Why did people go out of Africa?

Simulations have identified several possible reasons our ancestors left Africa. However, it is far from exhaustive; so the ultimate cause is still a mystery


Humans evolved in Africa around 200,000 years ago. But we didn’t hang around. By 100,000 years ago we had begun spreading throughout the world.

This journey was long, arduous, and took them to unfamiliar environments. So why did they bother?

What drove our ancestors to leave their homeland in Africa and travel further than any primate has before?

Who, what, when, where?

We know a lot about our ancestors’ migration out of Africa, from a lot of different sources.

Through genetics we know when they left the continent and what route they took. Fossil evidence backs this up, documenting humans appearing in the Middle East – for example – around the time they should.

The route out of Africa as documented by genetic data

The route out of Africa as documented by genetic data

Mites also back up this history. Humans have mites living on their body at all times. The family tree of these mites matches up very nicely with the family tree of humans. It shows an ancient home in Africa, followed by a migration around the world.

All sorts of data from all sorts of surprising sources attest to our spread out of Africa. As a result there’s an awful lot about our species’ movement we do know, yet there are still some key questions that remain a mystery. Questions like . . .

Why leave Africa?

We know a lot about our ancestors’ migration out of Africa. But we don’t know much about the why they undertook this difficult trip.

Part of this may be because there was no real migration out of Africa. As a population grows it naturally spills over into the surrounding area. Over time it just keeps expanding, following viable environments. Before long the humans have spread around the whole world. Just as a bi-product of demography.

Computer simulations have confirmed that this is one possible explanation for this migration. Demographic pressures would be enough to force humans on a very long journey (albeit, over a very long time). However, they also identified several other key factors that may be involved.

  1. Environmental change could have made it viable for people to move into new regions.
  2. Demography alone could have been the cause. Populations naturally filled up regions, forcing movement into new ones. This caused a gradual spread out of Africa over many generations.
  3. New resources could have made regions outside of Africa attractive. Other animals naturally spilled out of Africa as they filled up environments, and some humans just followed them on this journey.
  4. Humans could have deliberately decided to move. Perhaps some combination of the above factors encouraged people to migrate, rather than gradually, naturally expanding.

Other explanations

Of course, these simulations weren’t an exhaustive list of reasons to leave Africa.

As such, there could be additional explanations not considered. For instance, Africa saw an awful lot of environmental change in the time leading up to the great human migration. This may have forced humans to adapt and develop new technology and behaviours. Effectively, they would have been “pre-prepared” for the migration.

Others have suggested that the migration out of Africa may have been a lot more deliberate than these simulations suggest. Our ancestors’ prey may have been moving out of the continent. These early humans just naturally followed after them.

In short, why our ancestors left Africa is still a mystery.

Simulations have helped identify some plausible explanations. But this examination is far from exhaustive. There is still an awful lot more research on the topic that needs to be done. Perhaps the real explanation has already been identified. Perhaps it is a combination of some of them. But without more work we won’t know for sure.

tl;dr

Simulations have identified several possible reasons our ancestors left Africa. However, this list is far from exhaustive; so the ultimate cause may still be a mystery.

References

Grove, M. (2014). Palaeoclimates, plasticity, and the early dispersal of Homo sapiens. Quaternary International

Hölzchen, E., Hertler, C., Timm, I. and Lorig, F., 2015. Evaluation of Out of Africa hypotheses by means of agent-based modeling. Quaternary International.

Palopoli, M.F., Fergus, D.J., Minot, S., Pei, D.T., Simison, W.B., Fernandez-Silva, I., Thoemmes, M.S., Dunn, R.R. and Trautwein, M., 2015. Global divergence of the human follicle mite Demodex folliculorum: Persistent associations between host ancestry and mite lineages. Proceedings of the National Academy of Sciences, 112(52), pp.15958-15963.

Related Articles

15 thoughts on “Why did people go out of Africa?”

  1. john zande says:

    What’s the current thoughts on Australian settlement, considering Lake Mungo (southeast Australia) has revealed findings that have been dated, if I remember correctly, to 60,000 BPE?

    1. Adam Benton says:

      It turns out that may have been part of an earlier, successful migration.

      http://www.evoanth.net/2015/08/11/aboriginal-australians-result-of-earlier-migration-out-of-africa/

  2. Cynthia Echterling says:

    Because it was there.

    1. Adam Benton says:

      These models all fail to take into account a notion of human agency. It’s all treated as side effects of natural processes. The real question is whether that is a notion worth considering.

  3. Charles A. Bishop says:

    There were earlier movements out of Africa beginning well over a million years ago by Homo erectus, and probably many others over the thousands of years after. Certainly population pressure in pursuit of resources is a good possibility after 100,000 years ago. Improved hunting technology may have been another reason even though it doesn’t show up well in the archaeological record during the period from 100,000 to 40,000 years ago. And, of course, there were major environmental changes over time. Humans are also curious animals, always wanting to know what is over the next hill or at some distant point. Multiple factors explain all movements but the importance of each may vary over time .

    1. Adam Benton says:

      It would certainly be interesting if it was possible to track how these motivations changed over time. Did curiosity drive AMH more than Homo erectus, for example?

      1. Charles A. Bishop says:

        Your question is valid. Unfortunately, the evidence at this time is too sparse to draw any firm conclusions about motivations, but this may change as more is learned.

  4. Marcel Williams says:

    For the same reason that other animals radiate to other geographic regions on our planet.

    But Homo first radiated out of Africa more than 2 million years ago.

    Marcel

  5. Wyrd Smythe says:

    The desire to see what lies beyond the next hill goes pretty far back in our culture. Ape-like curiosity in a more thoughtful species… I do think the notion is well worth considering.

    1. Adam Benton says:

      It would be certainly interesting if we could identify how much agency was involved in this sort of thing. How much of it was just a bi-product of demography, and how much was intentional?

    2. Charles A. Bishop says:

      Yes, the pursuit of animals and other foods was one reason but certainly curiosity must have been another factor. Still another reason may have been conflict and competition within groups causing families to break off and move further on. Motives don’t show up well in the archaeological record, but one or more of the above reasons probably explain migrations. These were probably the same reasons that explain the populating of the Americas after about 15,000 years ago.

      1. Adam Benton says:

        Modern hunter-gatherer groups will split up if they get too big (or environments change so it can’t sustain as large groups). There doesn’t have to be any direct conflict between individuals.

        1. Charles A. Bishop says:

          Yes, conflict is rare within small extended family groups because everybody is related and cooperation and sharing are very important to survival. But if the group grows too large for the resources, an extended family may break of and expand into a new habitat. This is another way that populations can come to occupy new areas.

  6. hari says:

    All these benign explanations do not substantiate the crossing of oceans and the speed of spread of the modern human ancestors across the world. We need to compare average rate of migration of a burgeoning animal population with that of modern man to really appreciate the causes fuelling the spread

    1. Adam Benton says:

      In many places humans migrate into a region around the same time as other species suggesting we have a similar migration rate to most animals

Leave your filthy monkey comments here.

More in Ancient technology
Why did God evolve?

Belief in a law-giving god is thought to encourage co-operation. Cross cultural data confirms this. Also, religious people have lower sexual permissiveness

Close