Pre-Darwinian theories
Several philosophers of the classical era, including Empedocles and his intellectual successor, the See more

Heritable variation, differential reproduction
Natural variation occurs among the individuals of any population of organisms. Some differences may improve an individual's chances of surviving and reproducing such … See more

Natural selection is seen in action in the development of antibiotic resistance in microorganisms. Since the discovery of penicillin in … See more

Genotype and phenotype
Natural selection acts on an organism's phenotype, or physical characteristics. Phenotype is … See more

The term natural selection is most often defined to operate on heritable traits, because these directly participate in evolution. However, natural selection is "blind" in the sense … See more

Natural selection can act on any heritable phenotypic trait, and selective pressure can be produced by any aspect of the environment, including sexual selection and See more

A prerequisite for natural selection to result in adaptive evolution, novel traits and speciation is the presence of heritable genetic variation … See more