[JOSEPH HENRICH:] Think back to when humans first got the capacity for cumulative cultural evolution—and by this I mean the ability for ideas to accumulate over generations, to get an increasingly complex tool starting from something simple. One generation adds a few things to it, the next generation adds a few more things, and the next generation, until it’s so complex that no one in the first generation could have invented it. This was a really important line in human evolution.
Another example here is fire and cooking. Richard Wrangham, for example, has argued that fire and cooking have been important selection pressures, but what often gets overlooked in understanding fire and cooking is that they’re culturally transmitted—we’re terrible at making fires actually. We have no innate fire-making ability. But once you got this idea for cooking and making fires to be culturally transmitted, then it created a whole new selection pressure that made our stomachs smaller, our teeth smaller, our gapes or holdings of our mouth smaller, it altered the length of our intestines. It had a whole bunch of downstream effects.