Charles Darwin considered them extraneous, but this witty book sheds moderns scientific light on the Darwin Six --appendix, tailbone, "third eyelid," wisdom teeth, external ear muscles, body hair -- once considered useless, now known to be both valuable and interesting, plus a chapter on the true "dispensables," parts with which we can indeed dispense. Along the way, best-selling author Rinzler weaves in Darwin's brilliant and ground-breaking theories of evolution and shares insights into what the human body may look like millennia from now.