Early humans were promiscuous

Turns out that our ancient ancestors weren’t exactly shy when it came to trying new things. A new analysis has revealed that as the ancestors of modern humans (homo sapiens) moved out of Africa and across Eurasia, they would try get it on with just about anyone they came across. In fact, genetic analysis has shown they interbred with at least five different archaic human groups.

A little experimenting never hurt anyone, right?

Three of the archaic groups are unnamed

While two of the archaic groups are currently known – the Neanderthals and their sister group the Denisovans from Asia – the others remain unnamed and have only been detected as traces of DNA surviving in different modern populations.

Denisova cave human evolution
The Denisova cave in the Altai mountains in Siberia where bone fragments of the Denisovan hominid have been found. If the cave is rockin, don’t bother knockin. Credit: MPI for Evolutionary Anthropology

The analysis also found that Island Southeast Asia appears to have been a particular hotbed of diversity.

Researchers from the University of Adelaide’s Australian Centre for Ancient DNA (ACAD) have mapped the location of past “mixing events” (analysed from existing scientific literature) by contrasting the levels of archaic ancestry in the genomes of present-day populations around the world.

“Each of us carry within ourselves the genetic traces of these past mixing events,” says first author João Teixeira. “These archaic groups were widespread and genetically diverse, and they survive in each of us. Their story is an integral part of how we came to be.

“For example, all present-day populations show about 2% of Neanderthal ancestry which means that Neanderthal mixing with the ancestors of modern humans occurred soon after they left Africa, probably around 50,000 to 55,000 years ago somewhere in the Middle East.”

But as the ancestors of modern humans travelled further east they met and mixed with at least four other groups of archaic humans.

Ancestors of modern humans mixed in crowded Island Southeast Asia

Teixeria explains that Island Southeast Asia was already a pretty crowded place before modern humans turned up just before 50,000 years ago.

“At least three other archaic human groups appear to have occupied the area, and the ancestors of modern humans mixed with them before the archaic humans became extinct,” he says.

Archaic human_migration_mixing events
A map showing where the ancestors of modern humans appear to have met and mixed with archaic hominins. Credit: João Teixeir

Using additional information from reconstructed migration routes and fossil vegetation records, the researchers have proposed there was a mixing event in the vicinity of southern Asia between the modern humans and a group they have named “Extinct Hominin 1”.

Other interbreeding occurred with groups in East Asia, in the Philippines, the Sunda shelf (the continental shelf that used to connect Java, Borneo and Sumatra to mainland East Asia), and possibly near Flores in Indonesia, with another group they have named “Extinct Hominin 2”.

“We knew the story out of Africa wasn’t a simple one, but it seems to be far more complex than we have contemplated,” says Teixeira. “The Island Southeast Asia region was clearly occupied by several archaic human groups, probably living in relative isolation from each other for hundreds of thousands of years before the ancestors of modern humans arrived.

“The timing also makes it look like the arrival of modern humans was followed quickly by the demise of the archaic human groups in each area.”

The findings are published in Proceedings of the National Academy of Sciences (PNAS).

This article was first published on Australia’s Science Channel, the original news platform of The Royal Institution of Australia.

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