evolution has been happening since life started on earth and is happening now. evolution is caused mostly by natural selection. living things are not identical to each other. even living things of the same species look, move, and behave differently to some extent. some differences make it easier for living things to survive and reproduce. differences may make it easier to find food, hide from danger, or give birth to offspring which survive. the offspring have some of the things which made it easier for their parents to have them. over time, these differences continue, and living things change enough to become new species.