Evolution's Rainbow. Joan Roughgarden

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СКАЧАТЬ masculinized genitals of female hyenas are an example of what I call a social-inclusionary trait, which allows a female hyena access to resources needed for reproduction and survival. If a female were not to participate in social interactions using her penis for signaling, she would not be able to function in hyena society and presumably would either die or fail to breed.

      It has been suggested that the enlarged clitoris is a side effect of high testosterone levels in female spotted hyenas.²⁷ Social life among female spotted hyenas involves lots of aggression, possibly caused by elevated blood testosterone. This testosterone might produce incidental “excess” masculinization during development. I don’t buy this theory. Aggressiveness doesn’t require testosterone. We’re not talking about a slightly larger clitoris, but a full-fledged replica of male genital anatomy, complete with scrotal sacs and fat bodies resembling testicles. This structure can’t develop from a few extra splashes of testosterone in the blood. I believe this case demonstrates that mammalian genitals have a symbolic function. In fact, displaying genitals is a mammal thing. Fish, frogs, lizards, snakes, and birds rarely have external genitals pigmented with bright colors to wave around at one another. Mammals do.

      Penises can be seen in various female primates, such as bush babies, nocturnal squirrel-like primates from central Africa. Among the dozen or so known species of bush babies, all the females have a penis—that is, a long pendulous clitoris with a urethra extending through the tip so that they can pee through it.²⁸ The males have a bone in their penis called a baculum. Copulation is unusually slow in these primates, lasting one to two hours.²⁹

      Field guides to spider monkeys of South America refer to a pendulous and erectile clitoris long enough to be mistaken for a penis.³⁰ Over half a dozen species of these monkeys exist, named for their spectacular ability to hang from prehensile tails and move around the treetops using their hands, feet, and tails as though they were five-legged creatures. Because the clitoris looks like a penis, the presence of a scrotum is used as a field mark to indicate whether the subject is male. Scent-marking glands may also be present on the clitoris of spider monkeys.

      In woolly monkeys, close relatives of the spider monkeys, the clitoris is actually longer than the penis.³¹ In still another close relative, the muriqui, nipples are located along the sides, under the arms. Thus, even in primates, a gendered body can be assembled on a vertebrate chassis in many ways.

      One reason the public presentation of genitals is such an emotionally charged issue for us humans is that primates use their genitals in displays even more than other mammals do. Picture books about animals often feature baboons called drills and mandrills, showing the male’s colorful snout. A full-body photo, rather than just a head shot, would reveal that the color extends to the genitals. Both males and females have bright red genitals. The male displays a crimson-red penis riding astride a snow-white scrotum, and an estrous female displays large red bulbous swellings surrounding her vagina. The drills provocatively present these areas to one another’s view.³² Our own practice of covering the genitals with clothes except in particular evocative situations bespeaks the symbolic power of genital design and decoration for us too. Medicine’s peculiar history of assigning gender based on genital anatomy can undoubtedly be traced to our primate dependence on genitals as symbols.

      How about feminized male genitals? Spotted hyenas, bush babies, and spider monkeys offer cases of masculinized female genitals. What about the reverse? The genitals of male dolphins and whales apparently represent a different type of intersex. For the purposes of hydrodynamic streamlining, male dolphins and whales don’t have external genitals. Instead, paired testes are located within the body cavity. The penis is cradled inside a “genital slit” and covered by flaps unless it is erect. Male cetaceans have no scrotum.

      What would be the easiest way to develop this genital architecture for males, using mammalian body parts and a vertebrate chassis? Some of the steps ordinarily taken by terrestrial mammalian males when their genitals are developing could simply be omitted. On land, a male mammal’s testes descend from the body cavity into the scrotum, whereupon they become testicles. The scrotum is derived by fusing the tissues that in females become the labia covering the vagina and clitoris. By not bothering to fuse the labial tissue into a scrotum and leaving the testes in the abdominal cavity, a developing male dolphin or whale keeps his testes protected, using the labial tissues as protective flaps. The clitoris continues to develop into a penis, as the urethra becomes included along its axis. If these steps took place on land, a mammalian male would be classified as intersexed. Thus, we might speculate that male dolphins and whales have achieved their genital architecture by making a norm out of what would otherwise be considered an exceptional intersex morphology.

      Both genital and gonadal intersexes are documented in wild cetaceans. The striped dolphin (Stenella coeruleoalba) has some individuals who display external female genitals along with testes and internal male plumbing. The bowhead whale (Balaena mysticetus) has individuals with female external genitalia and mammary glands combined with male chromosomes, testes, and male internal plumbing. A fin whale (Balaenoptera physalus) has been described with both male and female reproductive organs, including uterus, vagina, elongated clitoris, and testes. A beluga whale (Delphinapterus leucas) in the St. Lawrence seaway had male external genitals combined with a complete set of two ovaries and two testes.³³

      Although a recent report on intersexes among cetaceans raises the specter of pollution causing genital deformity, the early reports on intersexes predate dangerous levels of pollution. Perhaps cetaceans are on their evolutionary way to the state that hermaphroditic fish have already attained.

      The examples so far have focused on intersexed genital plumbing. What about intersexed gonads? In four species of burrowing mammals from Europe called old world moles, males have testes typical of other mammals, whereas all the females have ovotestes, containing both ovarian and testicular tissue. The females make eggs in the ovarian part of their ovotestes, whereas the testicular portion has no sperm, although the testicular portion does actively secrete hormones. These species come close to being hermaphroditic.³⁴

      Thus a number of mammalian species have recombined genital plumbing and gonads in surprising and successful ways. More generally, we see that among vertebrates, from fish through mammals, the binary distinction in gamete size does not generally extend to the entire body. Many body plans include production of both sizes of gamete at different times or the same time, as well as various genital sculptures and mixtures of genital plumbing—all as a way of serving social functions important in the society of the species.

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      Sex Roles

      Even species thought of as typical, with one gender per sex and individuals who maintain a single sex throughout life, often have gender roles quite different from the traditional template. Indeed, in some species, males (apart from making sperm) look and behave much as females do in other species, and females (apart from making eggs) look and behave much as males do in other species. If these species could express their thoughts about us, they would describe our gender distinctions as reversed.

      BODY SIZES REVERSED

      Anglerfish are deep-sea fish who have what looks like a tiny fishing pole attached to their head. A spine projects out in front of the fish, and somewhat upward, with a frilly or luminescent bulb at its tip to lure prey. When prey comes near, the anglerfish lunges forward, “angling” and then gobbling it up.

      Predators catch prey in countless tricky ways. The anglerfish’s fishing pole is a neat curiosity, but what is more interesting is that the anglerfish just described are all female—fisherwomen, not fishermen. Is the anglerfish another example of an all-female species? Nope. Anglerfish males exist, but they are tiny and are called “dwarf males.” These anglerfish males are incapable of independent existence. They have large nostrils for homing in on perfumes released by the females and pinchers, instead of teeth, to СКАЧАТЬ