Esin Deniz/Shutterstock
Human evolution has included numerous hominid species, but few are as iconic as Neanderthals (Homo neanderthalensis). For tens of thousands of years—until roughly 35,000 to 24,000 BCE—Neanderthals and modern humans co‑existed and interbred. Yet the nuances of those unions remain poorly understood.
Today, people of European and Asian descent may carry up to 2 % Neanderthal ancestry. A recent study in Human Genetics uncovers that the genetic imprint came disproportionately from matings between Neanderthal males and modern‑human females.
The team compared genomes from Neanderthal‑free African populations with those of Neanderthal DNA. "We observed a striking imbalance," co‑author Daniel Harris explained. "Modern humans carry no Neanderthal X chromosomes, yet Neanderthal genomes contain 62 % more modern‑human DNA on their X chromosomes than on other chromosomes." This pattern points to a mating preference: Neanderthal males—who transmit a single X chromosome—bred with modern‑human females, who provide two X chromosomes.
Sex chromosomes are inherited asymmetrically. Women contribute two X chromosomes, men only one. Consequently, a child of a Neanderthal father and a modern‑human mother inherits fewer Neanderthal X chromosomes, contributing to the so‑called "Neanderthal desert" on the human X chromosome.
While the genetic evidence is clear, the social dynamics that produced this bias remain speculative. "The prospect that mate preference drove this pattern is compelling," evolutionary biologist Matilda Brindle of Oxford University told National Geographic. "What traits in Neanderthal males captivated modern‑human females—or vice versa—remains an open question."
Although pinpointing the exact motivations behind these unions is challenging, the study leaves one clear inference: if you carry Neanderthal ancestry, at least one of your grandmothers likely mated with a Neanderthal male.
Joe Mcnally/Getty Images
