Barbarians at the Border
The migrant story is a little more nuanced than Elon Musk might have you believe.
About 200,000 years ago, a woman was born whose mitochondrial DNA became the source DNA of every person alive today. All of us are her descendants. At that time, the modern human population was small — about 10,000–20,000. It would later ebb and flow but never get as small as the 1,280 breeding-age individuals that our Simian ancestral population averaged in Africa some 900,000 years ago.
Hominid populations expanded to perhaps 2.5 million 70,000 years ago. Then we hit a bottleneck. The Toba supereruption in Indonesia plunged global mean temperature by 2.3°C (4.1 °F) and the cold lasted perhaps 1000 years. Deprived of food, our human ancestors were nearly extinguished. A few thousand made it through that dark age. Genetic bottlenecks from Toba have also been shown to have occurred in populations of chimps, macaques, cheetahs, and tigers.
Analyses of mitochondrial DNA have estimated that a major migration from Africa occurred during the Toba catastrophe. Small bands crossed the Red Sea to Yemen and followed the coast into the Levant (Sinai/Syria/Jordan/Persia), Southeast Asia, and Oceania. Other trails branched off to the West, into Europe. Along the way, H. sapiens interbred with Neanderthals and Denisovans and left…