have arisen among the first settled societies where people had to deal with the quite novel concepts of surpluses, property, value and quantification. And indeed Dr. Pritchard's team detected strong selection among East Asians in the region of the gene that causes Gaucher's disease, one of the variant genes common among Ashkenazim.
That is, all we have here is a correlation between alleles, traits at the level of individuals, and a suggested correlation with "societal" traits. But as every good scientist knows, correlation is not proof of causation. On the contrary, valid arguments for causation always rely on analysis of mechanisms, and here the foregoing studies are completely mute. There are no actual mechanisms by which the correlations can be shown to have worked. Indeed, how exactly would one test the "Cochran-Harpending thesis" other than to collect more data supporting the suggested correlation?
I call myself an evolutionary psychologist, and must admit that I have suggested hypotheses such as those described in this article. But, when I have done so, I have tried to be careful to emphasize that what I have been doing is suggesting a hypothesis, not validating a theory. It may be that E. O. Wilson is correct and that we may have to wait until we can show the connections between alleles, neural circuitry, behaviors, and social patterns. If so, I'd rather wait than have our theories co-opted by yet another totalitarian regime bent on the "improvement" of our "national character."
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Published: March 12, 2006