It depends on what you mean by "evolve". In one sense, we've all evolved and changed. For instance, some of us have light skin..some dark. That stuff changes by our geographic location. Those born near the equator need more pigment to protect from the sun's rays. If human being didn't have the ability to change, not only would we all be clones, but we wouldn't have the ability to adapt to our changing environment. It's the same thing with animals. Different animals can take on different characteristics based on what's needed to survive.
That does NOT mean, however, that a species is able to somehow MORPH into another species. A cow is a cow is a cow is a cow. A cat is a cat. A human is a human. There is NO proof of otherwise. No fossils, no biologic explanation as to HOW it might happen...no startling DNA transitions....nothing! To believe in evolution takes a HUGE leap of faith into something that, based on the evidence, seems overwhelmingly impossible.