Orang-utans and corvidae such as the rook have already met the challenge with 100% success. But how would chimpanzees, gorillas and human children fare against the challenge of a treat placed in the bottom of a tube, requiring the addition of water (or displacing of water by stones) to bring it to the top?

Gorillas displayed the worst response, with not a single one able to complete the task. Human children were slightly better, with 8% of four-year-olds, 42% of six-year-olds and 58% of eight-year-olds able to obtain the treat. Most interesting was the response of the chimpanzees. While they were only better than humans of two years old - 33% worked out they needed to spit water into the tube to gain their peanut - one individual showed particular ingenuity in solving the problem. He initially responded the expected way, but seemed to become frustrated in trying to direct the water into the tube. The chimpanzee subsequently realised that peeing into it would have the same - but more rapid - effect. The fact that the peanut was sodden with urine didn’t deter him from then claiming his prize. Kudos.

See the link for a video of a chimpanzee solving the problem in the standard manner!