Keeping wild animals contained and available for human enjoyment isn't a modern phenomenon.

There's evidence that rulers in ancient Egypt had what they called menageries and a Chinese emperor in the 11th century B.C.E. cultivated a "garden of intelligence." The conditions of those places were, as you might imagine, generally pretty bad: wild animals were captured from their native environments and cared for by people with little to no awareness of their typical diets and behaviors.

And conditions in zoos more or less stayed this bleak for a long time.

Things started to shift in the late 1800s, with the introduction of positive reinforcement, a philosophy often attributed to a guy named Carl Hagenbeck.

He was a German merchant who supplied animals to zoos, circuses and such.

While Hagenbeck engaged in some questionable practices, he eventually took up the cause of humane animal treatment.

And this was totally radical at the time.

Instead of forcing an animal to do something, which often involves physical or emotional abuse, you coax them into the behavior with a reward.

Positive reinforcement means that, ultimately, the animal can do what it wants.

If that behavior aligns with what the trainer wants, then the animal gets a treat or some other sort of reward.