Hybrid speciation might be rare

Why Evolution Is True

Data show that the “normal” mode of speciation—the process in which one lineage divides into two or more species—involves the geographic isolation of populations of a single species. Over time, natural selection (and genetic drift) causes those populations to become more and more genetically different. When the genetic differentiation has gone to the extent that the separate populations evolved features that make them unable to produce fertile hybrids when they come back together in the same area (i.e. regain “sympatry”), then these populations have become separate species. They are now groups on distinct evolutionary trajectories, and their inability to exchange genes because of the evolved “reproductive isolating barriers” between them (e.g., behavioral differences in mating, preferences for different host plants or microhabitats, different times of mating, different pheromones, or the sterility or inviability of hybrids), is what makes nature “lumpy” rather than a continuum. The lumpiness of nature—the fact that, in a single…

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