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Why the human race is growing apart

 
 
 
 
 
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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.

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