Question: If us as a human race started off in Africa how did we develop the intelligence to spread out all across the world

Susan Cartwright answered on 18 Jun 2015:

Spreading all across the world doesn’t necessarily require intelligence – many species are very widespread. However, it is true that humans are the most widely distributed large animal in the world, not because it takes intelligence to spread, but because it takes intelligence to survive in environments you didn’t evolve for – for example, the Arctic. It also took intelligence to get to Australia: that required a sea crossing, i.e. boats.

It appears that we developed intelligence in Africa: the oldest fossils of modern humans come from there. In fact, at least two distinct species of humans came from Africa and then spread all over the world: modern humans (Homo sapiens) and the older Home erectus, which at least colonised Asia and Europe, though it probably didn’t get to America or Australia.

We developed intelligence because we needed it to survive – as predators, we are frankly not very good compared to lions, leopards, hyenas etc., but we make up for it by using tools and being clever in our hunting techniques, e.g. working together more effectively than lions do. It appears to have been partly driven by climate change: the bit of Africa we come from stopped being covered by jungle and became open plains, which forced us to change our way of life.

Note that we almost didn’t make it: as a species, we have rather little genetic diversity compared to most species (despite our very varied appearance, which is actually caused by differences in a rather small number of genes). This implies that at some point in our history, we were an endangered species, with only a few thousand of us left. We made it through – but we could easily not have done!