we don't know exactly where the encounter between this denisovan-like population and the modern humanopulations occurred. it's possible that this mutation was present in the denisovan-like population but was not advantageous, yet after the mixing between these two, and the modern human population moved to high altitude, it became advantageous. narrator: this important dna variant, or allele, from an extinct human ancestor, is part of the genetic inheritance of himalayan people today. di rienzo: the finding was very exciting. it's telling us something more than just the fact that modern humans and denisovans mixed, but also that denisovans gave modern humans an allele that allowed them to conquer this so-called third pole, and to adapt to these very harsh conditions of high altitude hypoxia. narrator: genetics and the study of ancient dna allow us to see modern human evolution in action. warinner: this new ability that we have to actually sequence ancient genomes is teaching us so much we didn't know about human history and prehistory. so, already, we're rewriting the storybook of huma