WHY THE HUMAN RACE IS GROWING APART
KarabakhOpen
>From The Times
12-12-2007 12:07:32
Races have evolved away from each other over the past 10,000 years,
according to new research that challenges standard ideas about the
biological significance of ethnicity.
A genetic analysis of human evolution has shown that rather
than slowing to a standstill it has speeded up, with different
pressures on different populations pushing racial groups further
apart. Scientists behind the findings suggest that European, African
and Asian populations grew genetically more distinct from each other
over several thousand years, as their environments took them down
different evolutionary paths.
This would call into question the popular scientific view that race
has little or no biological meaning, as the genetic similarities
between ethnic groups greatly outweigh differences.
While this remains true – all humans share more than 99 per cent of
their DNA – the new work indicates that variations tend to differ
between races, and that these became more, not less, pronounced.
"Human races are evolving away from each other," said Henry Harpending,
Professor of Anthropology at the University of Utah, who led the study.
"Genes are evolving fast in Europe, Asia and Africa, but almost all
of these are unique to their continent of origin. We are getting less
alike, not merging into a single, mixed humanity.
"Our study denies the widely held assumption that modern humans
appeared 40,000 years ago, have not changed since and that we are
all pretty much the same. We aren’t the same as people even 1,000 or
2,000 years ago."
The research is published in the journal Proceedings of the National
Academy of Sciences. If the trend towards increasing genetic diversity
were to continue, it could lead ultimately to the development of
different species.
Most scientists, however, think this is now highly unlikely.
The research identified evolutionary currents only in past times. In
the modern era, greater movement and gene flow between the continents
has probably slowed or even reversed patterns of increasing genetic
difference, making the evolution of separate human species virtually
impossible.
Armand Leroi, Reader in Evolutionary Biology at Imperial College,
London, said: "In principle, this could have led to speciation
if it had continued. In practice, it has got to be the case that
that cannot happen now. The reason is that this study has looked
at largely separated populations in the past, but everything about
human history since the Industrial Revolution weighs overwhelmingly
against separation and thus against speciation too. Huge increases
in gene flow are going to wipe this trend out."
The study shows that over the past 5,000 years, new genetic variants
have been emerging at a rate 100 times faster than in any other period
of human evolution.
If this rate were to have remained the same since humans and
chimpanzees diverged around six million years ago, the genetic
difference between the two species would be 160 times greater than
it is.
The scientists said this reflected the great increase in human
populations over that period, which has allowed more beneficial
mutations to emerge.
Changes in the human environment, particularly the rise of agriculture,
also created new selective pressure to which humans adapted.
Tribes and traits
— The research compared genetic information from four modern ethnic
groups – Japanese, Han Chinese, Yoruba Nigerians and Utah Mormons of
northern European ancestry
— Examples of traits that differ among the groups include the lactase
gene, which allows people to digest milk into adulthood
— Most Europeans have this gene but it is absent in most Africans
and Asians. This may reflect the ancestral importance of dairy farming
in Europe
— Disease-resistance genes also differ. About 10 per cent of Europeans
have CCR5, which confers some resistance to HIV, and which may have
evolved to give resistance to smallpox
— Previous research by Professor Harpending has suggested that the
above-average intelligence found among Ashkenazi Jews could be the
result of selection in medieval Europe, where they tended to work in
trade and finance. This, however, has been criticised by scientists.