The Origins of Complex Human Behavior

Until recently the first evidence that modern humans were behaviorally different from other hominids dated to around 70,000 years ago. Modern humans could be traced via their skeletons back more than 200,000 years, but so far as archaeologists could tell, they continued to make the same sorts of tools and generally live in the same way as their ancestors. Then, rather suddenly, things changed: tools became more complex, the first shell beads and other ornaments appeared, along with the first clear evidence of ritual behavior. People wrote about a "Big Bang," a sudden transformation of human potential, and the most influential theory equated this dramatic change with the invention of modern language.

But many archaeologists, including me, were always skeptical of this conclusion. Since language seems coded into our genes, how could it have been invented at some point in time? Ritual behavior likewise seems deeply human. Surely such things ought to have evolved over hundreds of thousands of years. This only became more of a problem when genetic studies failed to find any substantial genetic change that could have served as the trigger for this revolution.

And yet, evidence of those posited gradual changes was very hard to come by, limited to a few hints from sites with disputed dating or interpretation. Until this week:

The latest evidence comes from the Olorgesailie Basin in Southern Kenya, where researchers have previously found traces of ancient relatives of modern human as far back as 1.2 million years ago. Evidence collected at sites in the basin suggests that early humans underwent a series of profound changes at some point before roughly 320,000 years ago. They abandoned simple hand axes in favour of smaller and more advanced blades made from obsidian and other materials obtained from distant sources. That shift suggests the early people living there had developed a trade network — evidence of growing sophistication in behaviour. The researchers also found gouges on black and red rocks and minerals, which indicate that early Olorgesailie residents used those materials to create pigments and possibly communicate ideas.

Obviously this is not the strongest possible evidence, I mean, a lot of things can gouge a red rock. But if these changes were gradual, then the early stages ought to be very hard to detect. I look forward to a lot more evidence emerging in the future, along with a better understanding of the long, slow process by which we became human.