This book provides some helpful background and insight into what's being called evo-devo, showing the interplay between 'traditional' genetic sources of evolution, and the developmental process as an embryo or fetus grows into a creature. Many kinds of 'freak' or monster are not due to genetic mutations, but different developmental environments causing the correct developmental processes to create unexpected results. There's no mutation that makes a four legged chicken - the mechanism for making a pair of legs gets turned on twice. A case with humans provides a lot of insight. When your face develops, there's an eye patch that develops. Normally, the patch divides into two, and your protonose, which starts forming high up on your forehead, then slips down between the eyes to take up its normal position. Well, if the eyepatch doesn't separate, then the nose can't make it through. Thus, cyclopia is associated with having a sorta proboscis on the forehead.
There was also some interesting discussion of how experience was also an important ingredient to the mix of genes and development. If you're Johnny Eck, you move quite gracefully. It seems absurd to suppose that there is some inborn instinct to cover his case. His fluid motion looks natural and like it is the result of an organic whole. But this behavior is a result of a particular body interacting with the underlying physics of motion. For a less freakish case, the jerboa starts its life crawling, and then walking on all fours, but as the hindlegs continue to grow, quadrupedal motion becomes more and more awkward, and the final bipedal gait is favored, not necessarily by instinct, but through the interaction of physics, and experience, on the developing shape of the organism.
There's a lengthy discussion of intersex conditions in people, and some of the even more extreme sexual forms and strategies of animals. I knew some lady hyenas have, um, impressive clitorises. I did not realize they gave birth through them (and likewise screw through them).
As a biological ignoramus, I found it a great introduction to these ideas, although occaisionally a little dry and overdetailed.