Razib Khan looks at where modern humans came from in light of recent genetic analyses, and how the Toba eruption 74,000 YBP gave our particular lineage an opening our ancestors exploited, wiping out the competing varieties of humans within 10,000 years:
The most powerful explosion of the last 2.5 million years, the Toba eruption triggered a decade-long cold snap that wrought havoc even amid the last Ice Age’s already inclement conditions. When the cataclysm hit, Neanderthals had reigned supreme from the Atlantic to the Siberian Altai for hundreds of thousands of years, while their Denisovan cousins dominated East Asia. To the south, diminutive small-brained human populations occupied Indonesia’s Flores islands and Luzon in the Philippines, coexisting with both modern humans and Denisovans. But thirty thousand years after Toba, a blink of the eye in geological time, the landscape of human geography was abruptly transformed. Neanderthals, Denisovans and Southeast Asia’s enigmatic hominins were extinct or under extreme, terminal pressure from African newcomers. Neanderthals, by then resident in Europe for over 500,000 years, disappeared 5,000 years after that mass arrival of African humans to northwest Eurasia. Denisovans, by then as far into their East Asian sojourn as Neanderthals their western one, disappeared soon after their cousins. Finally, the small human populations of Flores and the Philippines also died out 50,000 years ago, after modern humans’ final expansion. This radical homogenization of Eurasian humanity is associated with the expansion of the Initial Upper Paleolithic (IUP) archaeological culture, which radiated out of the Middle East 50,000 years ago, washing over the whole of Asia, Europe and Australia by 45,000 years ago.
Our naive late-20th-century idea held that a single modern tribe burst out of East Africa 50,000 years ago, replacing Neanderthals and other human lineages inexorably and in totality. In reality, almost all modern humans have some Neanderthal ancestry, while Denisovans contribute nearly 4% of the genome of Papuans and other Melanesians. But it remains true that the entire world’s genetic legacy outside Africa today does come from a single intrepid tribe, a lone population with a unified early history. But these were not the first Africans to venture out of their ancient homeland; they were the last.
He includes a flow chart of human genetic lineages following the Neandersovan exit from Africa 650,000 YBP, and it has more dotted lines than a Fortune-500 org chart.