Modern humans evolved in Africa, before spreading around the whole world. But we weren't the first member of our family to do so. Nearly 2 million years ago, Homo erectus also stepped out into the big wide world. How did they manage to make this difficult journey into uncharted territory? It turns out they succeeded by playing it safe.
Investigations into their new homes out of Africa has revealed Homo erectus wasn't exactly a pioneer. Rather, they simply followed their prey as those species were expanding into the rest of the world. And as they migrated, they tended to stick to areas where resources were readily available and predators scarce. Only later, when they developed new tools, did they begin to take the initiative when exploring.
Whoever said discovery had to be hard work?
Fast moving Homo erectus
The earliest Homo erectus fossils indicate they evolved around 1.9 million years ago, somewhere in Africa. However, within a few hundred thousand years we begin finding evidence of them outside of this heartland. Places like Dmanisi in Georgia (famous for showing there was only one species of Homo erectus) and a plethora of Chinese sites show H. erectus was outside of Africa by ~1.8 million years ago.
This rapid expansion is rather perplexing. H. erectus was a hominin very similar to us, able to walk upright very well, manufacture and use tools, and with a brain bigger than the more ape-like hominins that had come before. However, that brain wasn't much bigger and their tools weren't any more advanced. They didn't even have control over fire at this point.
Later in their history many of these features would evolve. Their brain continued to increase in size, almost doubling over the course of their time on earth. They also developed new tools, including fire and the famous Acheulean handaxe; a multipurpose tool that could be used for just about anything you needed. But of course, they didn't leave Africa after these developments evolved. They left right at the beginning of their history, before they got their hands on handaxes and big brains in their noggins.
So how come they were able to leave Africa with a similar setup to earlier species; who didn't migrate out of our homeland. The most significant difference between Homo erectus and earlier species is locomotion. Was that it? Or were the small changes in brain size enough? Or did all three factors make the big difference?
Or maybe the movement out of Africa wasn't as difficult as it first seemed.
Taking the easy route
What if it wasn't Homo erectus that changed and made it possible for the species to migrate out of Africa. What if the conditions outside of Africa became more habitable; allowing Homo erectus to migrate despite its relative lack of change? This idea has been thrown about for a long time, although no previous reaseach has been able to conclusively show if its true or false.
At least, until June 2016. Then, a group of researchers from instituions around the world carried out what is arguably the largest investigation into the migration of Homo erectus. Rather than focusing on the hominin, they looked at other mammals that were also leaving Africa around this time (and the environment they inhabited) from over 500 sites across the Old World.
Based on all this, they were able to get a pretty good picture of what the environment outside of Africa was like at this time. In turn, they could figure out how habitable it would be for Homo erectus. Where did their prey live? Where were their predators? What was the environment like, and where could they find water and other resources they needed?
This allowed them to plot various routes out of Africa for our hominin relatives. They could examine the route they might take if they were awesome and not limited by the environment. Or if they were having a tougher time of their migration, and forced to stick to locales extra favourable to them. When they compared these predictions to the actual route Homo erectus took they found it was much more similar to the latter. They stuck to regions where carnivores were rare, raw materials easy to come by, their prey was common, and the environment recognisable.
In other words, they took the easy route out of Africa.
Changes in tools
All of this explains how Homo erectus was able to migrate around the world despite not having many of the adaptations we associate with later, adaptable hominins. However, it wasn't long before they began to acquire some of these characteristics. Their brains continued to increase in size and within a few hundred thousand years they had their hands on the Acheulean handaxe. An adaptable bit of kit useful in almost any situation. Depending on whom you ask, they might also have had fire as well.
These developments also coincide with their migration into Europe, an area they had previously avoided. When you look at the mammals of Europe (and the associated environments), you find this region was a lot less hospitable to Homo erectus. But they didn't care. They moved in anyway. In particular, they seem to have stopped caring about predators, which had dictated their migration into Asia.
Homo erectus was back with a vengence.
Summary
Homo erectus was the first member of our family to leave Africa. It only turns out they did so because climate change made the environment more habitable for them. Only later, after they invented new technology, did they begin to occupy tougher places outside of Africa.
References
Boyd, R., Silk, J.B., Walker, P.L. and Hagen, E.H., 2000. How humans evolved. New York: WW Norton.
Carotenuto, F., Tsikaridze, N., Rook, L., Lordkipanidze, D., Longo, L., Condemi, S. and Raia, P., 2016. Venturing out safely: The biogeography of Homo erectus dispersal out of Africa. Journal of human evolution, 95, pp.1-12.
Slatkin, M. and Racimo, F., 2016. Ancient DNA and human history. Proceedings of the National Academy of Sciences, 113(23), pp.6380-6387.
Yang, S.X., Hou, Y.M., Yue, J.P., Petraglia, M.D., Deng, C.L. and Zhu, R.X., 2016. The Lithic Assemblages of Xiaochangliang, Nihewan Basin: Implications for Early Pleistocene Hominin Behaviour in North China. PloS one, 11(5), p.e0155793.
