Menno Schilthuizen - Natures Nether Regions: What the Sex Lives of Bugs, Birds, and Beasts Tell Us About Evolution, Biodiversity, and Ourselves

ALSO BY MENNO SCHILTHUIZEN

Frogs, Flies, and Dandelions: The Making of Species

The Loom of Life: Unravelling Ecosystems

VIKING

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First published by Viking Penguin, a member of Penguin Group (USA) LLC, 2014

Copyright 2014 by Menno Schilthuizen

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Illustrations by Jaap Vermeulen. Copyright 2014 by Menno Schilthuizen.

LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA

Schilthuizen, Menno.

Natures nether regions : what the sex lives of bugs, birds, and beasts tell us about evolution, biodiversity, and ourselves / Menno Schilthuizen.

pages cm

Includes bibliographical references and index.

ISBN 978-1-101-60810-4

1. Generative organsEvolution. 2. Sexual behavior in animalsEvolution. I. Title.

QL876.S35 2014

573.6dc23

2013047833

Version_1

... 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 paintings 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 Pornoshort 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 worlds 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 discoverand 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 characteristicslike colorful bird plumage, the prongs on beetles heads, and the antlers of deerhave 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 organswhich, 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 thingsof which the centerpiece of that seventeenth-century painting is just one prominent examplehadnt.

It took until 1979 for evolutionary biology to start paying attention to genitalia. In that year, Jonathan Waage, an entomologist from Brown University, published a short paper in Science on the damselfly penis. He demonstrated that this minuscule penis carried a miniature spoon that, during mating, cleaned out the females vagina, scooping out any remaining sperm from previous males. It was an eye-opener as well as a sperm-scooper. For the first time, here was proof that animal genitals are not just mundane sperm-depositing and sperm-receiving organs, but are sites where a sexual selection of sorts goes on. After all, during damselfly evolution, males with the best sperm-scoopers had left more descendants.

The time was ripe for this paper. When I interviewed Waage about those early days, he recalled how, in the years leading up to his sperm-scooper discovery, he had been influenced by the quiet revolution that biology faculties worldwide were undergoing at the timea sea change brought about by George C. Williamss book Adaptation and Natural Selection and by Richard Dawkinss popularization of it, The Selfish Gene. People began to do away with the false notion that evolution works for the good of the species (an outdated concept, echoes of which can be heard even today in nature documentaries). Instead, they began viewing evolution correctly, as the effect of a kind of reproductive selfishness, in which it is all about the success of an individual in carrying its genes into the next generation. Evolution does not care about the species. And if a sperm-scooper would scupper the chances of competing males, then that is what evolution would favor. Waage was one of the first scientists to start asking the questions that mattered for how evolution works. And since evolution is all about reproduction, no wonder Waage and other modern biologists would sooner or later find themselves closely inspecting genitals.

In that same revolutionary era, other young biologists began asking similar questions. One of them was a certain undergraduate biology student who in the 1960s was earning some extra cash with menial tasks in the depot of Harvard Universitys Museum of Comparative Zoology. His job was to top up the alcohol in jars with pickled animals and to organize unsorted spider specimens. Picking up spider identification guides, the student began wondering why spider species are so often distinguished by the way their genitals are formed. Asking around in the museum, he was told that that is just the way it is. The genitals of different species of animals, be they spiders, spittlebugs, or Spanish fly, are often widely different, even if the species are one anothers close relatives and look identical on the outside. Probably, his seniors told him, the genetic differences also accidentally affect the shape of the genitals. Very useful if you want to identify spiders, but probably quite meaningless biologically. The student, unconvinced but not in a position to argue, shelved the question in the back of his mind, graduated, and went on to become a productive and successful tropical biologist at the Smithsonian Institutions Tropical Research Institute in Panama.