A simplified diagram of the process of allopatric speciation with reinforcement after secondary contact. After a geographic barrier arises, two species evolve reproductive isolation. Here, the geographic barrier is removed before complete isolation, whereby the two populations exchange genes. Low fitness hybrids may form, but reinforcement (effectively a process of mate choice discrimination) causes the completion of the speciation process.
<a href="//commons.wikimedia.org/wiki/User:Azcolvin429" title="User:Azcolvin429">Andrew Z. Colvin</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>