A Fourth Unknown Early Human Lineage?

A couple of days ago, Nature published a comparison of the genome of a 50,000-year-old Neandertal woman with those of modern humans and Denisovans. The group revealed evidence of interbreeding among at least 4 species of early humans.

Family tree of the four groups of early humans living in Eurasia 50,000 years ago and the gene flow between the groups due to interbreeding. Image credit: Kay Prüfer et al.

Neandertals and Denisovans diverged 300,000 years ago, both of which eventually died out, they left bits of their genetic heritage because they occasionally interbred with modern humans. It is estimated about 1.5 – 2.1% of modern non-African’s can be traced to Neandertals and for Denisovans, only about 6% of Oceanic populations like aborigines, New Guineans, and about 0.2% of Han populations show footprints.

The genome comparisons show that Denisovans interbred with a mysterious, fourth group of early humans also living in Eurasia at the time. That group had split from the others more than a million years ago, and may have been the group of human ancestors known as Homo erectus, which fossils show was living in Europe and Asia at the time.

This current study also indicates that this female Neandertal was highly inbred. She was the daughter of a very closely related mother and father who either were half-siblings who shared the same mother, an uncle and niece or aunt and nephew, a grandparent and grandchild, or double first-cousins. Further analyses suggest that the population sizes of Neandertals and Denisovans were small and that inbreeding may have been more common in Neanderthal groups than in modern populations.


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