When young animals grow up, they may be similar to their parents but they are never identical. If one animal is able to move faster than another of the same species, it can probably catch more prey and be better fed. It is more likely to be healthy and to attract a mate. Its ability to move fast will probably be passed down to its young, and to their young. Over many generations, the species will evolve (change) to become superb hunters. This process, known as natural selection, was first described by Charles Darwin in the 19th century and explains the way that life on Earth has evolved from the earliest times.