- A Speciation that is sometimes mistakenly thought to proceed without any geographic separation between gradually diverging populations, with isolation arising mainly from random mate choice within one territory during normal conditions as generally observed
- B Speciation caused by geographic isolation of populations (mountains, rivers, oceans); isolated populations diverge through different selection pressures, genetic drift, and mutation until reproductively isolated; example: Darwin finches on Galapagos Islands
- C Speciation that is sometimes mistakenly thought to occur mainly through sudden chromosome-doubling polyploidy events within a single generation, a mechanism documented mainly in plant lineages rather than animals like finches in typical laboratory settings
- D Speciation that is sometimes mistakenly thought to occur within one single, continuously interbreeding population sharing one largely unbroken gene pool, where gene flow between individuals rarely stops long enough for divergence under usual circumstances
Correct answer: B. Speciation caused by geographic isolation of populations (mountains, rivers, oceans); isolated populations diverge through different selection pressures, genetic drift, and mutation until reproductively isolated; example: Darwin finches on Galapagos Islands
Explanation: Allopatric speciation: geographic barrier divides a population; isolated subpopulations evolve independently (different selection + drift) until they become reproductively incompatible (species). Examples: (1) Darwin finches - colonized different Galapagos islands, diversified into 13+ species; (2) Grand Canyon splitting squirrel populations; (3) Cichlid fish in East African lakes.
Concept context
Origin of life, Darwin's theory, natural selection, speciation, and evidence for evolution.