In The New Republic, Ben Cair asks What's a Species Anyway? Good question!
The idea of a species may be fundamental to biology; but science offers no precise definition of what a species actually is. Anyone can recognize a black bear and a cardinal as distinct animals, but what about two minnows scooped from separate ponds? For centuries, taxonomists delineated species based on morphology, ecology, and behavior, but there was never any standard method to their classifications. Some taxonomists lumped different populations together based on general similarities, while others split them apart based on minor variances. A taxonomist named C. Hart Merriam working in the United States in the 1880s insisted that there were at least 86 species of grizzly bear in the collection of the National Museum of Natural History in Washington, D.C.Yep.
As genetic testing has become more common, biologists have found increasing evidence of hybridization among distinct species. Bobcat and lynx are hybridizing in Canada. The clymene dolphin is entirely a hybrid of two other dolphin species. Scientists have theorized that climate change may be the cause of some hybridization, as animals migrate outside of their traditional ranges and encounter new species. The “pizzly bear,” for example, is a cross between a polar bear and a grizzly bear. But the polar bear and grizzly bear genomes show that the two species have exchanged genes throughout history. So have grizzly bears and black bears. Even human beings aren’t quite as distinct as we once thought. The genomes of European and East Asian peoples contain genetic material from long-extinct Neanderthals, indicating that hybridization has played a role in our own development as Homo sapiens.
As I noted some years back, and reposted this morning, Darwin drives a hybrid animal, and what people call an animal, or what they say about DNA, matters very little. "Species" is a human construct. Watch the animal. They're the experts, and they will tell you. The fact that two animals can cross under extraordinary circumstances does not mean they are not two different species. The real question is what happens under normal circumstances. What then?