Playing by the same rules reduces the differences between humans, chimps and monkeys

You’ve been asked to compete against some of your friends in a game of skill, but you realise something is amiss. They’ve been given precise instructions and details about the game’s mechanics. You’ve been given a couple of pieces and left to figure things out on your own. On this uneven playing field, no one could fairly compare your performance with that of your friends. This seems obvious, but it’s a problem that plagues a lot of research into the behaviour of humans and other animals. Scientists will often test monkeys and apes with tweaked versions of psychological games that were originally designed to test humans. The goal is simple: understand the similarities and differences between our mental abilities and those of our closest relatives. But these comparisons are tricky. Frans de Waal, who studies the behaviour of apes and monkeys, says, “Humans are tested by their own species and ...