Okay, I have a question already. The following -
A few years later, Dobzhansky defined a species as
"... that stage of evolutionary progress at which the once actually or potentially interbreeding array of forms becomes segregated into two or more separate arrays which are physiologically incapable of interbreeding." (Dobzhansky 1937)
What is an example of this? What was able to interbreed but at a point was no longer able to interbreed?
Thanks. I don't want to bother you with this but I'm really trying to understand. I'm sure you're busy today and I don't want to waste your time, but you help is appreciated.