A cave in the Altai where, in 2008, DNA extracted from a child's finger bone revealed an entire unknown human species — the Denisovans. Their genes are still carried by people in Melanesia and Tibet, the Tibetans having inherited a variant that helps at altitude. One layer held the remains of a girl whose mother was Neanderthal and whose father was Denisovan — the only known first-generation person of two different human species.