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🔗 Reinforcement

Reinforcement is selection for increased prezygotic isolation in hybrid zones. When hybrids have low fitness, individuals who avoid mating with the other species are favored. This "Wallace effect" completes speciation.

Low = hybrids do poorly
Species A
Hybrid Zone
Species B
Generation: 0
Prezygotic Isolation: 0.00
Mate Preference A: 0.00
Mate Preference B: 0.00
Hybrid Rate: 0.00
Wallace Effect: Dobzhansky proposed that natural selection against hybrids should favor the evolution of prezygotic isolation. Evidence from Drosophila shows reinforcement can occur in just 5 generations. Sympatric populations show stronger discrimination than allopatric ones.