1.6 million years ago
Turkana Boy (KNM WT 15000), from West Turkana, Kenya, is a striking find: the most complete early human skeleton we’ve got.
In addition to confirming a lot about Homo erectus’s shift to not-totally-unlike-modern bipedalism, he also seems to be telling us something about Homo erectus’s not-really-modern-human life history. Turkana Boy is not a grown up, but he has his second molars erupted. If he were a modern human, this would make him about 12 years old. Based on this, a lot of earlier accounts on the kid suggested he had a lot of growing to do, and would have ended up being a really tall adult – over 6 feet. But the latest evidence is that he was only 8-9 years old when he died, and wouldn’t have grown much taller than his 5 foot 3 if he had lived. In other words, Homo erectus back in his day grew up a lot more quickly than modern humans, and probably didn’t have much of the secondary adolescent growth spurt (coming after a late childhood slowdown) that we see in modern humans.
This in turn, if it holds up, is telling us that life was a lot rougher back then. Humans hadn’t got their act together keeping juvenile mortality low, and there was still strong pressure to rush through childhood and get on to reproducing quickly. A lot of kids, like Turkana boy, didn’t make it.