There are many scientists who study the mental abilities of animals. As intelligent animals ourselves, we’re keen to learn whether other species share our skills, and how our vaunted smarts evolved. We see study after study about whether chimpanzees care about fairness, whether pigeons outsmart humans at a classic maths problem, whether cuttlefish can remember where, what and when, or whether (and how) parrots and crows use tools,

But animals are hard to work with. You need to design tests that objectively assess their mental skills without raising the spectre of anthropomorphism, and you need to carefully train them to perform those tests. These difficulties mean that researchers mostly resort to small experiments with just one species, often