In response to your question about DNA, the answer is: sometimes it is neccessary.
Before this technology existed, people relied on morphology and to a lesser extent other traits like behavior to classify different species. The problem is there are sometimes few if any characters that allow robust classification among closely related species. But DNA provides an almost endless number of characters, even at the level of individuals. It boils down to whether there is enough variation in non-DNA data.

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Rush Limbaugh IS A BIG FAT IDIOT
-Al Franken

And I agree!