Biology Magazine

Where Did Modern Humans Evolve? It’s Complicated

Posted on the 06 September 2018 by Reprieve @EvoAnth

You've probably heard that modern humans evolved in Africa. This is true, but not the most useful answer. After all, Africa is a ruddy big place 1.

So, can we be any more specific?

An African heritage

We know our species evolved in Africa sometime in the last half a million years. The evidence for this is overwhelming. In fact, it just might be too overwhelming.

See, we've got a fair few fossils from this time period. Most recently, we found some human fossils in Morocco. These were some of the oldest found, so are a bit different to us, as you might expect. They have a larger face with a jaw that sticks out and prominent brow ridges. Their braincase is long and low, similar to earlier human species 1.

Where did modern humans evolve? It’s complicated

Meanwhile, in East Africa, we've got the Omo Kibish fossils. One has a big brow ridge, like the Moroccan skull, but their brain case is tall and round, more like ours. Another fossil is the reverse, featuring a long, low brain case but much-reduced brow ridges. Elsewhere in Ethiopia, the Idaltu fossils have a weird hybrid braincase, being both round like ours yet long like the other hominin species. This combines to give them one of the biggest brain sizes ever recorded 1.

Then we get to South Africa, where we've found a skull at Florisbad. It's got the big face of the Moroccan skull, but the brow ridges are less prominent. Other fossils from the region follow yet a different pattern, mixing and matching brow ridge prominence, degree the jaw sticks out, and skull shape 1.

And these are just the fossils I can be bothered to describe. There's many more out there, each with a slightly different combination of traits 1.

Multiregional modern humans

Starting to see what I mean by too much evidence? It's all over ruddy Africa! To make it more confusing, each population seems to be taking a different evolutionary route 1. Which, if any, led to us?

It seems there's no clear frontrunner for the location where modern humans evolved. We're not even sure what evolutionary route they took. But maybe that's the point. What if humans evolved all over Africa?

This is the hypothesis put forward in a recent paper by Scerri et al. They suggest that there were little pockets of early Homo sapiens all over the continent. Every so often these pockets might meet and share DNA (as humans love to do) but were otherwise fairly isolated. Somewhere amongst all this mess, we evolved. Bits and pieces of us evolving, spreading, and combining across a whole continent over hundreds of thousands of years 2.

Scerri et al.'s hypothesis help to explain all this weird anatomical variation we see across early Homo sapiens in Africa. We also see similar regional patterns in technology from this time. Which again, makes sense if we're dealing with a bunch of isolated groups of people 2.

But as well as just explaining stuff, this hypothesis also raises some interesting possibilities about our evolution.

Mating with Homo naledi

See, we know early Homo sapiens weren't the only bunch of humans running around Africa at this time. The recently discovered Homo naledi was in South Africa during this period, and there may have been some Homo erectus and Homo heidelbergensis elsewhere 2.

Memorising all those names and places isn't that important. What is important is that if we're dealing with a bunch of isolated human groups who occasionally bumped into each other, maybe some of us also bumped into those other species. In more ways than one, if you know what I mean 2.

Modern humans are the odd ones out in the human family, with weird round heads and a prominent chin. Maybe a unique pattern of hybridisation - both with our multiregional groups and other species - explains our unique features 2.

This is just one fascinating possibility that's raised - and could be used to test - this new hypothesis. What brought these divided human populations together? Perhaps environmental change opened up or closed off corridors between us. How old is our species? And where did it we first come from 2?

Our origin may be way more complicated than we ever thought. But that's super exciting.

References

  1. Stringer, C., 2016. The origin and evolution of Homo sapiens. Phil. Trans. R. Soc. B, 371(1698), p.20150237.
  2. Scerri, E.M., Thomas, M.G., Manica, A., Gunz, P., Stock, J.T., Stringer, C., Grove, M., Groucutt, H.S., Timmermann, A., Rightmire, G.P. and d'Errico, F., 2018. Did our species evolve in subdivided populations across Africa, and why does it matter?. Trends in ecology & evolution.
  3. Gibbons, A. (2017). World's oldest Homo sapiens fossils found in Morocco. Science. https://doi.org/10.1126/science.aan6934

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