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What kinds of isolation can lead to the formation of a new species?

According to the biological species concept, populations are different species if gene flow between them is prevented by biological differences, known as reproductive barriers. If populations exchange genes they are conspecific, i.e. belong to the species, even if they differ greatly in morphology. If they are reproductively isolated, they are different species even if they are indistinguishable phenotypically. Therefore speciation arises from the evolution of biological barriers to gene flow (Futuyma, 1998).

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