What's the easiest way to tell species apart? Check their genitals. Researching private parts was long considered taboo, but scientists are now beginning to understand that the wild diversity of sex organs across species can tell us a lot about evolution. Nature's Nether Regions joyfully demonstrates that the more we learn about the multiform private parts of animals, the more we understand our own unique place in the great diversity of life.
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ABOUT THE AUTHOR . . . yes and his heart was going like mad and yes I said yes I will Yes. -James Joyce, Ulysses Preliminaries Not too long ago, the Netherlands Natural History Museum was housed in a lofty, cavernous building in the historical center of Leiden. Generations of biology students took their zoology classes there, in its two-tier lecture theater over the monumental staircase. During the less captivating parts on crustacean leg structure or mollusk shell dentition, their gaze would have wandered off to the two features that made this lecture room unforgettable. First, its abundant display of antlers of deer, antelope, and other hoofed animals, hundreds of them, suspended from the walls. Second, the huge painting from 1606 of a beached sperm whale that hung over the lectern. On an otherwise nondescript Dutch beach lies the Leviathan, its beak agape, its limp tongue touching the sand. A smattering of well-dressed seventeenth-century Dutchmen stand around the beast. Prominently located, and closest to the dead whale, stand a gentleman and his lady. With a lewd smile, face turned toward his companion, the gentleman points at the two-meter-long penis of the whale that sticks out obscenely from the corpse. Centuries of smoke-tanned varnish cannot conceal the look of bewilderment in her eyes. These few square feet of canvas, strategically placed in the painting's golden ratio, exemplify two things. First, the unassailable fact (supported by millennia of bathroom graffiti, centuries of suggestive postcards, and decades of Internet images) that humans find genitals endlessly fascinating. Their own, but by extension those of other creatures, too. The amazing diversity in shape, size, and function of the reproductive organs of animals has been an eternal source of wonder, making bestsellers of the 1953 book The Sex Life of Wild Animals, the 1980s classroom wall poster Penises of the Animal Kingdom (over twenty thousand copies sold), and the Sundance Channel series Green Porno- short films starring a sanguine Isabella Rossellini enacting the copulation of various animals. The second point that may be underscored with this seventeenth-century sperm whale penis is the curious observation that the public fascination with genitalia was, until very recently at least, not matched by equally intensive scientific inquiry. The lofty offices down the corridor from this lecture theater housed scores of biologists quietly cataloging the world's biodiversity. In good classificatory tradition, they would painstakingly draw, measure, photograph, and describe the minutiae of the genitals and distinguishing features of the reproductive organs of any new insect, spider, or millipede they would discover-and yet never stop to wonder how these private parts evolved. We really have Darwin to blame for this. In his next-greatest book, The Descent of Man, and Selection in Relation to Sex (1871), Darwin explains how secondary sexual characteristics-like colorful bird plumage, the prongs on beetles' heads, and the antlers of deer-have been shaped not by natural selection (adaptation to the environment) but by sexual selection: adaptation to the preferences of the other sex. He denies the primary sexual characteristics entry to his theory by categorically stating that sexual selection is not concerned with the genitalia or primary sexual organs-which, after all, are merely functional, not fanciful. So the diversity of all those antlers on the walls of the museum lecture room had been a tradition of evolutionary biology since Darwin, but investigating the evolution of the business end of things-of which the centerpiece of that seventeenth-century painting is just one prominent example-hadn't. It took until 1979 for evolutionary biology to start paying attention to genitalia. In that year, Jonathan Waage, an entomologist from Brown University, pub