Thus, the start-up problem means that the conditions under which there's enough cumulative culture to begin driving genetic evolution are rare, because, early on, there wouldn't have been enough of an accumulation to pay the costs of bigger brains. And if there had been, the most adaptive investment would be in improved individual learning, not better social learning or eventually cultural learning. So in order for natural selection to favor improved social learning, there has to be a lot of cultural stuff to learn, but if you don't have much social learning, there's unlikely to be much of an accumulation out there to tap.

— Joseph Henrich, The Secret of Our Success (2016)