Check it out, hot off the press:
Nepalese Sherpas inherited ability to thrive in high altitudes from extinct humans
Meredith Knight | July 3, 2014 | Genetic Literacy Project
On their way out of African homo sapiens likely bred with Denisovans somewhere in central Asia where some of the progeny picked up the EPAS1 mutation. For those homo sapiens that migrated to high altitudes, the gene variant was advantageous, so it spread quickly through the population and just kept going. “What we’re learning from ancient genomes is that while each of them may have contributed only a little to our ancestry, those genetic streams were full of tiny golden nuggets of useful genes,” anthropologist John Hawks told Yong.
There is precedent for this kind of interspecies breeding in hominids with direct, beneficial genetic effect, Catherine Brahic points out:
Humans interbred with Neanderthals soon after moving out of Africa, when we were ill-equipped to cope with Eurasian diseases. However Neanderthals had been hanging out in Europe and Asia for much longer, so their immune systems had adapted. There is evidence that humans snagged some of the Neanderthals’ immunity genes when the two mated, perhaps helping us to spread across the planet.