A tale of scrotality and other pressing mammalian concerns.
A neurobiologist by training, science writer Drew relates that some time ago, he got it in his head that readers might enjoy “a lengthy discussion of the natural history of scrotums,” and all that remained was to find an editor who agreed with him. After some rejections, he did, first for a magazine and then for this book, which indeed includes, among other things, a lengthy discussion of the natural history of scrotums—perhaps too lengthy. The author explores other mammalian matters, of course, among them the fact that there are not so many kinds of mammals in the world once one discounts bats and rodents: by his reckoning, 1,687 species. As Drew writes, “rats, mice, voles, squirrels, chipmunks, gerbils, guinea pigs and their kin accout for just over 40 percent of all mammals.” And, the subject being mammals, mammaries naturally enter into the narrative, and the author connects their evolution to the triad of apocrine gland, sebaceous gland, and hair follicle. Readers may be delighted to learn, finally, that the egg indeed preceded the chicken, although “biologists are at a bit of a loss as to why the egg evolved.” Drew’s account is doggedly Darwinian, allowing for modern interpretations of things like clades and radiative adaptations, and his argument often proceeds from technical fine points. “Might the evolution of a key trait,” he asks, “have given therapsids, say, an edge over pelycosaurs? Did a uniquely mammalian character allow mammals to succeed cynodonts?” The answer is an elusive yes and no, but the ability to entertain contending possibilities is another thing that makes us human—i.e., mammalian with a few more folds of the cortex, descended testicles, a constant body temperature, and such.
A solid and demanding account, one best read after some grounding in current evolutionary and biological theories.