NYTimes | Ten thousand years ago, people in southern China began to cultivate rice
and quickly made an all-too-tempting discovery — the cereal could be
fermented into alcoholic liquors. Carousing and drunkenness must have
started to pose a serious threat to survival because a variant gene that
protects against alcohol became almost universal among southern Chinese
and spread throughout the rest of China in the wake of rice
cultivation.
The variant gene rapidly degrades alcohol to a chemical that is not
intoxicating but makes people flush, leaving many people of Asian
descent a legacy of turning red in the face when they drink alcohol.
The spread of the new gene, described in January by Bing Su of the Chinese Academy of Sciences,
is just one instance of recent human evolution and in particular of a
specific population’s changing genetically in response to local
conditions.
Scientists from the Beijing Genomics Institute last month discovered
another striking instance of human genetic change. Among Tibetans, they
found, a set of genes evolved to cope with low oxygen levels as recently as 3,000 years ago. This, if confirmed, would be the most recent known instance of human evolution.
Many have assumed that humans ceased to evolve in the distant past,
perhaps when people first learned to protect themselves against cold,
famine and other harsh agents of natural selection. But in the last few
years, biologists peering into the human genome sequences now available
from around the world have found increasing evidence of natural
selection at work in the last few thousand years, leading many to assume
that human evolution is still in progress.
“I don’t think there is any reason to suppose that the rate has slowed
down or decreased,” says Mark Stoneking, a population geneticist at the
Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
