Natural selection
Evolutionary psychologists consider Charles Darwin's theory of natural selection to be important to an understanding of psychology. Natural selection occurs because individual organisms who are genetically better suited to the current environment leave more descendants, and their genes spread through the population, thus explaining why organisms fit their environments so closely. This process is slow and cumulative, with new traits layered over older traits. The advantages created by natural selection are known as adaptations. Evolutionary psychologists say that animals, just as they evolve physical adaptations, evolve psychological adaptations.