Comparative cognition expert Laurie Santos’ research with capuchin monkeys shows that humans and monkeys both fall prey to the same irrational economic tendencies. Capuchins broke off the human line roughly 35 million years ago and share many of our cognitive strategies. “They provide a ‘really great window’ into human behavior of old. In study after study, that window has shown Santos and her collaborators that capuchins indeed repeat many of the economic mistakes once considered unique to mankind — from loss aversion to the endowment effect to certain risk behaviors — suggesting that these irrational tendencies are a long-held, fundamental phenomenon.”