Friday, September 26, 2008

Genome indicates polygamy has been the norm

Excerpts from a New Scientist article, Polygamy left its mark on the human genome by Ewen Callaway.

Tens of thousands of years of polygamy has left a mark on our genomes that is a signature that small numbers of males must have mated with lots of females.

Over time, such a pattern will spawn more genetic differences on the X chromosome than other chromosomes. This is because women have two copies of the X, while men only one. In other words, the diversity arises because some men don't get to pass on their genes, while most women do.

"Humans are considered to be mildly polygynous and we descend from primates that are polygynous," says Michael Hammer, a population geneticist at the University of Arizona in Tucson.

Hammer's team discovered more genetic differences in the X chromosome than would be expected if equal numbers of males and females tended to mate, over human history. The only explanation for this pattern is widespread, long-lasting polygyny, he says.

His team's analysis reflects all of human history, and modern monogamy has not even left a blip in our genomes. "I don't know how long monogamy has been with us," Hammer says. "It seems it hasn't been around long, evolutionarily."

Besides, "most societies practice some form of polygamy", he says. Even if most Western men don't take multiple wives, men tend to father children with more females than females do with males, a practice called "effective polygamy".

"It's not unexpected," says Dmitri Petrov, an evolutionary geneticist at Stanford University in California. "Polygany is something you would expect to find." Petrov and his colleagues uncovered the same genetic pattern in fruit flies.

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