Adaptation is a characteristic of an organism that makes it better able to survive and reproduce in its environment. No two organisms of the same species are exactly alike. Every trait, such as size, color, and personality, shows some variation. Additionally, in nature, organisms produce more offspring than can survive. The offspring most likely to survive and reproduce are those with adaptations best suited to the environment. Offspring with variations less suited to the environment do not compete as successfully for food, water, and other necessities. This process of competition, by which those best adapted are most likely to survive and reproduce is called natural selection (see Evolution).