I was talking with a friend about the Polio vaccine, when he said to me that evolutionary biology has a major problem because you cannot do experiments in it because there are too many variables. His example was, if you have three bears in a snowy environment, one black bear, one brown bear, and one white bear, you cannot do tell which one will live the longest because there are too many variables. The black bear could be stronger than the white bear and brown bear, etc. Sure, the white bear could blend in into the snowy environment, but that's not necessarily an advantage to it's survival because it could just as easily be killed by something else. His other example was with opposed thumbs. Is it possible for the thumb to become too opposed, so opposed that it no longer is a benefit to survival or to the specimen the thumb inhabits, and at what point did thumbs become a survival mechanism? It got me thinking.