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.
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 androgens—the “masculine” hormones—while 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 aggression—and 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.
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 examples—genitalia 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 body—heads, 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 penis—a modified tentacle—which 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.
The variations on these themes are myriad, fascinating, shifting like shards of colored glass in a grand kaleidoscope, often defying prediction. My favorite e
xample is the spraying characid. This little fish lives in murky rivers in Guyana. Surprisingly for a fish, it lays its eggs out of water. When the male and female spawn, they leap out of the water together and stick themselves briefly to a blade of grass or to the underside of a leaf from a plant hanging over the bank. With each leap, the female lays eggs and the male fertilizes them. They do this over and over again until the female has laid perhaps three hundred eggs. Then, for the next three days, the male splashes the eggs with his tail to keep them from drying out. If it’s raining, he gives himself the afternoon off. Or, to take an example more similar to your own case, my hyenid friend, look at the Dayak fruit bat, who lives on the Malay Peninsula. In this species, both males and females produce milk, apparently sharing the responsibility of nursing the young. Is it any stranger for a female to have a phallus than for a fish to lay eggs out of water? Or for a male mammal to produce milk?
Gender benders. The next time anyone wheels out a stereotype and says, “She does this, he does that,” here’s your reply:
When you gaze at a couple and wonder
What trait makes him “him” and her “her,”
Beware, for it’s easy to blunder
And be false in what you aver.
Some creatures change sex before teatime,
Some others find two sexes dull,
And that virile male fish has no free time—
He’s got all his kiddies to lull.
When it comes to the topic of gender,
Mother Nature’s been having some fun.
Take nothing for granted! Remember,
You won’t find any rules—not a one!
13
WHOLLY VIRGIN
No doubt, many of you have been writing to me over the years because you’ve seen my popular TV program, Under the Microscope —The Deviant Lifestyle Show! You’ll know that the program’s had a lot of kinky, if not downright perverted, guests, and of course the audience is used to hearing about weird sexual practices. A few weeks ago, however, we had a really provocative guest. I don’t know if you saw the episode, but the most awful fight erupted—there was practically a riot, and I’m sorry to say I almost lost control of the show.
I’m not surprised everyone got so upset. The guest in question doesn’t have any weird sexual practices—or indeed, any sex at all. Worse, no one in her family has had sex for more than eighty-five million years. This is an outrage: scientists cannot agree on what sex is for, but they all agree that it is essential, impossible to live without. And yet if our guest can manage without sex—or men—why can’t the rest of us? What’s sex good for? Is it passé? Are men endangered? Such questions bring us to the heart of perhaps the most fundamental, controversial matter in biology—what is sex for?—and since most aspects of the topic were hashed out on the show, here’s my account of the furor.
We had the biggest turnout yet. All the usual crowd were there—the belligerent ram and his supercilious armadillo friend were both sitting in their regular places in the front row. The pocket mouse was curled up in the small-animal gallery; the homing pigeons were on their customary perch. As always, Moby, that impressive puffer fish from the Congo River, was churning up and down the freshwater fish tank. But a lot of the members of the audience were first-timers. I noticed a bake—if that’s the right collective noun—of clams in a corner of the saltwater tank. Several Brazilian lizards, looking rather sickly and depressed, had stationed themselves halfway up the left wall. The back rows were bristling with radical feminists wearing T-shirts that said, “Men, who needs them?” and “Sex is for wimps.” The studio was fizzing with excitement and hostility. The cause of all the agitation? My guest, none other than Miss Philodina roseola, the bdelloid rotifer.
From looking at her, you’d never guess Miss Philodina is at the heart of one of the most notorious scandals in evolution. Slender and translucent, she looks less like an animal than like a pocket telescope blown out of pale pink Venetian glass. But you don’t normally see telescopes eating algae, and before the show Miss Philodina had clearly been doing just that. Throughout the entire evening, the remains of a recent feast were greenly visible through her glassy body. (This was my fault: I usually advise translucent guests to skip lunch the day of the show, but this time I forgot.) Her most striking feature, though, is on top of her head, where she has a pair of disks edged with beating cilia, tiny mechanical hairs whose motion gives the illusion of wheels spinning round and round. Of course, she’s barely half a millimeter tall, so before anyone could get a look at her, we had to settle her on a comfortable frond of moss and turn on the microscope so as to project her blown-up image on the screen by my chair. We cut a fine pair, the two of us. I looked my usual glam self in my best scarlet suit. She looked the picture of innocence. And that innocence was the cause of all the trouble …
The show started off much as usual. I welcomed the audience and introduced Miss Philodina, giving a few trivial details, such as her favorite spot to hang out (damp moss) and the fact that rotifer means “wheel bearer.” Everyone in the audience applauded on learning that her Latin name means “rosy lover of twirling.” But as soon as I began to talk about the nature of her deviancy, the disturbance began.
Me: Tell us, Miss Philodina, when was the last time anyone in your family had sex?
Miss P.: Hmmm. I think it’s been about eighty-five million years since anyone in my family has even been on a date.
Me (To audience): And you thought you had problems. (To Miss Philodina): No sex, not even a kiss, since before the dinosaurs went extinct. And why not?
Miss P.: My ancestors abolished males. They said they were better off without them.
The studio drowned in jeers and whistles—despite loud cheering from the radical feminists.
Me: So how do you reproduce?
Miss P.: We clone ourselves.
Well, that caused absolute mayhem. The pocket mouse even fainted. But I’ve seen this reaction before. Many animals, especially mammals, have a horror of cloning. They seem to think it will produce a flock of monsters or something. So I had to remind everyone that cloning is nothing more than reproducing without sex—something that billions of respectable organisms are doing every day. I paraded my standard examples: strawberries sending out runners and shoots; yeasts and other organisms budding off bits of themselves; sponges, sea anemones, and worms of various kinds falling to pieces and regenerating, whole new animals growing from each piece; all sorts of girls (including bdelloid rotifers) laying asexual eggs. And to the discomfiture of many in the audience, I pointed out that even mammals clone once in a while, when an embryo splits early in development. The resulting individuals are not usually called clones, though. “Twins” is considered more polite. Typical mammalian political correctness.
It’s curious. Everyone always forgets there’s nothing wrong with cloning from time to time—that cloning mixed with bouts of sex can contribute to a healthy and happy lifestyle. As I explained to the audience, it’s only giving up sex altogether that’s the problem.
At first glance, however, giving up sex seems advantageous—from a genetic point of view, anyway. Sex may be fun, but cloning is much more efficient. All else being equal, an asexual female who appears in a population should have twice as many offspring as her sexual counterpart. To see why, think of it this way. In a sexual population—the human population, for example—each female must have two children for the population to remain the same size. If females have fewer than two children, the population shrinks; more than two, and the population grows. In an asexual population, however, each female needs to have only one child for the population to remain the same size. More than one, and the population will grow.
But although asexuality often evolves—it pops up in groups from jellyfish to dandelions, from lizards to lichens—it rarely persists for long. On the great tree of life, asexual groups are out on the twiggiest twigs of the twiggiest twigs: lots of buds, no branches. After a brief and glorious flowering, asexual
s vanish. Which has led scientists to conclude that exclusive asexuality is an evolutionary dead end, a fast track to extinction. Sex, they insist, is essential. And ancient asexuals—creatures such as the bdelloid rotifers that have lived without sex for millions of years—should not exist. According to all the theories, the bdelloids should have disappeared shortly after giving up sex.
Yet, in scandalous defiance of scientific prediction, there’s Miss Philodina, thumbing her wheels at us from the frond of moss. How come these rotifers have succeeded where so many others have failed? Or, to get back to the central question, if they can do without sex, why can’t the rest of us?
With that preamble, I opened the floor to questions, as usual reminding the smallest members of the audience to step up to the microscope in the aisle. Understandably, the first questions challenged Miss Philodina’s claim. What did she mean when she said no one in her family has sex? Did she simply mean that bdelloid rotifers get intimate but avoid genital contact? No, that’s not what she meant. But before she could go on, there was a truly embarrassing incident. Two bacteria tried to have sex on live TV
The screen on the wall lit up: someone in the audience had gone to stand under the microscope. Gradually, the image came into focus to show not one but two lozenge-shaped organisms. In actual size, each would’ve been about a millionth of a meter—tiny even in comparison to Miss Philodina.
One of them started to squeak: “Good evening, everybody. We’re a pair of bacteria of the species Escherichia coli—E. coli to our friends. Many scientists keep us as pets, so we often live lives of luxury and ease in the laboratory. In the wild, we live in the guts of mammals, helping digest food.
Dr. Tatiana's Sex Advice to All Creation Page 19