The critical transition for hominids was the dawn of imitation, perhaps two and a half million years ago, before the advent of stone tools and expanding brains.

• 在演化过程中，人科动物最关键的转变就是变得善于模仿，那大概发生在250万年之前，那时人还没有发明石器，脑子还没扩张（与现生黑猩猩的脑子一样大）。