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My, layperson, understanding is that if they can interbreed and produce fertile offspring, then they are the same species. So two types of fly that can't inter-

My, layperson, understanding is that if they can interbreed and produce fertile offspring, then they are the same species. So two types of fly that can't inter-breed would be classified differently. I don't think that's quite accurate (for example, ligers are capable of reproduction, though they would never be born 'naturally' due to the vast geographical separation of lions and tigers in the wild) but it might point you in the right direction.

mdiep 15y ago
For a long time, that was also my impression. But it's wrong. Mostly. It turns out that there isn't a single definition for the word species—there are multiple definitions that lead to different results. Reading through the Wikipedia article about species will give you a sense of the different definitions. http://en.wikipedia.org/wiki/Species http://en.wikipedia.org/wiki/Species If you use the Biological/Isolation species definition, I think you could argue that humans are or were multiple species. (Please, someone correct me if I'm wrong on this.)