STANFORD, CALIFORNIA—Live Science reports that population geneticist Marcus Feldman of Stanford University has proposed a new explanation for the population bottleneck between 5,000 to 7,000 years ago detected in the genes of modern men, which suggest that during this stretch, there was just one male for every 17 females. Feldman and his team conducted 18 simulations that took into account factors such as Y chromosome mutations, competition between groups, and death. The study suggests that warfare among people living in clans made up of males from the same line of descent could have wiped out entire male lineages and decreased the diversity of the Y chromosome. In this scenario, there are not dramatically fewer males, but there was significantly less diversity in their genes. “In that same group, the women could have come from anywhere,” Feldman said. The study found no bottleneck in mitochondrial DNA, which is passed from mother to child. “[The women] would’ve been brought into the group from either the victories that they had over other groups, or they could’ve been females who were residing in that area before,” he said, since the victorious male warriors may have killed all the men they conquered, but kept the women alive and assimilated them. To read about genetic adaptation to life at high elevations, go to “The Heights We Go To.”