At my supermarket, I can buy strawberries in winter and pears in summer. Every fruit is available all year round, and the shelves are always stocked. Thanks to this constant glut, it’s easy to forget what a patchy and fleeting resource fruit can be. Even in a tropical rainforest—a world of supposed abundance—animals might have to walk for miles to find the one tree in every 500 that has ripe fruit on it. That tree might only carry ripe fruit for a few weeks, and any juicy baubles would be rotten or eaten within days.

So fruit-eating animals like chimpanzees need good memories and flexible brains. They need to remember where the best trees are and when they are likely to