Why were zebras never domesticated?

Zebras were never completely domesticated, and the best-known explanation says that taming a species is like a long checklist: one failed item is enough. Jared Diamond popularised this in his 1997 book Guns, Germs and Steel, borrowing the Anna Karenina principle. The idea is that success in a complex endeavour needs every key factor to be present, so there are many ways to fail. Applied to animals, a species is domesticated not because of one special trait, but because it has none of a long list of bad ones.

On Diamond's list are growth rate, since an animal has to grow fast enough to be worth keeping (elephant farmers would wait perhaps twelve years for adult size), and breeding in captivity. There is the tendency to panic, since an animal that bolts when frightened is a poor candidate, and a species that freezes or stays with the herd is a good one. And there is social structure: a species with a strong, well-defined hierarchy is more likely to be domesticated.

In his book the zebra is the special case. Local cultures and Europeans alike saw it as extremely valuable and useful, and yet it proved impossible to tame. One suggestion is that evolving under pressure from Africa's many large predators, including early humans, made zebras more aggressive.

It is not that zebras cannot be handled. In the late 19th century the zoologist Walter Rothschild trained zebras to draw a carriage in England and drove it to Buckingham Palace to prove it could be done. But training a few animals is not domestication, and zebras have never been completely domesticated, unlike horses and donkeys. Diamond's wider argument has critics, so it is best read as a theory rather than a settled answer.