Magazine article Science News

DNA Diaspora: Humanity May Share Tangled Genetic Roots

Magazine article Science News

DNA Diaspora: Humanity May Share Tangled Genetic Roots

Article excerpt

The scientific debate over the nature of human evolution has taken a new, genetically inspired twist.

Ancient humans migrated out of Africa in at least two major waves, and human groups in Africa, Asia, and Europe have interbred for the past 600,000 years, says geneticist Alan R. Templeton of Washington University in St. Louis.

Templeton's conclusion clashes with the influential theory that modern Homo sapiens originated in Africa around 100,000 years ago and then colonized the rest of the world. In this scenario, humans replaced now-extinct European Neandertals but did not interbreed with them.

"Humans expanded again and again out of Africa, but these expansions resulted in interbreeding, not replacement, and thereby strengthened the genetic ties between human populations throughout the world," Templeton says.

His analysis of geographic patterns in evolutionary trees constructed from DNA in current populations of Africa, Asia, and Europe appears in the March 7 Nature. He reanalyzed previously identified DNA sequences of cells' mitochondria, which are inherited from the mother; of the Y chromosome, which is inherited from the father; and of eight regions of nuclear genetic material, which is inherited from both parents.

Most previous studies have reconstructed human evolution from one gene or one type of DNA. The resulting genetic disparities among populations have been interpreted to support a 100,000-year-old African origin for humanity or, occasionally, to argue for interbreeding among widespread H. sapiens groups over at least the past 1 million years (SN: 2/6/99, p. 88).

Templeton developed a computer program to test whether evolutionary trees, generated from variations in the 10 genetic sequences, exhibit geographic patterns over time. From the patterns that resulted, he calculated whether populations in different regions consistently interbred or had at some point severed their genetic ties. …

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