Single wave of migration from Africa peopled the globe

A Maltese research fellow at the University of Cambridge has contributed to an article that made it to Science Magazine’s Top Ten list of Scientific Breakthroughs for 2016:

The article in which Alexia Cardona took part was published in Nature last October:

The main highlight of the paper was that Ms Cardona and her team found genetic evidence that another human migration happened out of Africa around 120 thousand years ago, a trace of which still exists in the current aboriginal Papuans.

The story of our species is driven by wanderlust. Born in Africa, Homo sapiens expanded into the far corners of the globe in the past 100,000 years, meeting and mingling with more archaic hominins already living there. But researchers have long debated how and when modern humans left Africa: Was it in a single migration or in repeated waves?

In 2016, a burst of genomic data all but clinched the case that most living people outside Africa descend from a single migration; any earlier migrations were mostly swamped by this last wave.

In a trio of studies, researchers worked with aboriginal groups to collect and analyze hundreds of genomes from people living in farflung corners of the world, including previously scarce samples from Australia, Papua New Guinea, and Africa. They tracked the ancient branching of populations recorded in the DNA.

One study analyzed 83 genomes from Australia, long considered a place apart. The DNA showed that, in contrast to previous suggestions, Australia was initially settled only once. Moreover, the ancestors of Aborigines and Eurasians split from Africans around the same time, possibly about 70,000 years ago, suggesting a single exodus from Africa before the split.

An independent study analyzing 300 genomes from 142 populations also reported a single wave out of Africa, which diverged into all living non-Africans starting perhaps 50,000 years ago, although the dates are imprecise.

The third study, which analyzed 379 genomes from 125 populations, reported mostly this same pattern, with a wrinkle: About 2% of the genome of Papua New Guineans may stem from a separate, earlier migration out of Africa, perhaps 100,000 years ago.