Evolution has been happening since life started on Earth and is happening now. Evolution happens mostly by natural selection. Living things are all different from each other. Even living things of the same species look, move, and behave differently. Some differences make it easier for living things to survive and have babies. Differences may make it easier to find food, hide from danger, or have babies. The babies keep some of the differences that made it easier for their parents to have them. Over time, these differences get bigger and living things change enough to be a new species. 