Women on the Move

[Martha_05]

Women on the Move
Make way, Magellan: women were the
true global explorers (genetically speaking).

When Virginia Woolf wrote, "As a woman, my country is the whole world," she was speaking out against nationalism but her words, it now appears, were very close to scientific truth. History has always depicted women as habitues of home and hearth, with men the intrepid explorers of the globe. A new genetic study suggests that, overall, the exact opposite is true: women have, over time, traveled far further afield than men.

Population geneticist Mark Seielstad of the Harvard School of Public Health reached this conclusion after studying DNA sequences (distinctive genetic patterns) that descend exclusively through either the male or female line. One set of sequences resides on the Y chromosome, the sex chromosome that only men inherit; the other is contained within mitochondrial DNA, or mtDNA, which is passed on to children only by their mothers. (Mitochondria, the energy- producing units within cells, carry their own, independent genes. A human egg is stuffed with over 100,000 mitochondria while a sperm brings none into the egg, so a child inherits his or her mitochondrial DNA exclusively from the mother.)

Seielstad teamed up with L. Luca Cavalli-Sforza and Eric Minch at the Stanford University School of Medicine to examine the distributions of genetic sequences among men and women around the world. The researchers looked at 62 mtDNA sequences in two populations each from Europe, West Asia, Israel, Asia, and North America, and at 32 Y chromosome sequences in 54 populations in Africa, Oceania, Asia, Europe and the Americas. These sequences occur in a number of different variants.

Women's genes appeared very well mixed all around the world, suggesting a great deal of movement from place to place; men's genes told a very different story. On average, every population contained 80 to 85 percent of all the possible mtDNA variants. "The populations seemed very similar, one to another, when you looked at mitochondrial DNA," says Seielstad. "Exactly the opposite was true for the Y chromosome." Only 35 percent of all the possible variants for the Y chromosome sequences studied could be found in every population. These results appear in the November, 1998 issue of Nature Genetics.

The efficient scattering of women's genes is probably a result of a custom called patrilocality, which has been practiced over the centuries by some 70 percent of traditional agricultural societies. "This institution prescribes that the wife should move into the household of her husband, who's often living with his parents," Seielstad says. "When that got started it's hard to say, but certainly by the time agriculture was invented land began to be inherited through the male line, which fixed men to particular pieces of property. And as women move five or ten kilometers among different villages, it translates into an overwhelming effect. It's like a chain that generation by generation might move a very short distance, but if you multiply that by ten thousand years it's quite a large distance."

The famous male explorers of history--Scott of the Antarctic, Marco Polo, Magellan and the like--covered a lot of ground, but the slow, steady migration of women is what really matters in the gene pool. "Men do in many societies travel greater distances over their lifetimes--they go on expeditions and so on--but they generally return to their natal household," Seielstad notes. "And any kind of reproduction that goes on while they're away from home is probably fairly insignificant."

--by Josie Glausiusz
Posted 1/28/99
Discover Magazine

[Daybelys]

thank you for sharing this with us cappy

[goloso]

but it's all beginning to make sense...........

[kingnica10]

gracias