Hopefully avoiding my subject title, I think Joe came closest a few postings back. Still, he didn't recognize the key word here: atrophy. It's much easier for a creature to completely lose physical features that are no longer used than to randomly acquire useful features (that add to positive evolution, in other words a better ability to survive and propagate). A great example is the palmyrus longus (forgive the spelling), a tendon that 90 percent of us no longer use and that the other 10 percent don't even have. It runs from the forearm into the palm, and our nearest relative, the horse, uses it to essentially stand on tip-toes in order to better graze. It's probably related to the wisdom teeth (once used for rumination) and the appendix (probably once a second stomach). All three of these things are no longer needed since most of us humans are no longer grazing animals. So, it's EASY to lose parts we don't need, at least compared to acquiring physical aspects that would make us more successful. A related side note: I know of this tendon because one of mine was transplanted in place of a damaged tendon to my right index finger after a lab accident 30 years ago. Lucky I wasn't one of the more-evolved ten percent! John R.Peterson