Against the mainstream of gene-centred evolutionary thinking, a current of biological argument known as "Evo Devo" began relatively recently to emphasise the importance of an organism's development (from conception to maturity) and the two-way street that is the interaction between development and evolution. Biologist Blumberg here offers a fascinating pop exegesis of evo devo, and the title's gambit for attention in a crowded marketplace, which at first appears Barnumesque, turns out to be admirably humane. With famous circus "freaks" as well as beetles and rodents as his examples, Blumberg shows that many unusual formations of human and other bodies - such as missing or extra limbs, double sets of facial features, and so on - are not genetic "mutants" or "monsters", but arise from the very same developmental processes as "normal" bodies do. And this has political implications: an eye-opening late chapter on sexual development in people and numerous animal species decries the fashion for surgical "correction" of "ambiguous" human genitalia shortly after birth. "This is not a system capable of ambiguity," Blumberg writes of mammalian development, "This is a system guaranteed to produce it." We should learn, he concludes, to live with the wide variety of possible physical forms rather than consigning the "monsters" to evolutionary oblivion.