Natural selection is treated as the primary—and by some scientists the sole—mechanism producing evolutionary change. In essence it involves the process whereby some aspect of an organism’s environment (either climate, competition, predation, or parasitism) inter-acts with one or more traits of the organism, such that the survival or reproduction of that organism is enhanced (or diminished) relative to organisms that lack those traits. Natural selection is intimately tied to the phenomenon of adaptation: adaptations are honed by natural selection; over time the proportion of organisms with these adaptations will increase in a population because of natural selection.
Natural selection is associated with the idea that nature is red in tooth and claw, the implication being that there is a fierce competitive struggle among all organisms, with natural selection weeding out those less fit organisms while favoring those that are more fit.
