by Robin Baker
Why is it so important to a woman to prevent or, failing that, detect her partner’s infidelity? What are the repercussions of failure for her pursuit of reproductive success?
A woman has a lot to lose from her partner’s infidelity. And many, though not all, of the dangers are the same as for a man. First, there is the risk that she will have to share his wealth, time, energy and other resources with the other woman. Secondly, there is the danger that he will eventually leave her for the other woman, reducing his support for her still further. Whichever of them looks after the children, they face the dangers of single-or step-parenthood which we discussed in relation to Scene 9. Thirdly, there is the greater risk of contracting sexually transmitted diseases, because her partner is at greater risk. There is one risk, however, that does not affect her. Unlike a man, she is in no danger of being tricked into raising any children by her partner’s lover. This means that, on balance, infidelity is slightly less of a threat to a woman than it is to a man.
This conclusion is as applicable to monogamous birds, monkeys and apes as it is to humans. The result is that, although both males and females of all these species try to prevent their partner from being unfaithful, males are significantly more possessive of their partner than are females. They are significantly more aggressive, and significantly less forgiving. Females may attempt to drive away other females. They may attempt to intervene between their mate and another female. They may even desert their young if they receive too little time and help from their partner. However, since their physical commitment to preventing infidelity is less than the male’s, they are less likely to desert if their partner is unfaithful. The same is true for humans.
Women do sometimes wound or kill a partner if he is unfaithful. They do sometimes wound or kill his lover, leave their partner or drive him out, and they also sometimes abandon their children to him to raise. But again, they are less likely to do all of these things than are men and are more likely to overlook discovered indiscretions. Nevertheless, the threat of retribution is always there, and real enough for most men to attempt to hide their infidelity.
Arguably, male animals are never quite as subtle over their infidelity as females, maybe because the costs of discovery are less. My favourite description of sophisticated infidelity on the part of the female concerns a small brown bird, the dunnock. The male and female, the epitome of contented monogamy, were first seen as they hopped side by side across a lawn, pecking up morsels of food. When they reached a bush, the male went round one way, the female the other. As soon as the bush shielded her from her partner, the female flew in an instant into dense vegetation nearby. There, she copulated with a lurking male, then flew back to her position behind the bush. A few seconds later, male and female hopped back into each other’s view, past the bush. Still intently pecking at morsels, the female acted as if nothing had happened.
Nearly as appealing is the film, shown worldwide, of a female monkey foraging on the ground for food while being watched attentively from a high branch by her consort. Alongside her comes another male. He sits down, innocently picking at himself, hiding his erection from her consort. Every time the consort’s attention is distracted, the other male taps the female on the shoulder. In an instant she stands and presents and the male inseminates her. So quick is their intercourse that by the time her consort looks back in their direction, they have resumed their previous activities – innocence personified.
Maybe a female dunnock who flies into vegetation is no more subtle than a male who hides there, waiting. Maybe a female monkey who feigns innocence until her partner is distracted is no more sophisticated than a male who hides his erection and inseminates at the speed of light. And maybe a woman who has sex with the window-cleaner while her partner is at the shops is no more sophisticated than a man who has sex with his secretary in a cupboard at the office party. But, on balance, one always has the feeling that the female of the species, whatever the species, has that slight edge when it comes to ingenuity and imagination. As far as humans are concerned, the best we can use as evidence is that, taking thousands of instances into account, the man is more likely, on average, to have his infidelity discovered than the woman.
In Scene 11, the woman needed to check her mate’s genitals only superficially to confirm his infidelity. Had he been more cautious and washed himself before returning home, he might have escaped detection. Had he fabricated a better story, he might, again, have escaped detection. But he did neither, and suffered the consequences. From the moment his infidelity was uncovered, his partner decided that when the right moment came she would leave him, rather than wait for him to leave her.
Had the man’s infidelity not been discovered, he would probably have done better reproductively: at the very least, he would have had the chance of a third child with his partner. As it was, he did not. Nor did he manage to compensate for this loss by siring a child via infidelity or via a second longer-term partner. He nearly succeeded in fathering a child by another man’s partner, but failed. He nearly attracted another fertile partner through his infidelity, but failed when it came right down to it. Any further chance he had of producing children faded when he contracted gonorrhoea (at least half of all human infertility is due to sexually transmitted disease). Even if he had remained fertile, his age and reduced circumstances made him less attractive to fertile women. Instead, his major reproductive strategy became his partnership with an older, probably post-menopausal, woman - in the sense that, with her help, his children will probably have left home fully able to realise their reproductive potential. Eventually, they would give him grandchildren. Had his infidelity not been discovered, he might have had more grandchildren, but at least he had some.
Had the woman not discovered her partner’s infidelity, she would probably have done worse reproductively. Of course, she might have had another child with him. But all the time she was with him, she would unknowingly have been vulnerable to sudden desertion and decreased support. As it happened, she would also eventually have contracted gonorrhoea and risked future sterility. Instead, her discovery helped her to take advantage of his support for five more years, then pick her moment to leave him for another man and a second family. She will have ended up with the same number of grandchildren as him via their mutual children, plus more via the children in her second family.
Reproductively, infidelity has the potential to benefit both men and women, as we shall see later in this book. However, as these last four scenes have shown, it can also be costly even if it is successfully hidden from the partner. On top of this, however much a person may suffer from their own infidelity, they are likely to suffer even more if their partner is unfaithful – especially if they fail to detect it.
Sometimes the benefits of infidelity will outweigh the costs and sometimes they will not. As we noted earlier, the reproductive successes of each generation will be those people who, consciously or subconsciously, judge correctly when it is and when it is not advantageous to be unfaithful. Then, when infidelity is judged to be advantageous, the most successful will be those who hide their own infidelity while preventing or at least detecting their partner’s. The reproductive failures will be those who misjudge their situation, fail to hide their own infidelity or fail to prevent or detect their partner’s.
Because of these conflicts of interest, there is very little variation in the strategy shown by men, women and virtually all other species of animals which form long-term relationships – to attempt secret infidelity on the one hand while preventing a partner from doing the same on the other.
5
Secret Anticipation
SCENE 12
A Double Life
Another day at work was over, and the man on the fifth floor was just leaving for home. As he stepped into the lift, his eye was caught by a new piece of graffiti. He smiled. In colourful slang it implied that the boss of their section was not to be trusted – because he spent too much time masturbating.
The lift stopped
on the third floor and a young girl stepped in. He had seen her only once before, but she had immediately won a starring role in his fantasies. She was new to the section, an extra secretary for the man who was the target of the graffiti. He watched her face as the door closed. She saw the words immediately. Her eyes flicked sideways and caught his. They smiled at each other and she blushed, but nothing was said. When the lift reached the ground floor and they stepped out, she turned right and he turned left, heading for the car park and home.
Thirty minutes later, he drove into his garage. Once in the house he kissed his partner, admired his children’s latest drawings, and went upstairs to undress for a shower. Even as he was locking the bathroom door, he was handling his genitals, encouraging an erection. By the time he had shut the cubicle door and switched on the shower, his penis was ready for action. As he pumped himself, he searched through his mind for a sexual image. For about the tenth time in recent months, he tried mentally undressing his partner’s sister, but the image was losing its power. He tried undressing her again, this time from the back, but it still failed. Then he remembered the young girl in the lift. OK, so the lift breaks down between floors. They both undress, he kneels down, she stands astride him, begins to crouch in order to sit on his erect penis, and . . . But there was no need for an ‘and’. With that image, he ejaculated, flushed the semen down the plughole, then continued with his shower as if nothing had happened. The whole exercise had taken about two minutes.
As he showered, he mused over these routine urges to masturbate. It was as if he had a double life – sex with his partner on Saturday and Sunday, sex with himself on Tuesday and Thursday. Sometimes an occasion would be missed, sometimes an occasion would be gained, but on the whole these were his two routines.
Of course, his sex life with himself was not entirely routine. There had been the occasional highlight, particularly when he was younger. A goodnight kiss with a new girl, or a heavy but unconsummated petting session at a party, had both at one time or another sent him into a toilet to seek relief in ejaculation. Even now, an erotic scene at the movies or on TV would sometimes have the same effect. Such highlights apart, though, his sex life with himself was as much a routine as his sex life with his partner. Usually, just like tonight, it was barely even sexual, having more in common with urination and defecation than with intercourse and sexual excitement. There was little urgency, little excitement, and little feeling of satisfaction – just a feeling of relief.
Most men should be able to identify with this scene. For two-thirds, their very first ejaculation will have been triggered by self-stimulation. Over 98 per cent will masturbate at some time in their lives. Moreover, virtually all will have done so by the age of twenty. However, despite such widespread practice, few men would view their habit of shedding sperm as an important weapon in their pursuit of reproductive success. Yet this is just what it is. Scene 12 is the first of three in this chapter, each of which explores one or more aspects of the shedding of sperm (through masturbation or ‘wet dreams’).
How often a man masturbates depends on how old he is and how often he ejaculates for other reasons. On average, how often he ejaculates altogether (intercourse, masturbation, and nocturnally) will closely reflect his rate of sperm production. This varies from man to man, depending on the size of his testes. It also varies with age. From almost immediately after puberty to the age of about thirty, an average man produces around three hundred million sperm a day and ejaculates between three and four times a week. By the age of fifty these rates have dropped to about 175 million a day and to twice a week and, by age seventy-five to about twenty million a day and to less than once a month. If a man under thirty has intercourse three times or more a week, he will rarely masturbate. If he has sex only once a week, he will probably masturbate about twice.
Men are not the only mammals to shed sperm through masturbation. Dogs, of course, are notorious for such behaviour. One of their habits is to affectionately clasp a person around the knee with their front limbs and to rub their genitals up and down the dismayed person’s leg. Albeit using other methods of self-stimulation, a wide range of other species, such as rats, mice, squirrels, porcupines, pigs, deer, whales, elephants and monkeys, are also known to shed their sperm. Just like men, the males of these species will often masturbate between routine inseminations of females.
Masturbation may not seem a very sophisticated activity, but it is. It is the means by which an active, or hopeful, man tailors his next inseminate to its likely circumstances. By anticipating what those circumstances might be, he can use masturbation to adjust the age and number of sperm he will then introduce into the potential female. Not only that, but he can also adjust what proportion of those sperm will be blockers, killers and egg-getters.
A man’s body can distinguish between masturbation and insemination. The ejaculates produced are not identical. Many factors influence the number of sperm introduced during intercourse - such as how many are needed to top up his partner and to succeed in warfare, given the perceived level of risk. But, apart from a man’s age, only one major factor – time since last ejaculation – affects the number shed during masturbation. When a man masturbates, he voids about five million sperm for every hour since he last ejaculated. This seems to be the rate at which sperm exceed their sell-by date as blockers, killers and egg-getters.
Sperm change their roles as they age. Most are killers when they are young and blockers when they are old. Killers need to be full of energy and movement and to have a cap full of lethal chemicals (Scene 7). Blockers, however, can be old. Or, to put it another way, the only use for geriatric sperm is as blockers. To block a cervical channel, a sperm needs to have just enough energy to swim out of the seminal pool and travel a little way into the cervical mucus. Then it can simply coil its tail and sit still. It can even die if it wants. The channel will still be blocked.
Egg-getters also change with age. Important chemical changes have to take place on an egg-getter’s surface before it can penetrate an egg, changes that do not occur until the sperm gets close to the fertilisation zone in an oviduct. As a result, an egg-getter’s life is divided into two phases of activity. It has its first burst of energy before it is fertile – this is when it surf-boards and swims to the rest area in an oviduct. Then, during its brief phase of fertility, it has a second burst of energy – when it reaches, then swims through, the zone of fertilisation. After that, it dies.
The two columns of sperm queuing to be ejaculated (Scene 4) are not just a homogenous, characterless mixture. Inevitably, those at the front of the queue, near the man’s urethra, are the oldest. The ones at the back, way down in his testes, are the youngest. There may be some mixing of ages as the sperm are loaded into the urethra. Even so, when he places his seminal pool at the top of a woman’s vagina, the oldest sperm tend to be introduced first and go to the bottom of the pool. Younger sperm arrive in later spurts and go to the top.
The younger sperm, being more active, will be the first to enter the cervical mucus. Older sperm leave the pool more slowly. Very old sperm cannot leave the pool at all and are doomed to be ejected by the woman in her flowback. From their position higher up in the seminal pool, the younger sperm may have to swim down through groups of older ones before they can swim up and enter the elephant’s trunk of the cervix. Much depends on how deeply the cervix dips into the pool. Too many old sperm in the pool hinder the youngsters as they try to escape into the cervix.
Masturbation between intercourses usually means that a man inseminates his partner with fewer sperm than if he had not masturbated. However, the sperm he introduces are younger, more dynamic, and less hindered by supernumerary geriatric sperm. As a result, just as many, if not more, manage to escape the seminal pool and stay in the woman. Moreover, the sperm which escape are younger and more active – altogether a more efficient army.
All the same, a man needs to inject some old sperm as blockers - as many as are needed to top up the population of blockers
in his partner’s cervical mucus. For three days after a couple’s last routine intercourse, the ageing of sperm in a man’s tubes tracks the loss of blockers in his partner’s cervix with exquisite precision. Given any gap between successive intercourses of from thirty minutes to three days, he can introduce into his partner the perfect ejaculate to top up her population of blockers. Once the gap exceeds three to four days, however, his sperm queue develops an excess of blockers. This happens because there are only so many channels in the cervical mucus, and once he has enough old sperm to block these, any further blockers are redundant. In fact, they are worse than redundant, for they probably hinder the escape of his younger sperm from the seminal pool into the cervix. Beyond a certain point, therefore, the man’s best policy is to shed the oldest part of his column of sperm before inseminating a woman, rather than leaving them for her to eject in her flowback. This is one of the functions of masturbation.
If the gap between inseminations exceeds four days, the ideal inseminate is produced by masturbating two days before the next intercourse. This gives a man two sperm columns, each with about twenty million aged blockers at the front of the queue and from a hundred million to five hundred million younger blockers and killers further back. Scattered among these younger sperm are egg-getters, in a ratio of about one egg-getter to ninety-nine kamikaze types. About 10 per cent of the egg-getters are already at their peak of fertility and will go immediately to the oviduct. The remainder will reach their peak at different times over the five days after insemination.
This profile allows a man maximum flexibility in adjusting his sperm army according to the risk of warfare. If he has guarded his partner closely since they last had sex, he needs to introduce into her a full quota of blockers but only a few killers and egg-getters. So he injects all of the blockers at the front of the queue, plus a small portion of the queue behind containing the killers and egg-getters. If he has spent less time with her, so that the risk of sperm warfare is greater, he needs more killers and egg-getters. So he ships in more of each column. The number of blockers stays the same, but he introduces more of the younger sperm, the killers and egg-getters.
