People living in the highlands and lowlands of Papua New Guinea have different frequencies of several Denisovan genetic variants, which may help them adapt to their local environmental conditions.
The Denisovans were hominins that lived across eastern Eurasia for hundreds of thousands of years, giving them plenty of time to adapt to a variety of environments.
After leaving Africa, Homo sapiens听interbred with other human species, including Denisovans, allowing them to acquire useful genetic adaptations to Eurasian climates. For example, most modern Tibetan people living at 4000 metres above sea level have the Denisovan version of the gene EPAS1, which helps them cope at high altitudes where there is little oxygen.
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Denisovans are mysterious because only a handful of their remains have been found. Identifying Denisovans鈥� genetic variants, or alleles, in modern humans can give clues about where they lived and what they were like.
A promising place to look for this archaic DNA is Papua New Guinea, where 3 to 4 per cent of living people鈥檚 DNA comes from Denisovans, compared with 1 to 2 per cent in people of Eurasian ancestry.
at the University of Tartu in Estonia and his colleagues compared the genomes of 128 people from two Papua New Guinean populations: lowlanders from 100 metres above sea level and highlanders from approximately 2500 metres above sea level. By looking at maps of the genetic material each population inherited from Denisovans, the researchers could uncover whether they had specific alleles that might have helped them adapt to their particular environments.
The team found that some of the Denisovan gene variants only found in the highlanders appear to be associated with early brain development, including variants of genes called NEUROD2 and PAX5. They speculate that these alleles might help the highlanders adapt to the lower availability of oxygen at high altitude.
It is interesting that the Denisovan EPAS1 allele found in Tibetan people was completely absent from the Papua New Guinean highlanders, says Yermakovich. 鈥淚t was not there at all, not even in low frequencies,鈥� he says. This could be because of random chance. 鈥淚f EPAS1 was not transmitted from Denisova to the ancestors of Papuan highlanders, then it can鈥檛 be selected,鈥� says at the University of Turin in Italy, another member of the study team.
But this could also show that the impact of Denisovan DNA may vary at different altitudes, says Andr茅. Studying groups from different altitudes and locations can help us understand the diversity of genes humans inherited from Denisovans, she says.
The researchers also found that lowlanders have much higher frequencies of Denisovan variants for the genes GBP1, GBP2, GBP4听and GBP7, which code for proteins important to the immune system. Because diversity is key when it comes to the immune system, having Denisovan versions of genes related to pathogen response is probably very helpful for people in lowland parts of the country, as there than it is in the highlands.
The fact that Denisovans had these genetic variants doesn鈥檛 mean they had the same local adaptations that Papua New Guineans have today, though, says at the Max Planck Institute for Evolutionary Anthropology in Germany. 鈥淭he effect of genes can change with the environment and through time, so it鈥檚 not necessarily that something that is adaptive now was adaptive 20,000 years ago.鈥�
But the very strong differences in frequency found among the highlanders and lowlanders does suggest there was some directionality in how these changes in frequency occurred, says Peyr茅gne. Archaic DNA appears to have adaptive benefits for both populations that are still useful today, he says.
PNAS
