Dr. Tatiana's Sex Advice to All Creation (21 page)
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Authors: Olivia Judson
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As a general rule, flexible gender is expected to evolve whenever an individual's reproductive success as a male, female, or hermaphrodite differs greatly according to circumstances. Social milieu may not be the sole influence at workâif, for example, males can't reproduce successfully unless they are big, it could be advantageous to start life as a female and become male only on achieving a good size. The ability to choose your sex is particularly handy, however, when being one sex leads to a riskier life than being the other.
Which brings me back to you. A female green spoon worm takes a greater gamble in life than a male does. She needs two years to mature, during which she may be eaten by a bat ray, and on reaching adulthood she may never find a mate. So it makes
sense for a larva who meets a female to become male: not only is he guaranteed a mate, but he can start reproducing as soon as he's installed himself. What is it about you that makes a larva want to be a man? Well, your lovely bulbous bodyâbut particularly your long, twitchy proboscisâsecretes a substance known as bonellin, after your formal name,
Bonellia viridis.
A whiff of bonellin makes any larva stand up and fly right.
sense for a larva who meets a female to become male: not only is he guaranteed a mate, but he can start reproducing as soon as he's installed himself. What is it about you that makes a larva want to be a man? Well, your lovely bulbous bodyâbut particularly your long, twitchy proboscisâsecretes a substance known as bonellin, after your formal name,
Bonellia viridis.
A whiff of bonellin makes any larva stand up and fly right.
But what you're really dying to know, I suspect, is why your lovers are so minute: what strange circumstances prompt natural selection to reduce a man to a testicle? Two factors are thought to be conspiring here. The first is if females are sedentary, the second if they are sparsely sprinkled across the landscape. Then a male's biggest challenge is finding a mate. The smaller he is, the faster he can mature (he doesn't have to waste time growing) and the sooner he can start looking.
This size business is not just a quirk of green spoon worms: lilliputian lovers appear in widely separate groups. Take anglerfish, monsters that live in the coldest, deepest seas. The females don't swim much but float in the darkness, ready to ambush their prey. Like wreckers of old, these formidable girls have special dangles and lanterns to lure the curious to their doom. Victims are swallowed whole, engulfed by toothy mouths and grossly distendable stomachs. Like your hubby, male anglerfish are minute. But these guys win the all-species Cyrano de Bergerac Award for the largest nose in proportion to body size. Presumably, the males follow their noses to find females in the vasty deep. When they meet one, they bite into her leathery black underbelly and fuse with her body, becoming a permanent appendage, little more than a pair of gonads. Still, it seems to me, their fate isn't quite as ignominious as a life sentence in your small man room.
Dear Dr. Tatiana,
Â
I'm a spotted hyena, a girl. The only trouble is, I've got a large phallus. I can't help feeling that this is unladylike. What's wrong with me? Can anything be done?
Â
Don't Wanna Be Butch in Botswana
No one expects hyenas to be ladylike. Least of all the biggest and baddest of them allâthe spotted hyena. The brown hyena and the striped hyena squabble with vultures over a rotting carcass, and both sometimes eat fruit. The aardwolf, a dainty black and white hyena, eats harvester termites, lapping up more than 200,000 a night with its sticky tongue. But the spotted hyena is a fearsome predator. A single hyena can run down and kill an adult male wildebeest, an animal more than three times its weight. And despite their respective reputations, lions scavenge from hyena kills more often than the other way around. At least, they do if they get there in time. A spotted hyena can devour a Thomson's gazelle fawn (2.5 kilos or 5.5 pounds) in under two minutes. Twenty-one hyenas can dispose of a yearling wildebeest (100 kilos or 220 pounds) in thirteen minutes, and there won't be much trace of him left. Having massive jaws, hyenas can pulverize bones, even rhinoceros bones, and not just to get to the marrow: unlike other carnivores, hyenas can digest bones. That's why hyena scats are whiteâthey're mostly bone powder. All the same, the first hyena on a kill will begin by taking delicacies such as the victim's testicles or udders, or a fetus if there is one.
So you see, yours is no tea-drinking, cake-eating, genteel society; ladies would be distinctly out of place. And not just with respect to table manners. Spotted hyenas typically live in big groups, each presided over by a dominant female. But while they
sometimes hunt in packs (especially when hunting zebra), cooperation on anything else is rare. Instead, it's a mad scramble. That's one reason hyenas eat so fastâthey gobble as much as they can before anyone else arrives. The only moderating influence is the social hierarchy, aggressively enforced, where the dominant female and her cubs take precedence over everybodyâand all other females take precedence over all other males. Unlike the other hyena species, where males and females are roughly the same size, but like many birds of prey, female spotted hyenas are bigger and heavier than males. But a phallus? At least no one can accuse you of penis envy.
sometimes hunt in packs (especially when hunting zebra), cooperation on anything else is rare. Instead, it's a mad scramble. That's one reason hyenas eat so fastâthey gobble as much as they can before anyone else arrives. The only moderating influence is the social hierarchy, aggressively enforced, where the dominant female and her cubs take precedence over everybodyâand all other females take precedence over all other males. Unlike the other hyena species, where males and females are roughly the same size, but like many birds of prey, female spotted hyenas are bigger and heavier than males. But a phallus? At least no one can accuse you of penis envy.
On the outside, male and female genitalia look so similar that for many years the spotted hyena was thought to be a hermaphrodite. In females, however, what looks like a phallus is actually a grossly enlarged clitoris, fully capable of erection. The lips of the vagina have fused shut and form a pseudo-scrotum. Urination, copulation, and birth must, therefore, be done through the clitoris.
How? Well, if you really want to know ⦠At puberty, the mouth of the clitoris becomes elastic, able to open to about two centimeters (one inch) in diameter. To allow copulation, the female retracts the clitoris, folding it up like a concertina, thus creating an orifice and allowing the male to slide in. It's the birth of a spotted hyena, however, that is particularly bizarre. For starters, the birth canal is a funny shape. Instead of being a straight passage as in most mammals, it features a sharp bend. Worse, at sixty centimeters (twenty-three inches), it's twice as long as in other mammals of a similar size. The umbilical cord, however, is shortâonly eighteen centimeters (seven inches) long. Once the placenta detaches, the young hyena will asphyxiate if it is not born promptly. But a baby hyena's head is too big to pass through the clitoris. So when a mother gives birth for the first time, the clitoris tears to
let the cub out. This is not just agonizing. It is often lethal. Scientists estimate that more than 10 percent of females die the first time they give birth, and more than half of firstborn cubs are stillborn. (Paradoxically, since the clitoris never recovers from this trauma, subsequent births don't put the mother's life at risk.)
let the cub out. This is not just agonizing. It is often lethal. Scientists estimate that more than 10 percent of females die the first time they give birth, and more than half of firstborn cubs are stillborn. (Paradoxically, since the clitoris never recovers from this trauma, subsequent births don't put the mother's life at risk.)
So here we have a strange set of facts. Chief among them is that the female spotted hyena has a reproductive organ that exacts huge costs. This demands explanation. Either the organ itself must confer some giant benefit or it must have evolved as an unfortunate by-product of some
other
trait that confers a giant benefit.
other
trait that confers a giant benefit.
Let's start with the organ itself. Two advantages have been proposed. The first is that in having a structure that mimics the phallus, the females can take part in greeting ceremonies: when spotted hyenas meet, they stand head to tail and inspect each other's erect members. Female participation in the ritual might therefore help them exert their dominance over males. Although this idea will appeal to any Freudians out there, it hardly seems sufficient to explain such a deadly organ.
The second possibility is even more flimsy. The mechanics of spotted hyena sex are so tricky that females are able to resist unwanted advances: copulation requires full cooperation; rape is impossible. But rape has never been reported in any hyena species. Moreover, since female spotted hyenas are so much bigger than males and have such big teeth, courting males are unusually polite, literally bowing and scraping as they approach. Females hardly need a phallus for self-defense.
Neither of these explanations is exactly convincing, I think you'll agree. What about the phallus being a by-product of natural selection for Something Else? At first glance, this seems more plausible. There's a good candidate for the Something Else: aggression. We know hyena society is aggressive, and it's easy to
imagine that aggressive females do better than shrinking violets. Moreover, the fetal hyena is exposed to high levels of testosterone and other androgensâthe “masculine” hormonesâwhile in the womb. Intrauterine exposure to these hormones fosters aggression: female mice that are snuggled between their brothers during fetal life are exposed to higher levels of androgens than females nestled between sisters and are more aggressive as grown-ups. And crucially, intrauterine exposure to high levels of androgens can cause profound genital abnormalities. In humans, for example, excessive exposure to androgens in the womb gives a girl a greatly enlarged clitoris and a vagina that is partially fused shut. So the question is, could increased aggression in female spotted hyenas be sufficiently favored by natural selection to offset the costs of copulating and giving birth through the clitoris?
imagine that aggressive females do better than shrinking violets. Moreover, the fetal hyena is exposed to high levels of testosterone and other androgensâthe “masculine” hormonesâwhile in the womb. Intrauterine exposure to these hormones fosters aggression: female mice that are snuggled between their brothers during fetal life are exposed to higher levels of androgens than females nestled between sisters and are more aggressive as grown-ups. And crucially, intrauterine exposure to high levels of androgens can cause profound genital abnormalities. In humans, for example, excessive exposure to androgens in the womb gives a girl a greatly enlarged clitoris and a vagina that is partially fused shut. So the question is, could increased aggression in female spotted hyenas be sufficiently favored by natural selection to offset the costs of copulating and giving birth through the clitoris?
Maybe. Spotted hyenas begin as they mean to go on: with their teeth bared. Most hyenas are born in litters of two, and whichever is born first will attack the second within minutes. Death often results. Killing your sibling allows you to monopolize your mother's milk; since spotted hyenas nurse for more than a year, successful siblicide increases your own chances of living to adulthood. Thus, one idea is that high levels of androgens in the womb are favored because they promote violence among cubs at birth. This fails to explain, however, why siblicide is more frequent among same-sex pairs than among pairs of opposite sex and why it is even more frequent among pairs of females than among pairs of males: if siblicide were the explanation, you wouldn't want any sibling, whatever its sex.
A more convincing explanation says that aggression is favored because dominance relationships are mediated by aggressionâand there are considerable benefits to being dominant. Compared with their more lowly peers, high-ranking females
become pregnant younger and have shorter gaps between litters, and more than twice as many of their offspring survive to adulthood. This is a big difference and could potentially offset the cost of the phallic clitoris.
become pregnant younger and have shorter gaps between litters, and more than twice as many of their offspring survive to adulthood. This is a big difference and could potentially offset the cost of the phallic clitoris.
Alas, however, the puzzle can't be solved so neatly. Studies of the spotted hyena clitoris show that blocking the circulation of androgens in the womb does not cause reversion to “typical” female genitalia. A large component of the development of the phallic clitoris is thus independent of these hormones, undermining the idea that the phallus is a by-product of natural selection for increased aggression. So until we know more about how the structure develops, I'm afraid the reason for your singularly costly phallus will remain a mystery.
But your situation does illustrate a more general point. That is, beyond the basic fact that males make sperm and females make eggs, there are no rules, not even in what appear to be the most stereotypical gender-related areas. Let me give you two examplesâgenitalia and child care.
In countless groups of animals, females have evolved internal fertilization, presumably because it is an effective way of ensuring that egg meets sperm. Internal fertilization can be achieved by the female's squatting over a sperm packet, as it is in some mites and some amphibians, for example. But often the evolution of internal fertilization is accompanied by the evolution of a penis, a structure to deliver sperm. The penis has been reinvented more often than the wheel. Which explains why, in different groups, this symbol of masculinity is formed from different parts of the bodyâheads, mouths, legs, tentacles, fins, and so on. Some of the reinventions are pretty quirky. The spider, for example, is stuck with the penis equivalent of a triangular wheel. The male, as you may recall, delivers sperm with pedipalps, modified mouthparts. Inconveniently, however, the pedipalps have no connection to the
part of the body where sperm is made, so before copulating, the male deposits a drop of sperm on a small web that he spins for the purpose. He then draws the sperm up into his pedipalps, like someone drawing ink into a fountain pen. In the seahorse, it's the female who has the penis, to deliver eggs into the male's brood pouch. One species of sea slug,
Sapha amicorum,
a tiny hermaphrodite from the Red Sea, actually has its male genitalia inside its mouth, and copulation is an extraspecial kiss. Lucky they don't have to go to the dentist. But perhaps the oddest approach I've come across is practiced by three obscure relations of the octopus, all of which have abandoned the seafloor for open water. The paper nautilus, the best known of the trio, is an ethereal creature. Bright white, with hints of purple, blue, and red, the female lives in a beautiful white shell and floats through the water. The male is tiny, and hardly anyone has ever seen him. Not even his mate. What appears to happen is that he fires off his penisâa modified tentacleâwhich takes up an independent life within the female, who may entertain several such guests at once. This is so weird that it's not surprising early naturalists thought the penises were parasitic worms. Imagine the lonely-hearts advertisement of a female paper nautilus: “Fire and forget. Send your organ to a loving home.”
part of the body where sperm is made, so before copulating, the male deposits a drop of sperm on a small web that he spins for the purpose. He then draws the sperm up into his pedipalps, like someone drawing ink into a fountain pen. In the seahorse, it's the female who has the penis, to deliver eggs into the male's brood pouch. One species of sea slug,
Sapha amicorum,
a tiny hermaphrodite from the Red Sea, actually has its male genitalia inside its mouth, and copulation is an extraspecial kiss. Lucky they don't have to go to the dentist. But perhaps the oddest approach I've come across is practiced by three obscure relations of the octopus, all of which have abandoned the seafloor for open water. The paper nautilus, the best known of the trio, is an ethereal creature. Bright white, with hints of purple, blue, and red, the female lives in a beautiful white shell and floats through the water. The male is tiny, and hardly anyone has ever seen him. Not even his mate. What appears to happen is that he fires off his penisâa modified tentacleâwhich takes up an independent life within the female, who may entertain several such guests at once. This is so weird that it's not surprising early naturalists thought the penises were parasitic worms. Imagine the lonely-hearts advertisement of a female paper nautilus: “Fire and forget. Send your organ to a loving home.”
Child care is another of Mother Nature's favorite inventions. It has evolved, to different degrees, in an astonishing diversity of organisms, and mothers have no monopoly on the activity: depending on the species, the carer may be hermaphrodite, male, or female. Take leeches. These bloodsucking hermaphrodites often perform rudimentary parental care, guarding their egg cocoons from predators. But some go further. The African leech,
Marsupiobdella africana
, has adopted the habits of a kangaroo and carries its young in a pouch. And the leech
Helobdella striata
not only carries its young glued to the belly of the parent but hunts
small worms for them to eat. Or take frogs. Most frogs spawn, and that's it. But in a few, child care is elaborate. Green poison arrow frogs go to great lengths for their tadpoles. These small, elegant creatures live in the leaf litter of Central American forests. As their name suggests, their chief claim to fame is that their skins are toxic. Humans living in the forests wipe their darts on the frogs' backs, collecting venom to paralyze the animals they hunt. However, these frogs deserve fame for another reason: they are a paragon of fatherhood. Once a male and female have courted, the female lays a small clutch of eggs in the leaf litter. The male tends the eggs, sitting in a puddle, then returning to sit on the eggs to keep them moist. He uses his puddle jaunts to search for pools where he can drop the tadpoles when they are ready. A pool might be the accumulation of rain in the top of a pineapple or a cranny of a tree trunk. When, after a couple of weeks, the tadpoles hatch, he carries them, one at a time, to his chosen pools and drops them in.
Marsupiobdella africana
, has adopted the habits of a kangaroo and carries its young in a pouch. And the leech
Helobdella striata
not only carries its young glued to the belly of the parent but hunts
small worms for them to eat. Or take frogs. Most frogs spawn, and that's it. But in a few, child care is elaborate. Green poison arrow frogs go to great lengths for their tadpoles. These small, elegant creatures live in the leaf litter of Central American forests. As their name suggests, their chief claim to fame is that their skins are toxic. Humans living in the forests wipe their darts on the frogs' backs, collecting venom to paralyze the animals they hunt. However, these frogs deserve fame for another reason: they are a paragon of fatherhood. Once a male and female have courted, the female lays a small clutch of eggs in the leaf litter. The male tends the eggs, sitting in a puddle, then returning to sit on the eggs to keep them moist. He uses his puddle jaunts to search for pools where he can drop the tadpoles when they are ready. A pool might be the accumulation of rain in the top of a pineapple or a cranny of a tree trunk. When, after a couple of weeks, the tadpoles hatch, he carries them, one at a time, to his chosen pools and drops them in.
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