Modern humans evolved a 'selfish' X chromosome after Africa exodus

Around 50,000 years ago, a new X chromosome appears to have been introduced into modern humans that had not long left Africa.

There was probably exceptionally strong selection for parts of this chromosome because, today, most people of less-recent African ancestry have inherited those regions.

Kasper Munch Terkelsen at Aarhus University in Denmark, who led the research, thinks these regions may contain bits of so-called selfish DNA that promote their work.