Is a change over time in the frequency with which particular genes - and the characteristics they produce. Characteristics that increase the likelihood of survival and ability to reproduce within a particular. Natural selection: environment will be more likely to be preserved in the population. Darwin knew that there was an overproduction problem: more individuals are born than survive to reproduce. He inferred that: competition among individuals in a population; only some offspring survive to reproduce. The products of natural selection are called adaptations adaptations reproductive ability. Allow organisms to meet recurring environmental challenges to their survival thereby increasing in evolutionary psychology: seeks to understand how behavioural abilities and tendencies have evolved over the course of millions of years in response to environmental demands. Have we evolved patterns for choosing a mate and reearing our children. Time effort energy risk, associated with caring successfully for each offspring. Humans invest a great deal in small # of offspring.