70,000 Years Ago Humans Underwent A Major Shift – That’s Why We Exist

Arthur T Knackerbracket has processed the following story:

Humans come from Africa. This wasn't always obvious, but today it seems as close to certain as anything about our origins.

There are two senses in which this is true. The oldest known hominins, creatures more closely related to us than to great apes, are all from Africa, going back as far as 7 million years ago. And the oldest known examples of our species, Homo sapiens, are also from Africa.

It's the second story I'm focusing on here, the origin of modern humans in Africa and their subsequent expansion all around the world. With the advent of DNA sequencing in the second half of the 20th century, it became possible to compare the DNA of people from different populations. This revealed that African peoples have the most variety in their genomes, while all non-African peoples are relatively similar at the genetic level (no matter how superficially different we might appear in terms of skin colour and so forth).

In genetic terms, this is what we might call a dead giveaway. It tells us that Africa was our homeland and that it was populated by a diverse group of people - and that everyone who isn't African is descended from a small subset of the peoples, who left this homeland to wander the globe. Geneticists were confident about this as early as 1995, and the evidence has only accumulated since.

And yet, the physical archaeology and the genetics don't match - at least, not on the face of it.

Genetics tells us that all living non-African peoples are descended from a small group that left the continent around 50,000 years ago. Barring some wobbles about the exact date, that has been clear for two decades. But archaeologists can point to a great many instances of modern humans living outside Africa much earlier than that.

What is going on? Is our wealth of genetic data somehow misleading us? Or is it true that we are all descended from that last big migration - and the older bones represent populations that didn't survive?

Eleanor Scerri at the Max Planck Institute of Geoanthropology in Germany and her colleagues have tried to find an explanation.

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