According to a new study published in the journal Cell, modern Papuans carry hundreds of gene variants from two Denisovan lineages — distinct from Altai Denisovans — that separated over 350,000 years ago; one of those lineages is so different from the other that they really should be considered as an entirely new species of archaic hominin.
Denisovans were probably dark-skinned, unlike the pale Neandertals. The picture shows a Neanderthal man. Image credit: Mauro Cutrona.
“People used to think that Denisovans lived on the Asian mainland and far to the north,” said study senior author Dr. Murray Cox, a researcher in the School of Fundamental Sciences at Massey University, New Zealand.
“Our work instead shows that the center of archaic diversity was not in Europe or the frozen north, but instead in tropical Asia.”
It had already been clear that Island Southeast Asia and New Guinea was a special place, with individuals there carrying more archaic hominin DNA than anywhere else on Earth.
The region also was recognized as key to the early evolution of Homo sapiens outside Africa.
But there were gaps in the story.
Genome sequences from Island Southeast Asia suggest two independent Denisovan lineages, distinct from the Altai Denisovan, that have contributed to modern Papuan genomes, with one group potentially present east of the Wallace Line and thus capable of crossing geographical barriers. Image credit: Jacobs et al, doi: 10.1016/j.cell.2019.02.035.
To help fill those gaps, Dr. Cox and colleagues excavated archaic haplotypes from 161 genomes spanning 14 island groups in Island Southeast Asia and New Guinea.
Their analyses uncovered large stretches of DNA that didn’t jibe with a single introgression of genes from Denisovans into humans in the region. Instead, modern Papuans carry gene variants from two deeply divergent Denisovan lineages.
In fact, the team estimates that those two groups of Denisovans had been separated from one another for 350,000 years.
“Taken together with previous work — which has pointed to a third Denisovan lineage in the genomes of modern Siberians, Native Americans, and East Asians — the evidence suggests that modern humans interbred with multiple Denisovan populations, which were geographically isolated from each other over deep evolutionary time,” the researchers said.
“Our findings show that modern humans making their way out of Africa for the first time were entering a new world that looked entirely different from the one we see today.”
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Guy S. Jacobs et al. Multiple Deeply Divergent Denisovan Ancestries in Papuans. Cell, published online April 11, 2019; doi: 10.1016/j.cell.2019.02.035
