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Heritable variation plus differential survival and reproduction changes trait frequencies in populations over generations.
Heritable traits are differences among individuals in a population that can be passed from parents to offspring. When such traits affect an individual’s survival and reproductive success (fitness), natural selection can change their frequencies over generations. If the environment stays similar, advantageous heritable traits tend to become more common; if the environment or niche changes, different traits may be favored, producing microevolution (within-lineage change) and potentially macroevolution (larger-scale diversification), including the origin of new species. Population change is driven by differential reproduction among individuals with different heritable variations. Variation arises from genetic mechanisms such as mutation and recombination, and selection acts on the resulting phenotypes by favoring those that improve reproductive success. Other evolutionary forces also contribute: genetic drift can cause genotypes to change randomly, while different forms of selection (e.g., sexual selection, balancing selection, purifying selection) can either increase, maintain, or remove genetic variation depending on how traits influence fitness across contexts. Over time, changes in heritable traits can lead to reproductive isolation and speciation, especially when gene flow between populations is reduced. As populations diverge, selection can favor incompatible genetic combinations, and selection against hybrids can reinforce isolation. Thus, heritable trait differences—combined with inheritance, variation, and differential reproductive success—provide the core mechanism linking genetics to long-term population change and the emergence of new species.
Heritable variation plus differential survival and reproduction changes trait frequencies in populations over generations.
Natural selection is influenced by fitness and can act in different ways (e.g., ecological vs sexual selection; balancing vs purifying selection).
Population divergence can contribute to reproductive isolation and speciation when gene flow is reduced and incompatible traits spread.
Traits whose genetic basis allows them to be transmitted from parents to offspring.
The differential survival and reproduction of individuals due to differences in heritable traits that affect fitness.
A measure of how much reproductive success an individual’s traits confer relative to others in the population.
Changes in allele or trait frequencies within a population due to selection and other evolutionary forces.
Large-scale evolutionary change over longer timescales, often involving divergence among lineages.
Random changes in allele frequencies due to chance events, which can alter genotypes over time.
Selection driven by competition for mates and mate choice, which can change trait frequencies even if it affects viability.
Selection that maintains genetic variation in a population, often through mechanisms like heterozygote advantage.
Selection that removes deleterious genetic variants, reducing genetic variation over time.
The formation of new species, typically involving reproductive isolation and reduced gene flow between diverging populations.
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