Recent sequencing of Neanderthal and Denisovan genomes shows that some admixture with these populations has occurred . Modern humans outside Africa have 2 – 4 % Neanderthal alleles in their genome , and some Melanesians have an additional 4 – 6 % of Denisovan alleles . These new results do not contradict the " out of Africa " model , except in its strictest interpretation , although they make the situation more complex . After recovery from a genetic bottleneck that some researchers speculate might be linked to the Toba supervolcano catastrophe , a fairly small group left Africa and interbred with Neanderthals , probably in the Middle East , on the Eurasian steppe or even in North Africa before their departure . Their still predominantly African descendants spread to populate the world . A fraction in turn interbred with Denisovans , probably in south-east Asia , before populating Melanesia . HLA haplotypes of Neanderthal and Denisova origin have been identified in modern Eurasian and Oceanian populations . The Denisovan EPAS1 gene has also been found in Tibetan populations . Studies of the human genome using machine learning have identified additional genetic contributions in Eurasians from an " unknown " ancestral population potentially related to the Neanderthal-Denisovan lineage
Toba supervolcano catastrophe
Toba catastrophe theory
Human evolution