Speciation

Speciation is the evolutionary process by which populations diverge into distinct species. It occurs when barriers to gene flow allow genetic differences to accumulate.

Reproductive isolation: Restrictions on gene exchange that prevent populations from producing fertile offspring together. It is the central condition that keeps diverging populations genetically separate.
Gene flow: The transfer of alleles between populations through migration and reproduction. Gene flow tends to reduce differences that could otherwise contribute to speciation.
Biological species concept: A species concept that defines species by actual or potential interbreeding and reproductive isolation. It connects speciation directly to the evolution of barriers to interbreeding.
Darwin's finches: A group of Galápagos songbird species whose beak forms and diets vary among islands and habitats. Their diversification illustrates how ecological differences and restricted gene flow can interact.
Allopatric speciation: Speciation that follows geographic separation of populations. A physical barrier can interrupt gene flow and set divergence in motion.
Genetic drift: Random changes in allele frequencies caused by finite population size. Drift can drive populations apart, especially after a small group becomes isolated.
Phylogenetic species concept: A species concept that identifies the smallest diagnosable lineage on a phylogenetic tree. It can recognize distinct lineages even when reproductive isolation is unknown.
African cichlids: A diverse group of freshwater fishes that underwent extensive evolutionary radiations in African lakes. Their rapid diversification offers cases of ecological and sexual divergence within connected waters.
Sympatric speciation: Speciation within a shared geographic area, without a physical barrier separating populations. It shows how divergence can proceed despite populations living alongside each other.
Natural selection: A change in inherited traits across generations caused by differences in survival or reproduction. Different environments can favor divergent adaptations in separated populations.

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