In pop science, nothing is that simple. For instance, there are usually said to be 13 species of finches in the Galapagos, with each species having a highly characteristic beak shape. But scientists have known for many years that these birds almost all inter-breed when circumstances require it. Usually they choose partners with similar beaks & eating habits, but it's not a physically driven, biochemical thing. They are still routinely described as separate species just because of the choices they make.
The world of evolution science is a wonderful world with quite a lot in common with, say, Apple Computer advertising...
Mark W.
The finch beak example is a very poor one. The finch beak sizes are cyclical, they go back and forth from larger to smaller - it's all in their genome. That's something the evolutionists always fail to mention when they use finches as examples of speciation. It's not speciation - it's adaptation as proven by the cyclical nature of the change. They mate together because they are all finches.
Futhermore, a human cannot mate with a non-human and produce offspring. This is certain.