Denisova Cave, Altai Mountains, Siberia
At various times the Denisova Cave has been occupied by modern humans, Neanderthals and the eponymous Denisovans. For the latter we have too few bones to reconstruct a skeleton yet enough DNA to explore the genome (here). The results indicate that there was gene flow between Denisovans and modern humans as previously shown for Neanderthals.
In a preliminary report (here) we learn that a group led by Svante Pääbo has sequenced the genome of the Neanderthals that lived at Denisova. They were a population distinct from those in Croatia and the Caucasus (for which there also is genomic data). Interbreeding between humans and Neanderthals is more likely to have occurred in the Caucasus than at Denisova.
Intriguingly, however, the study found evidence of interbreeding between the local Neanderthals and the Denisovans and - even more remarkably - evidence of contribution to the Denisovan gene pool of yet another hominin.
Possible significance for human reproduction
The highly polymorphic HLA class-I antigens (HLA-A, -B and -C) play important roles in the immune response to infection as well as in reproduction. A previous study (here) showed that interbreeding with archaic populations, and subsequent conservation by natural selection, has made a significant contribution to the HLA system in human populations outside Africa.
Some of the introgressed HLA allotypes code for proteins that are ligands for killer-cell immunoglobulin-like receptors (KIRs) including ones thought to be important in relation to human reproductive failure (here).
Work is in train to align the genomes of the chimpanzee, Neanderthals, Denisovans and modern humans. The secrets revealed by the remains from Denisova may ultimately contribute to our understanding of human reproduction.