Was there a transfer of genes from modern humans into Neanderthals?


Was there a transfer of genes from modern
Humans into Neanderthals ? The analysis was focused on two genomes extracted
from bones in an ancient Altai cave, with one genome belonging to the Neanderthals,
the other genome belonging to the Denisovans. Both genomes showed high amounts of homozygous
stretches suggesting a long-term decline in population size. Neanderthals and Denisovans diverged at least
about 500 000 years ago from modern humans and about 400 000 years ago from each other. Modern non-african humans obtained genes from
Neanderthals about 60 000 years ago and gene flow from Denisovans to modern humans has
also been described. In this context the current study asked, whether
there was also gene flow in the other direction, from modern humans into Neanderthals. For this aim 15581 sequences of 100 kB length
from the Neanderthal and Denisovan genomes were compared with respective stretches from
modern African genomes. The Neanderthal genome contained stretches
with a low divergence to modern Africans but a relatively high divergence to the Denisovan
genome. According to computer modelling this observation
is best explained by asuming the introgression of genes from modern humans into the Altai
Neanderthal genome. A comparison of sequence information of these
genes from modern Africans and Altai Neanderthals suggests that the genes have been transferred
at least 100 000 years ago. This excludes the participation of the ancestors
of today’s non-African humans, which left Africa only 60 000 years ago. Instead, mating between modern humans and
ancestors of the Altai Neanderthals may have occured in the Middle East, where early modern
humans have lived more than 100 000 years ago. DNA-probes from modern humans recognized more
regions in DNA from Altai Neanderthals when compared to DNA from Neanderthals from Spain
or Croatia, suggesting that this group of Neanderthals obtained a particularly large
amount of genes from early modern humans.

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