Geographic isolation vs. disruptive selection as drivers of new species
0
Generation
0.00
Genetic divergence
0%
Reproductive isolation
—
Stage
Allopatric speciation: A geographic barrier (mountain, river, glacier) splits a population.
Gene flow stops → divergence accumulates via drift and selection.
At secondary contact, they may be reproductively isolated — biological species. Sympatric speciation: Disruptive selection favors two extreme phenotypes in the same habitat.
Assortative mating can amplify divergence without any barrier (e.g., apple maggot fly, cichlid fishes).
Genetic divergence tracked as FST analog across loci.