Ideas & Trends
The Twists and Turns of History, and of DNA
By NICHOLAS WADE
Published: March 12, 2006
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.
A separate explanation for such long-lasting character traits may be emerging from the human genome. 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. So human nature may have evolved as well.
If so, scientists and historians say, a fresh look at history may be in order. 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.
But like phrenology, a wrong idea that held a basic truth (the brain's functions are indeed localized), the concept of national character could turn out to be not entirely baseless, at least when applied to societies shaped by specific evolutionary pressures.
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.
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.
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."
John McNeill, 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.
There are two aspects to the Cochran theory. The first is the more obvious: when people who have evolved in one place come in contact with people who have evolved somewhere else, genetic differences can have a huge impact on history.
This is particularly blatant in the history of the New World, where a large fraction of the native Indians died soon after 1492 because they hadn't had a chance to adapt to Afro-Eurasian diseases. This allowed whites to conquer the New World easily, and it provided one major impetus for importing disease-resistant Africans as slaves.
You can also see the impact of genetic differences in northern South America and Central America, where you often find Africans living along the hot, feverish coasts, whites living at moderate, pleasant elevations (as in Costa Rica) or along the cool Pacific (as in Peru), and Indians living at extreme altitudes. Bolivian politics, which is much in the news lately, is largely inexplicable unless you understand that whites lose most of their babies to miscarriages at 12,000 feet on the Altiplano, so the high country remains largely Indian almost 500 years after the Conquest.
The second aspect is harder to feel confident about. That's Cochran's contention that even for rooted people whose ancestors have long lived in the same spot, that they have often continued to evolve over time so that they would be genetically different in key regards from their predecessors.
This is certainly possible under the genetic math, but it's hard to develop a lot of confidence in particular examples since it's much harder to observe the lives of dead people and compare them to living people than to contrast two sets of living people.
One promising possibility is the old chestnut question about why the personalities of today's Scandinavians don't seem all that much like their Viking ancestors. It's possible that the aggressive Viking personality was a winning hand in Darwinian terms back in the Dark Ages when other Europeans didn't have adequate defenses against Viking predations. But by the Middle Ages, Europeans had evolved the security system called feudalism and the Vikings were forced to stay home. The most aggressive then tended to slaughter each other in the kind of honor feuds described in Icelandic sagas, while the milder sorts kept their heads down, survived, and multiplied. (On the other hand, I'm rather skeptical of the notion that one group is more or less violent than another group, since humans seem to have a lot of capacity for violence. A nonviolent group probably wouldn't have survived. The obvious differences are in tendencies toward organized and disorganized violence.)
All this is speculation. At present, we don't know what most of the genome does, but eventually we should have a pretty good pictures. It's probably not impossible to to access an adequate sample size of DNA from cemeteries. If so, it's possible that in the second half of the 21st century, history books will read much differently than they do today.