2021-research-reinforced-that-mating-across-groups-drove-human-evolution

Evidence that cross-continental Stone Age networking events powered human evolution ramped up in 2021.

A long-standing argument that Homo sapiens originated in East Africa before moving elsewhere and replacing Eurasian Homo species such as Neandertals has come under increasing fire over the last decade. Research this year supported an alternative scenario in which H. sapiens evolved across vast geographic expanses, first within Africa and later outside it.

The process would have worked as follows: Many Homo groups lived during a period known as the Middle Pleistocene, about 789,000 to 130,000 years ago, and were too closely related to have been distinct species. These groups would have occasionally mated with each other while traveling through Africa, Asia and Europe. A variety of skeletal variations on a human theme emerged among far-flung communities. Human anatomy and DNA today include remnants of that complex networking legacy, proponents of this scenario say.

It’s not clear precisely how often or when during this period groups may have mixed and mingled. But in this framework, no clear genetic or physical dividing line separated Middle Pleistocene folks usually classed as H. sapiens from Neandertals, Denisovans and other ancient Homo populations.

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“Middle Pleistocene Homo groups were humans,” says paleoanthropologist John Hawks of the University of Wisconsin–Madison. “Today’s humans are a remix of those ancient ancestors.”

New fossil evidence in line with that idea came from Israel. Braincase pieces and a lower jaw containing a molar tooth unearthed at a site called Nesher Ramla date to between about 140,000 and 120,000 years ago. These finds’ features suggest that a previously unknown Eurasian Homo population lived at the site (SN Online: 6/24/21), a team led by paleoanthropologist Israel Hershkovitz of Tel Aviv University reported. The fossils were found with stone tools that look like those fashioned around the same time by Middle Easterners typically classified as H. sapiens, suggesting that the two groups culturally mingled and possibly mated.

Interactions like these may have facilitated enough mating among mobile Homo populations to prevent Nesher Ramla inhabitants and other Eurasian groups from evolving into separate species, Hershkovitz proposed.

But another report provided a reminder that opinions still vary about whether Middle Pleistocene Homo evolution featured related populations that all belonged to the same species or distinct species. Researchers studying the unusual mix of features of a roughly 146,000-year-old Chinese skull dubbed it a new species, Homo longi (SN Online: 6/25/21). After reviewing that claim, however, another investigator grouped the skull, nicknamed Dragon Man, with several other Middle Pleistocene Homo fossils from northern China.

If so, Dragon Man — like Nesher Ramla Homo — may hail from one of many closely related Homo lines that occasionally mated with each other as some groups moved through Asia, Africa and Europe. From this perspective, Middle Pleistocene Homo groups evolved unique traits during periods of isolation and shared features as a result of crossing paths and mating.

a photo of Chinese Homo skulls

So even after the Middle Pleistocene, networking among ancient Homo groups may have helped make us who we are today.

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