Mingling key to modern man

By Robert Lee Hotz
National Correspondent

March 7, 2002

Spreading out of Africa like starlings, early humans conquered the world by embracing the strangers they encountered around the globe, not by forcing them into extinction, as many researchers thought, according to a new analysis of human genetic history.

In the textbook view, the founding fathers of modern humanity emerged suddenly from Africa about 100,000 years ago and swept into oblivion all other prehuman species -- Neanderthals, for example -- that they encountered.

A new and elaborate computer genealogy of 11 inherited traits compiled by Alan Templeton at Washington University in St. Louis today will present a very different slant on the origins of diversity.

Templeton's work, being published today in Nature, suggests that "interbreeding, not replacement," was the rule for successive waves of primitive humans migrating out of Africa. By mingling, these ancestral human groups "strengthened the genetic ties between human populations throughout the world," said Templeton, who studies the history and geography of genes.

In his view, the ancient world was a vast melting pot in which tribes of human ancestors scattered, rejoined and scattered again. As they did so, they intermingled inherited traits across thousands of generations to mix the palette of modern humanity.

Templeton's work is the latest riposte in a 20-year-long debate in which anthropologists, archeologists, molecular biologists and population geneticists have battled over human origins with rounds of research papers scattered like hand grenades.

Several specialists in the field enthusiastically hailed the new study of evolutionary parentage as "brilliant," while others briskly dismissed it as "hocus-pocus" and "nonsense."

For all their differences, both camps agree that the earliest ancestors of humankind evolved in Africa about 2 million years ago.

Where the scientists part company is in deciding how those ancestral groups gave rise to anatomically modern people -- with their small pointed jaws, smooth foreheads, high rounded skulls and advanced mental abilities.

Frustrated by the ambiguous fossil record, researchers have turned to the genes that code for growth and development to flesh out this missing chapter of human evolutionary history.

To reach his conclusions, Templeton combined published data on 11 parts of the human genome. He analyzed mitochondrial DNA -- genetic material that each person inherits directly from his or her mother -- as well as data from genes carried on the Y chromosome, which is inherited only from fathers. He also looked at genes on other chromosomes that can be inherited from either parent.

His computer analysis detected considerable gene mixing and evidence of two separate waves of migration out of Africa into Asia and Europe -- the first between 420,000 and 840,000 years ago and a more recent one between 80,000 and 150,000 years ago.

Robert Lee Hotz writes for the Los Angeles Times, a Tribune Co. newspaper.

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