SUNDAY NEW YORK TIMES
March 12, 2006

Ideas & Trends

The Twists and Turns of History, and of DNA

By NICHOLAS WADE

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.

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.

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 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.

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.

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.