On this Moment, we discuss why it is so hard to tell cheetahs apart.

If you've ever visited the cat exhibit at the zoo, you probably noticed how difficult it was to tell the cheetahs apart. You may not have known that cheetahs are as genetically similar to each other as identical twins.

Cheetahs have been around for millions of years, but about ten thousand years ago, the climate changed, and only a few members of one species of cheetah managed to survive. This is known as a genetic bottleneck, and it meant that the remaining cheetahs were forced to breed with their relatives.

The cheetah is the oldest of the big cats and has survived the longest. Genetic bottlenecks only lead to extinction if harmful genes make it through and become fixed in the population. The reason cheetahs are endangered is because humans are destroying the cheetah's natural habitat and eliminating its prey.

At the end of the nineteenth century, there were a hundred thousand cheetahs on earth. Now there are around twelve thousand. Evolution just doesn't work that fast. Odds are that if humans would stop interfering with their habitats, cheetahs would continue to survive.