Who are Nature's brightest brainboxes? How do you measure an animal's IQ? Some species seem to have a greater mental capacity than others, but what's driven them to evolve such intelligence?

We meet the chimps with a better memory than us, cuttlefish that plan ahead, and bees that can count and play football. It's not necessarily the biggest brains that win out but the ones that are engaged most efficiently - to solve problems, remember information and use tools.