A conversation with Joseph Henrich in Edge:
[JOSEPH HENRICH:] The main questions I've been asking myself over the last couple years are broadly about how culture drove human evolution. 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, and we've begun to pursue this idea called the cultural brain hypothesis—this is the idea that the real driver in the expansion of human brains was this growing cumulative body of cultural information, so that what our brains increasingly got good at was the ability to acquire information, store, process and retransmit this non genetic body of information. The two systems begin interacting over time, and the most important selection pressures over the course of human evolution are the things that culture creates—like tools. Compared to chimpanzees, we have high levels of manual dexterity. We're good at throwing objects. We can thread a needle. There are aspects of our brain that seem to be consistent with that as being an innate ability, but tools and artifacts (the kinds of things that one finds useful to throw or finds useful to manipulate) are themselves products of cultural 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.