Variation is essential for evolution.

All populations of organisms have individual differences.

These kittens look a lot alike. They have the same kind of fur, and except for one, the same coloring, stripes, and so on. But look closely. Even though they are all from the same litter, there are differences, or variations, among them.

There are also variations that you can't see! These include personality, resistance to disease, and many others.

Siberian kittens © Merja Tolonen, Amante's cattery.