Over a long period of time, differences add up and lead to the formation of new species.

These are all cats. They are all related to each other, but they look very different. In fact, there is a large variety of cats.

White Bengal tiger by Donovan Gutierrez, courtesy of HDW Enterprises, Inc., www.hdw-inc.com; Jaguar, sand cat, and margay © Nancy Vandermey, www.cathouse-fcc.org; African Lions by Gerald and Buff Corsi, © 2001 California Academy of Sciences.