Now that scientists can analyze the DNA of any species, they are discovering that many animals that look indistinguishable are actually quite different at the genetic level-different enough to be classified as separate species. That means there may be a lot more biological diversity on Earth than meets the eye.

For example, biologists at the University of California, Berkeley, recently reported the discovery of a new species of Mexican salamander, Lineatriton, that looks identical to another species living several hundred miles away. Only DNA testing can tell them apart.