A New Theory of Humanity's Origins

Despite popular depictions, humanity likely didn't originate out of one population. (Source: Warner Bros.)

The “Out of Africa” hypothesis, or the clunkier Recent African Origin of Modern Humans, is the near-universally accepted theory of our species’ origin, but how exactly we got started remains debated. The earliest human remains are known to the north of the continent, dating to over 300,000 years ago, but the fossil record only tells us so much about the diverging branches of the Homo genus tree. It’s been long held that human beings owe their origins to one specific population that diverged from an archaic human ancestor, but a genetics-based study published this week in Nature has challenged this idea.

These recent findings suggest Homo sapiens are the product of two divergent populations, not one as had been accepted. This is based on genomic sequencing from contemporary Africans across the continent, whose genetic makeup is best explained by two distinct branches that nonetheless interbred with each other. These findings are limited insofar as they can’t say where exactly these populations lived, but they being distinct from each other supports a geographical separation. The projected timeline suggests these two branches existed alongside each other for about a million years, before converging 120,000 years ago and later migrating out of the continent.

Genetic diversity in modern-day Africa.

The study drew from four possible genetic models to explain the origins of Homo sapiens: a “single-population expansion, single-population expansion with regional persistence, archaic hominin admixture and multi-regional evolution.” It found that two distinct populations best explains the genetic diversity exhibited by contemporary Africans, bolstered by additional interbreeding with Neanderthals who originated about 500,000 years ago. The jump to Homo sapiens likely happened more than once independently, resulting in the divergent genetic makeup of populations living in Northern Africa and the Horn of Africa today.

An analog to our species’ beginning might be found in the K/Pg extinction event. Just as we now know the Age of Dinosaurs ended in a long whimper and not a climatic bang, our species began slowly across a period of a million years, with no one single origin point. It is unlikely we will ever have a perfectly clear image of the dawn of our species. Genetic findings can give us the big picture, and the fossil record provides case examples, but there will always be gaps in our knowledge of that bridge between humanity and the rest of the animal kingdom.