Which is the fastest animal on land?

A cheetah reaches something between 100 and 120 kilometres an hour and gets there in about three seconds, which is quicker off the line than most sports cars. Almost everything about the animal has been given over to that: an oversized heart and lungs, wide nasal passages to get air in, a spine that flexes like a bow to lengthen the stride, a long tail used as a counterweight in turns, and claws that stay partly out as running spikes rather than retracting like other cats'.

The cost is that it cannot keep it up. A cheetah overheats within roughly half a minute and has to stop, and then needs a long recovery before it can even begin eating - during which lions and hyenas frequently take the kill. A large fraction of successful hunts feed something else.

There is a hidden fragility as well. Cheetahs have startlingly little genetic diversity, the legacy of a population crash perhaps 10,000 years ago; skin grafted between two unrelated cheetahs is accepted by the recipient's immune system as its own, which is a thing you would otherwise only see between identical twins. It leaves the species unusually exposed to any single disease.