Pre-Darwinian theories
Several philosophers of the classical era, including Empedocles and his intellectual successor, the Roman poet Lucretius, expressed the idea … See more

Heritable variation, differential reproduction
Natural variation occurs among the individuals of any population of organisms. Some differences … See more

Natural selection is seen in action in the development of antibiotic resistance in microorganisms. Since the discovery of penicillin in 1928, antibiotics have been used to fight bacterial diseases. The widespread misuse of antibiotics has selected for microbial … 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, … See more

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