Mammoths maketh man 21/4/04. By the Wellcome Trust Sanger Institute Did northeast Asian populations eat well 30 000 years ago?

New research shows that northern and southern populations in East Asia followed dramatically different fates around 30 000 years ago. The growth of the northern populations might have occurred simply because they could hunt and eat mammoths: an abundant source of nutrition.

The research, by an international team led by Dr Chris Tyler-Smith from the Wellcome Trust Sanger Institute, was published in the journal Genetics.

This genealogy on a grand scale used Y chromosome sequences to look at 27 populations in China, Mongolia, the Koreas and Japan. The populations in the northern areas expanded between 34 000 and 22 000 years ago, before the last Ice Age (around 20 000 years ago). The southern populations expanded only after 18 000-12 000 years ago.

"Although previous studies have looked at population changes averaged over large areas, this is the first analysis that has the resolution to look at local changes," said Dr Tyler-Smith. "The differences are dramatic and speak of very dissimilar conditions in the regions north and south of the Yangtze (Changjiang) River."

"When we first saw them, we thought our calculations must be wrong" said Yali Xue, also at the Wellcome Trust Sanger Institute. "But the differences would not go away. The genetic record clearly told us there were two different stories for the peoples of this region."

To study human populations, researchers analyse the frequencies of DNA sequence variations. The Y chromosome is especially useful because it is inherited only through the male line and therefore analysis is simpler. A long-established or a large population will tend to have more variation; a young population, or one derived from a relatively small set of 'founders', will have less.

Two types of Y-chromosome marker are used to study male lineages in human populations. One, binary markers, looks at base differences in Y-chromosome sequence, but can be biased because they are based on pre-selected DNA markers from known populations. The second, short tandem repeats (STRs) or microsatellites, is essentially free of this bias because STRs are variable in all populations.

In this study, Tyler-Smith and colleagues found greatest levels of variation of Y-chromosome sequence in the populations from the north of the region, around modern Mongolia and northern China. This contrast between north and south was consistent for all groups studied and suggested all northern groups started to expand before the last Ice Age, whereas all southern groups started to expand after it.

While the extreme north of Asia was inhospitable to humans, Siberia supported an abundance of large mammals - most notable, to modern eyes, the mammoth. By contrast, the southern regions did not support significant numbers of large mammals and the population expanded only after the Ice Age - perhaps as the populations used plant products, such as tubers on a significant scale.

"We asked ourselves what differentiated these two groups," continued Dr Tyler-Smith. "What was different about the environment in the north? The most appealing explanation is the vast abundance of the 'mammoth steppe' - a time and a region when large numbers of grazing animals and their predators roamed the grassy plains."

"At that time, the southern regions of East Asia were probably densely forested and impenetrable to humans. The only robust explanation for the early success of the northern populations is that they enjoyed a better and richer diet: they thrived on mammoths and other large animals."

Adapted from a news release by the Wellcome Trust Sanger Institute .

Further reading

Xue Y, et al. Male demography in East Asia: a north-south contrast in human population expansion times. Genetics. 2006 Apr;172(4):2431-9. Epub 2006 Feb 19. Abstract