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

Genotype and phenotype
Natural selection acts on an organism's phenotype, or physical characteristics. Phenotype is determined by an organism's genetic make-up … 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 … See more