Most Men's Family Lines Vanished About 5,000 Years Ago
Women's lines survived, and the lopsided pattern points to rival groups killing men and keeping women.
Modern Wisdom · How War Shaped Human Evolution - David Geary - #1172About 5,000 to 7,000 years ago, most men's family lines vanished while women's lines carried on.
Genetic data point to about 17 women who left continuing lines for every one man, says David Geary, who studies how war shaped human evolution. The clue is in the Y chromosome, passed from father to son, which suddenly shows far less variety in that period.
His explanation is organized violence by groups of related men. Armed with weapons and moving outward with early farming, one kin group could kill the men in another group and erase that group's Y line. The women were often kept.
Disease or famine does not fit as well, because those would have reduced women's lines too. A crash concentrated almost entirely in men points to other men doing the killing.
Questions people ask
How can DNA show this thousands of years later?
Men pass a Y chromosome to their sons, while both sexes pass on other DNA and mothers pass on mitochondrial DNA. Researchers compare the variety in those lines over time, and around 5,000 to 7,000 years ago the male lines narrow sharply while female lines stay much broader.
Does the 17-to-1 ratio mean there were 17 times more women alive?
No. It means that among people living then, far fewer men than women ended up with descendants whose lines persist today. Many men were alive, but their sons did not survive or reproduce in a continuing line.
Who was doing the killing?
The source points to expanding groups of related men, armed and organized, moving into new territory after agriculture emerged. In later examples such as pastoralist expansions into Europe, incoming men displaced local men while having children with local women.