- A Speciation that generally and highly requires substantial, long-lasting physical geographic barriers separating the populations involved, such as mountain ranges, wide rivers, or expanses of open ocean between the diverging groups
- B Speciation in the same geographic location without physical isolation; most common mechanism: polyploidy in plants (chromosome doubling creates instant reproductive barrier); also: ecological specialization, sexual selection
- C Sympatric speciation is understood by evolutionary biologists to be largely impossible to actually occur anywhere in nature, despite well-documented cases in cichlid fish and apple maggot flies suggesting otherwise
- D Sympatric speciation is understood to occur mainly within animal populations, having rarely once been observed in plants, even though polyploidy-driven plant speciation is actually one of its best-known examples
Correct answer: B. Speciation in the same geographic location without physical isolation; most common mechanism: polyploidy in plants (chromosome doubling creates instant reproductive barrier); also: ecological specialization, sexual selection
Explanation: Sympatric speciation: new species form within the same geographic area as the parent species. Most documented in plants via polyploidy: allopolyploidy (hybridization + chromosome doubling) creates fertile polyploid that cannot breed with either parent - instant speciation. Example: bread wheat (Triticum aestivum, 6n) formed from hybridization of three diploid grasses. Rare in animals but documented in cichlids.
Concept context
Origin of life, Darwin's theory, natural selection, speciation, and evidence for evolution.