Sex is war!
In her inaugural column, The Economist's sex adviser explained to puzzled lovers why the battle of the sexes is much more than a metaphor. (This article, which was published last Christmas, has won the 1997 Glaxo Wellcome/British Science Writers award for the best feature on a science subject in a specialist periodical. The award was accepted by Olivia Judson, our science correspondent, on behalf of Dr.Tatiana.)
Dear Dr Tatiana,
I am worried. All my lovers leave their genitals inside me and then drop dead. Is this normal?
PERPLEXED IN CLOVERHILL
WITHOUT even looking at your picture, I can tell that you are a queen bee. Unfortunately, dear, your partners plug you on purpose. Their explosive acts of heroism are fatal but fruitless attempts to prevent other males from consummating your nuptial flight. If their efforts ever cause a problem for you, I suggest that you enlist-between each tryst-your many sisters to clean you up and remove any detritus.
Is your case normal? Well, although it is extreme, it is by no means unique. In the sexual wars, plugs, cements and glues to clog up the female reproductive tract have evolved repeatedly. Leaving the genitals behind is just an unusual variation of this male ploy. Life gets even kinkier, in fact. In a species of spiny-headed worm, males use their cements on each other, trying to gum up their rivals.
You see, the purpose of life, if you happen to be a gene, is to reproduce yourself as often as possible, sometimes at the expense of any rival genes that happen along. Of course, that means that males compete with males for mating opportunities, and females compete with females. But, as every boy or girl knows, the sexes compete against each other, too. Conflict is inherent in sex, engendered by the essential difference between males and females: males produce lots of tiny inexpensive sperm, and females a few large expensive eggs.
That asymmetry was noted long ago by songwriters and cynics. But only lately has science fully realisedwhat it means: that at every imaginable level, males and females-and the genes they carry-have different "interests". Their pursuit of their interests, in turn, is an engine of evolutionary change, as each sex struggles constantly to outwit and outmanipulate the other. In such a game, nobody wins by being a dupe. So manipulation by one sex quickly launches what biologists call a "coevolutionary arms race". You can guess how it works. The conflict of interests between males and females-arising, in your own case, because any given male needs to mate with you much more than you need to mate with him-means that every new weapon of manipulation or seduction evolved by one sex impels the other to work out a new defence.
In any one snapshot of time, the sexes appear quite well adapted to each other; but if you watch for generations, you should see an evolutionary conflict unfold. Boys and girls are locked in eternal Darwinian combat. Some boys, as you have found, will do anything to get a leg up, or over.
Dear Dr Tatiana,
Every year, after only a little bit of sex, my mate imprisons me in a hole in a tree-trunk. He claims that this is for my safety, but I think he's just insecure. Who is right?
TRAPPED IN ANN ARBOR
MY DEAR, your husband seems a little behind the times. Even Darwin thought that safety was an improbable explanation for the devoted and careful imprisoning behaviour of the male hornbill. It is much more likely that you are correct, and that walling you up is his way of solving a perennial problem: being sure of paternity.
In these days of DNA tests, perhaps you may be able to persuade your mate to think again. But I doubt he would agree. Genetic analysis of parents and offspring in many species-including people-suggest that females are adept at slipping off for what biologists call an "extra-pair copulation", or what the rest of us call a quickie.
Some of the biggest conflicts caused by quickies concerns the rearing of young. Males do not want to waste precious energy raising someone else's offspring, but they have trouble knowing for certain which young are their own. So natural selection has led to an impressive range of ways by which males prevent females from having quickies, and by which females sneak out to have them anyway. Your mate uses one of the more extreme strategies-but there are many others.
For example, the female chimpanzee and the lioness go for massive obfuscation. Both are so flagrantly promiscuous that all the males in a troupe or a pride must think they might be the father of every offspring, and so are less likely to kill any one of them. A lioness, for instance, requires more than 3,000 copulations to make a cub. As a result, many males pitch in.
When your mate walls you in, at least he is paying attention. Some species conduct their sexual wars without as much as a meeting between the male and female. For instance, the female abalone releases her eggs into the water and then the male comes along to fertilise them. Sperm that can penetrate the covering of an egg more quickly are the most likely to succeed in fertilisation-so any gene that contributes to rapid penetration will be favoured. But if sperm become too quick, an egg will have trouble ensuring that it is fertilised by only one sperm, and will thus cease to be viable. Any gene in the egg that contributes to slowing down the sperm will therefore also be favoured-and so on, through the rumba of time.
You see the pattern? Each sex is constantly evolving to defeat the other's machinations. Give yourself a few epochs, and you may find a way out of your hole.
Dear Dr Tatiana,
Every time I go near a woman, she tries to bite my head off. Am I doing something wrong?
QUAKING IN CAPE FEAR
IF IT makes you feel any better, you are not alone. Females of a number of species really are man-eaters. Conventional wisdom used to hold that this was good for both sexes. For instance, if the male were unlikely to survive the winter, it might suit both parties for him to sacrifice himself as an extra source of nutrients. But I'm sorry to say that recent research shows that this cannot be. The male is often eaten even before he has a chance to copulate.
As a spider, you are of course well aware that the female of your species can be more than fearsome. Man-eating is a common problem among your kind, after all. The males of many species of spider run the risk of being eaten well before they get anywhere near the lady's privates-and, once they do get there, the act of fertilisation can be a heroic and risky feat. To make things interesting, female spiders have two genital openings under their abdomen, and in order to fertilise all the eggs, sperm must be inserted into each. To do the job, you must dab sperm on specialised structures on your mouth, then cautiously tiptoe up to the female and kiss her you-know-what. Do be careful. Even while you are in the act of insemination you are liable to be nabbed. Above all, if you survive the experience, do not hang about for a post-coital cigarette.
What you really need is a bit of speedy evolution. The males of some other species have already evolved crafty ways to avoid being sexually cannibalised. The male tarantula has special structures that serve to ward off the female's fangs. Male spiders of the genus Argyrodes adopt a frat-boy approach: they present the female with a horn that emits a powerful drug. The female sucks on the horn and apparently gets high-leaving the male to have his wicked way with her. Still other spiders go in for bondage: the male will not attempt insemination until he has the female firmly tied down.
I suppose you want to know exactly why these ladies want to eat you. I wish I knew. Some evidence suggests that sexual cannibalism may not even be good for females, as their savage tendencies sometimes prevent them from getting their eggs fertilised at all.
But don't forget that males do not always draw the short straw. Wife-beating is a prevalent problem. In goldfish and Siamese fighting fish, the female can be mortally injured during mating. Goldfish may be pummelled into the sand; Siamese fighting fish may be squeezed too energetically by males hoping to extract extra eggs.
Particularly when a male is a deadbeat dad who contributes no parental care, he will want to mate rather more often than his partners, and at more inconvenient times and places. So the sex can get a little rough. Water striders-seemingly delicate insects that skate along on the tops of freshwater lakes and ponds-are renowned for the vigorous wrestling matches that have arisen out of conflict over when to have sex. In some species, females suffer tremendously increased costs by being made to mate more often than they need to, as Goran Arnqvist, a biologist at Umea University in Sweden, has shown.
Some males even resort to handcuffs and chains. In some species of water strider, males bristle with grappling hooks, claspers and spines to hold the female down. This can lead to long mating sessions-hours, sometimes. The male perches on the female's back, while she must keep moving or risk drowning. Not only is this exhausting, but the poor female is three times more likely to be eaten by predators than when she is free. The male does not suffer at all.
Feminine guile is not without its resources, however. In other species of water strider the female never goes out without mace in her handbag. She has spines and other appendages, dubbed "pepper-spray adaptations", that Dr Arnqvist has shown are excellent for clobbering pesky males. So armed, she is much more likely to mate where and when she chooses.
Dear Dr Tatiana,
I have been lucky in love: I am a hermaphrodite. However, I have recently met a pure male. We like each other, but I have heard that sex with a real man will give me hairy palms and might eventually drive me insane. Is this true?
WRIGGLING IN WORMS
GIVEN that you are a nematode, I wouldn't worry about hairy palms. Insanity, on the other hand, is a risk in all dealings with men. But you should be aware that even when sex does not bring the risk of sudden death or creeping insanity, it can still take years off your life.
The act of sex is costly for both males and hermaphrodites of your species, as David Gems, a biologist at University College London, has found. The males try to mate with anything that vaguely resembles a female-and they often copulate with other males, attempting to insert their privates into the excretory pore. Such vigorous exertions seem to be the cause of their premature demise. In the case of the hermaphrodites, however, it is not clear whether early death is simply due to the mechanical costs of copulation (as is the case for pure males) or whether something more sinister is going on.
Sinister? Yes, indeed. It is a desperate world, my dear. In the fruit fly Drosophila, males transfer substances with their sperm that are toxic and that may even manipulate female behaviour.
When a male fruit fly mates with a female, he delivers with his sperm some gunk known as the "accessory fluid". Tracey Chapman, Linda Partridge and their colleagues at University College London have shown that this love potion is more than a mere accessory to the crime: the fluid is responsible for females' dying young. Other things being equal, females who are forced to mate more often live less long. But the effect diminishes if females mate with genetically engineered males who produce sperm but lack the accessory fluid.
Mariana Wolfner, a biologist at Cornell University in New York, and Eric Kubli, a biologist at the University of Zurich, and their colleagues are analysing this fluid. It appears to be made up of roughly 80 different proteins, only a handful of which have been identified. But the data so far suggest that these proteins can have a potent and nefarious effect. For instance, one protein, known as "sex peptide", manipulates the female so that she ignores other males. Inject a virgin female with essence of sex peptide, and she will lose interest in boys and reject their advances.
Perhaps this uncharitable interpretation is a bit paranoid. The proteins could just be signals to the female that she has been inseminated, and that it is time to begin making and laying eggs. However, several lines of evidence suggest that the elixirs of love really are sexual weapons.
First, many proteins are involved, and they all seem to be evolving rapidly-a hallmark of conflict. Second, females who mate a lot, and who are therefore exposed to more of the love potion, not only live for a shorter time: they also tend to see fewer offspring into adulthood, even though they lay more eggs. This suggests that the proteins of the accessory fluid are good for the males but bad for the females.
Third, preliminary experiments suggest that females may evolve to minimise the costs of mating, either by decreasing the number of times that they mate, or by decreasing their sensitivity to the love potion's toxins. Females who are forced to mate at high rates for many generations seem to evolve rapidly so that they are less responsive to the toxins.
Such results raise an intriguing question. To what extent do males and females of other species-particularly people-manipulate each other's behaviour with chemicals? At the moment, any comment would be pure fantasy. But primate semen is a complex brew and contains chemicals whose presence is mysterious. Whether or not they could have any effect on females remains shrouded in ignorance.
Dear Dr Tatiana,
I have beautiful red eyes, I sing competently, and I am an excellent dancer. My friends tell me I am amusing company, and when I look in the mirror, I'm impressed. Yet for some reason I can't get a girl. They don't take any notice. Can you offer any suggestions on how to become irresistible to women?
MELANCHOLY IN ORANGE COUNTY
MY ADVICE is that you leave Orange County and fly north towards Santa Cruz. The southern belles seem to have evolved an apathy to good looks and fast talking. You might have better luck in a more naive population. I have consulted Bill Rice, an evolutionary biologist at the University of California, Santa Cruz, who fears that you are the innocent victim of what he calls "chase-away selection".
Dr Rice has conducted experiments on fruit flies like you. Using some fancy genetic tricks, Dr Rice allowed males to evolve for 41 generations while holding females in the same evolutionary spot. He showed that, when they are allowed to run evolutionary circles around the females, the males quickly win the arms race: they become much better able to seduce females. Females are less likely to refuse the advances of the "supermen", and will mate with them more than with regular males. This suggests that if you could move to a population where the co-evolutionary arms race has not escalated as much as it has at home, you too could be a superman.
Reversing the experiment-and seeing what happens when females can evolve and males cannot-is technically much more difficult. Instead, Dr Rice is testing another hypothesis: that males should evolve to be less manipulative of females if both sexes are forced to be strictly monogamous. The experiments are not yet finished, but Dr Rice expects that such a realignment of male and female reproductive interests would significantly ease the conflict between the sexes.
Such experiments are tantalising. If human males could evolve for 41 generations while females were held still, would they become a breed of dangerous but irresistible superlovers? We don't know. But Dr Rice reckons that the tendency to bring presents, wear colourful plumage, warble impressive songs and gyrate through complex dances may have arisen as a consequence of sexual arms races. His logic runs like this. Males that impress females are more likely to persuade them to mate. However, females should not be too easily impressed, or they will mate more often than is good for them. Thus, every new sexy trick that males evolve should soon be met with evolved boredom on the part of females. Then, in order to be sexy, the male must be even more impressive than before-and so on, ad infinitum.
Dr Rice argues that some evidence suggests that females who are used to sexy males sporting big fancy tails or some other macho accessory-sports cars, perhaps-are not particularly impressed by them, but that related females whose males are not so endowed are swept off their feet. This is a new idea and has not yet been put properly to the test. But I'm sure you'll agree it has a plausible ring.
Contrary to a widely held belief that the Internet is awash with smut, it appears that there is in fact not enough sex on the Internet. None of the research described in Dr Tatiana's column is available on the web, nor are there any photographs online of the appalling acts which she and her correspondents describe.
[ Miscellaneous | Krishna Kunchithapadam ]
Last updated: Sun Jun 27 17:00:19 PDT 2004
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