natural selection
process by which there is an inherent variation in population of organisms, variant best suited for growth and reproduction in a given environment contribute disproportionately to future generations (an evolutionary mechanisms that leads to adaptation)
natural selection (book)
depends on differential success-in terms of surviving and reproducing-in variants
species
consists of individuals that can exchange genetic material through interbreeding (group of species capable, through reproduction, of sharing alleles with one other)
populations
interbreeding groups of organisms of the same species living in the same geographic area