DNA and culture

Cultural differences: A DNA link?
By Nicholas Wade The New York Times
SUNDAY, MARCH 12, 2006
http://www.iht.com/bin/print_ipub.php?file=/articles/2006/03/12/news/genes.php

East Asian and European cultures have long been very different, Richard
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, 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 Pritchard in East Asians have some connection with the
psychological traits described by 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 in Washington, said
"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 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.

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.

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.

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 that thrived 5,000 to 6,000 years ago. They
developed lactose tolerance, the unusual ability to digest lactose in
adulthood. The gene, which shows up in Pritchard's test, is almost
universal among people of Holland and Sweden who live in the region of
the former Funnel Beaker culture.

The most recent example of a society's possible genetic response to its
circumstances is one advanced by 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 collection.

Though this period lasted only from A.D. 900 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.

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 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.

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