Does introgression require interspecific hybrids to be fertile? How is this possible? Wikipedia says that Introgression, also known as introgressive hybridization, in genetics is the movement of a gene (gene flow) from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Does this mean that the interspecific hybrid is fertile? But is it possible, that an interspecific hybrid is fertile?

> Does this mean that the interspecific hybrid is fertile?

Yes

> But is it possible, that an interspecific hybrid is fertile?

Yes

You might be confused by the idea that by definition two individuals from different species should not be able to interbreed. If so, then you should have a look at How could humans have interbred with Neanderthals if we're a different species?.