Speciation is not a precise division: overlap between closely related species can occur in areas called hybrid zones. Organisms reproduce with other similar organisms. The fitness of these hybrid offspring can affect the evolutionary path of the two species. Scientists propose two models for the rate of speciation: one model illustrates how a species can change slowly over time; the other model demonstrates how change can occur quickly from a parent generation to a new species. Both models continue to follow the patterns of natural selection.
gradual speciation model
model that shows how species diverge gradually over time in small steps
area where two closely related species continue to interact and reproduce, forming hybrids
model for rapid speciation that can occur when an event causes a small portion of a population to be cut off from the rest of the population
continued speciation divergence between two related species due to low fitness of hybrids between them