Speciies? you gotta be kidding.

[Rduke55]

[ QUOTE ]
[ QUOTE ]
Just to be clear, you agree that if we took a census of all the sexually reproducing multicelled organisms on the planet (species for other organisms is a whole other, ugly question) most of them could be classified into distinct, interbreeding groups that are infertile with other groups?

[/ QUOTE ]

We could do that with "has more than 50% brown pigment" or "more than 6 legs". Not trivializing the usefulness of the interbreeding constraint, but it is arbitrary nonetheless. I'm not sure why that fact is bothersome. I'd be interested in your expansion on that reasoning.

luckyme

[/ QUOTE ]

Because that's the simple distinction that can be made that has massive influences on evolution. The other examples don't. Once you put up that barrier to gene flow then each population travels a unique path.