Natural Selection & Population Genetics

Darwin's engine of evolution

Natural selection is the differential survival and reproduction of individuals with heritable traits better suited to their environment. Darwin's four postulates: variation exists in populations; variation is heritable; more offspring are produced than can survive; individuals with favorable traits survive and reproduce more. Hardy-Weinberg equilibrium describes allele frequencies in a non-evolving population (random mating, no selection, no mutation, no migration, large population). Deviations from H-W indicate evolution is occurring. Selection against recessive alleles is slow because heterozygotes 'hide' the allele. Genetic drift (random fluctuations, stronger in small populations) can fix or eliminate alleles regardless of fitness. Bottleneck and founder effects reduce genetic diversity. Over time, selection + isolation → speciation.