To test the premise, researchers designed a tray that was too heavy for a single monkey to pull into the cage.

FORBES: Primate Economics

Like normal males, the mutant mice urinated in various spots around their cage (unlike females, who create a single latrine).

ECONOMIST: Behaviour of the sexes

It holds about fourteen thousand worker bees and a single queen, who is housed, along with a few devoted attendants, in a tiny cage.

NEWYORKER: Stung

This time a single rook was presented with the same tray-string set-up, while its pair waited in a neighbouring cage linked by a one-way flap.

BBC: Rooks team up to solve problems