Neanderthal genes present in modern humans might have been integrated into our DNA during a period of interbreeding that began approximately 47,000 years ago and spanned 6,800 years, according to a new study.
Illustrative image from Pixabay
Neanderthals, the extinct close cousins of
Homo sapiens, branched off from our lineage around 500,000 years ago. More than a decade ago, scientists revealed that Neanderthals had interbred with our ancestors who migrated out of Africa. Today, the genomes of modern human populations outside of Africa contain about 1 to 2% Neanderthal DNA.
To pinpoint the timing and location of this interbreeding, researchers analyzed over 300 modern human genomes spanning the last 45,000 years, including samples from 59 individuals dating from 2,200 to 45,000 years ago and 275 present-day modern humans. The findings, published in the
BioRxiv database, suggest a major interbreeding period of 6,800 years starting around 47,000 years ago.
By comparing the levels of Neanderthal DNA across different times and places, the scientists estimated that the majority of this DNA comes from a single major period of interbreeding. The likely encounter between modern humans and Neanderthals is thought to have occurred in Western Asia, a region connecting Africa to Eurasia.
This study also showed that persistent Neanderthal genes were associated with skin color, metabolism, and the immune system, indicating an immediate evolutionary advantage for modern humans facing new pressures outside Africa. By the end of the interbreeding period, approximately 5% of the modern human genome was of Neanderthal origin.
It is possible that subsequent episodes of interbreeding did not leave lasting traces in the current human gene pool. However, the fact that modern human DNA does not appear to be integrated into Neanderthal genomes might suggest lower viability or fertility of hybrids from this direction of interbreeding.