Sperm Wars

by Robin Baker

  The woman stirred in her post-coital sleep as a familiar sensation began to tickle her buttocks. She opened her eyes and looked at the luminous red numbers on her bedside clock. It was nearly forty-five minutes since her partner had ejaculated inside her. Now she felt the first hint of wetness emerging from her vagina. As she hovered between sleep and consciousness, she tried to decide whether to get up and go to the toilet, to reach for a tissue, or simply to let the familiar liquid ooze out of her vagina, dribble down between her buttocks, and wet the sheet.

  During half-consciousness, her mind drifted back seven years to her first semester as a student. At the beginning of her final long schoolgirl summer, she had met a male college student, two years older than her. Within days of meeting they had sex and thereafter did so whenever the opportunity presented itself. At first they had used condoms, but eventually she had agreed to go on the pill. When summer was over and they had each gone to their separate colleges, they had, for a few months, continued their relationship, taking it in turns at weekends to visit each other in their tiny flats. On such weekends, they always spent the Sunday afternoon in bed having sex. Invariably, they would stay in bed until the very last moment. Then there would be a mad scramble to dress and get to the station in time to catch the last train. Whenever she was returning from visiting him she could guarantee that no sooner would she have just settled comfortably in her seat than she would begin to feel the fruits of their intercourse seeping out on to her knickers. She would then spend the rest of the journey with a clammy sensation between her legs.

  Now, seven years later, lying in bed, she stirred into wakefulness. With great effort she got out of bed, made her way unsteadily to the toilet, switched on the light, sat down and urinated. As she stood up to flush the cistern she looked down into the bowl. There, in the water, were four white, almost spherical globules. It crossed her sleepy mind as she went back to bed that maybe she hadn’t yet conceived because she had a problem retaining sperm. However, no sooner had the thought come than it had gone, and within a minute of lying down she was asleep. Tonight, at least, the sheet had remained dry.

  There are probably few aspects of sex as misunderstood and maligned as the ‘flowback’, that collection of material that flows back out of the vagina sometime after intercourse. To most people it is an irritation and to some even a worry, a threat to their fertility.

  The flowback is a joint man-woman production. The main part is the seminal fluid introduced by the man, almost all of which is ejected from the vagina. To this the woman adds a quantity of mucus from her cervix. There are also cells from the inside of the vagina, dislodged by the thrusting of the penis. But the most common cells in the flowback are the sperm – and there are usually millions of them. From the human perspective, it is difficult to see the flowback as anything other than a negative, passive event. At first sight it might seem an impossible transformation of image to convert a damp patch on the sheet or a dribble down the leg into a positive, dynamic event. Yet that is just what I want to try to do. I want to argue that the flowback is one of a woman’s major weapons in her pursuit of reproductive success.

  One of my favourite photographs of recent years is of a family of zebra: a stallion, a mare and a young foal. The stallion has just inseminated the mare and is still standing on his hind legs, his front legs on her back. The foal is looking the other way, seemingly embarrassed to watch, as its mother ejects from her vagina a dramatic gush of flowback. In zebra, within minutes of insemination, the mare promptly ejects a major part of the stallion’s ejaculate. Women are not as blatant as female zebra, and it might seem that a dribble down the leg can hardly compare with the zebra’s vigorous response. But as part of my research I have had to take a closer interest in flowbacks than perhaps most people, and I can report that women need not, actually, feel at all inferior in this respect.

  The woman in Scene 3 noticed white globules in the toilet after she had urinated. If you are female, try using a mirror to watch the flowback emerge when you urinate about thirty to forty-five minutes after intercourse. You can’t do this on a toilet, so instead try urinating into an empty bath. Crouch down. Separate your pubic hairs and vulval lips so that the urine will squirt forward. Choose your moment. Wait until you can feel that the flowback is gathering, then urinate. Viewing it from the side you will see that the urine stream shoots forward out of the urethra while, a centimetre or so lower down, when the correct muscles contract, the flowback is squirted out of the vagina with impressive force. (If you are male, see if you can persuade your partner to let you watch her eject the flowback.) Whether you are male or female, you will be left in very little doubt that the flowback is the female’s ejection of part of the inseminate that she has just received from the male.

  Women and zebra are not the only two female animals able to do this. Monkeys, rabbits, mice, sparrows – and probably all other female mammals and birds – also eject a flowback.

  How do females do it? Before I can explain what happens in humans, I need to do two things. First, I need to describe in some detail the architecture of a woman’s reproductive tract. Secondly, I need to describe what happens to the ejaculate in that critical first half-hour or so after insemination. These descriptions will take some time.

  Imagine that you are a doctor and that you are just about to give the woman on the bed in front of you an internal examination. She is lying on her back. First, you part any pubic hair that is in the way and separate the main lips so that you can see the entrance to her vagina. The chamber just inside is the vestibule. If your eyesight is good and you separate the vulval lips well enough you will see, opening into the top of the vestibule, the urethra through which she urinates.

  Next, you slip two fingers between the vulval lips into her vagina and gently push them as far as they will go. First, note that the vagina is in contact with your fingers all the way round. This is because, when there is nothing inside it, the vagina is not a tunnel but a slit, with the two walls pressed together. And not only is the vagina not a tunnel, it is not even a throughway. The popular image of it as a tube leading straight into the womb through the cervix is quite wrong. It is also quite wrong to imagine that dead-eye dicks can actually shoot their ejaculate through the cervix straight into the womb. Both of these images are false because the vagina is, in fact, a dead-end. Of course, there is an exit into the womb, but it is not straight ahead; to find that exit requires virtually a right-angled turn.

  Without withdrawing your fingers, turn your hand so that its back is on the bed and your palm is facing upwards. The womb, which is pear-shaped, is balanced on top of the far end of the vagina, probably just beyond your fingertips. The narrow end of the pear is the cervix and it is the cervix that penetrates the roof of the vagina, projecting through by a couple of centimetres. If your fingers are long enough – many aren’t – their tips can feel the cervix sticking through the vaginal roof. The cervix has a narrow channel running though it, and it is this channel which connects the vagina to the inside of the womb and through which the sperm must pass on their way in. It is also through this channel that, in a phenomenal feat of engineering and elasticity, a baby must pass on its way out. For the moment, though, let’s concentrate on the narrowness of the channel and on sperm going in.

  The channel through the cervix is not empty. It is filled with mucus and, if you leave your fingers inside this woman long enough, some cervical mucus will flow out on to them. This is the woman’s main contribution to the flowback and it has a starring role in this book. To understand much of human sexuality, we need to appreciate the beauty of a woman’s mucus and the amazing things she does with it. She has complex requirements of her cervical mucus. On the one hand, it is her last defence against the bacteria and other disease organisms which are forever trying to invade her cervix and womb. On the other hand, she needs it to allow passage to sperm on their way in and to her menstrual flow on its way out. In other words, she needs it to function as a two-way filter.
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br />   Most people think of mucus rather contemptuously as a messy, amorphous substance, probably because their main contact is with the mucus that comes out of their noses. Cervical mucus may look and feel like nose mucus, but it is in fact very different. It is wonderful stuff with an immaculate structure and is absolutely vital to a woman’s health, safety – and sexual power. It contains fibres and is permeated by channels. Most of these channels are very narrow, some only the width of two sperm heads side by side, but they are none the less the highways through which sperm swim as they migrate from the vagina to the inner regions of the cervix and beyond.

  Cervical mucus is secreted continuously, primarily by glands in the top half of the cervix, furthest from the vagina. After being secreted, it slowly flows in glacier-like fashion down through the cervix, eventually dripping into the vagina. The rate of flow of this cervical glacier is slow compared with the speed of a swimming sperm but fast compared with the speed of invading disease organisms. Bacterial and other invaders are carried out of the cervix back into the vagina before they can take hold. In the vagina, they are killed by the acidity of the vaginal juices. During menstruation, the menstrual flow simply adds to the mucus flow. The double flow makes it even more difficult for disease organisms to invade – especially important because during menstruation the raw lining to the womb makes it particularly vulnerable.

  The demands that women make on their cervical mucus are particularly great because of their strategy of copulating when they would seem to have little use for sperm. We have already discussed why women have sex at infertile stages of their menstrual cycle (Scene 2) – to confuse men. Post-menopausal women also copulate to confuse men, often continuing to be sexually active for many years after their last period. By preventing a partner from identifying the end of her reproductive life with certainty, a post-menopausal woman is able to reduce the chances of being deserted for a younger, more fertile woman. In fact, women who are apparently post-menopausal can occasionally conceive – at least up to the age of fifty-seven and reportedly up to the age of seventy (Scene 34). Even pregnant women continue to copulate – again to confuse men, but for particular reasons that we shall discuss in connection with Scene 17.

  At all times, a woman has to balance the advantages of letting sperm through and keeping disease organisms out. Clearly, making life easier for sperm makes it easier for disease organisms too. During pregnancy, a woman has no use for the sperm she collects during copulation, and she ejects the whole inseminate in her flowback; her cervical filter makes life impossible for sperm in order to maximise her defence against disease. At all times other than during pregnancy, however, a sexually active woman may have some use for sperm, and she then needs to sacrifice some of her defence against disease in order to allow sperm through. And just as the advantage of allowing sperm passage varies over the span of her life and during her menstrual cycle, so too does the strength of her cervical filter.

  A non-pregnant woman has least use for sperm during the sub-fertile phases of her life (such as during most of each menstrual cycle and after the menopause). Even during these phases, though, she gains some benefit from allowing sperm passage, because sperm allowed through during a sub-fertile phase can influence the sperm present at the beginning of any next fertile phase (as we shall first see in Scene 7). But since the advantage of retaining sperm during sub-fertile phases is relatively small, a woman can afford to make her cervical filter more hostile to sperm in order to increase her defence against infection. At the approach of ovulation, the advantage of allowing more sperm through her cervix naturally increases, so she makes things as easy as possible for sperm at this time. The way she facilitates or impedes sperm passage during fertile and sub-fertile phases is by altering the nature of the cervical mucus.

  Throughout a woman’s many and long infertile phases, cervical mucus is made difficult to penetrate. The narrow mucus channels are small in number, and although sperm can enter the mucus, few can swim through it. Even those that can penetrate do so more slowly. During this phase the flow of mucus is slow, but fast enough to do its job of combating disease. In contrast, during her short fertile phases, the mucus changes: it becomes much more liquid and stretchy and the channels become bigger. It is more easily invaded by both sperm and bacteria.

  The only major problem faced by invading sperm during a woman’s fertile phases is that not all channels are clear of the blockages referred to earlier. To remove these, and to combat the increased risk of infection, the woman increases the flow rate of her mucus. This way she flushes out cells, bacteria and other debris. She is aware of being wet more of the time and a clear, sweet-smelling secretion appears on her underwear.

  Although the benefit of these changes in the cervical mucus is clear, they could create a problem. They could threaten a woman’s attempts to hide her fertile phase from both her partner and herself (Scene 2). Her body overcomes this threat by making the increase in mucus secretion more erratic and more spread out than would be necessary just to aid the passage of sperm through her cervix. The mucus symptoms can occur more than a week before ovulation and can continue for two or more days afterwards. Consequently, although cervical mucus gives some clue as to the timing of a woman’s fertile phase, it is too unpredictable to ruin her overall strategy.

  So, cervical mucus is an adequate sperm filter in its own right. And no matter what the phase of her menstrual cycle, a woman can enhance the mucus’s filtering efficiency by blocking the channels. The more channels she blocks, the stronger the filter. So what does she use to block her mucus channels? There are three things. One is the blood, tissue and other debris from menstruation. Another is white blood cells (Scene 4). And the third is sperm (Scene 7). These blocks may last for several days but are eventually lost when they are carried inexorably by the cervical glacier of mucus into the vagina. Later, we shall see that this ability of a woman to enhance, or not to enhance, her cervical filter is a most powerful weapon in her attempts to outsmart men (Scenes 22 to 26).

  Even once it is in the vagina, the mucus’s job is not finished. It flows down the walls of the vagina, coating them with a thin film. Some exits, contributing to the ‘wetness’ a woman feels on her vaginal lips. Much of the mucus film, however, remains on her vaginal walls – representing advance preparation for her next intercourse, even if it does not happen for days. When she eventually becomes aroused during foreplay, her vaginal walls begin to ‘sweat’. The sweat itself is not slippery. But when it mixes with the film of old cervical mucus, the result is a very effective lubricant. The vagina is now ready for penetration and intercourse.

  We now have all the information necessary to follow the events that take place from first penetration of the vagina by a penis to the production of the flowback. But to help us along, we require a change of image from that of the internal medical examination that we have used so far. What I am about to describe was first filmed by strapping a fibre-optic endoscope to the underside of a man’s penis just before he and his partner had sex. This gave a penis’s-eye view of what happened; so, to help me in my description, suppose that you have volunteered to take part in such an experiment. You are having intercourse in the missionary position and your erect penis (if you are male) or your partner’s (if you are female) has a camera on its tip. You can see what is being filmed on a big TV screen on the wall in front of you.

  As the penis pushes forward into the vagina for the first time, the vagina walls part and, when the penis is fully in, you can see the blind end of the vagina some distance ahead. Still slightly ahead, sticking through the vagina’s roof, is the cervix. At the moment, with its central, dimple-like opening, it looks like a pink sea anemone shorn of its tentacles. But it will change as intercourse proceeds.

  If you watch the screen when thrusting begins, you will see that each time the penis pulls back the vagina walls close behind it. Each time the penis pushes forward, the walls part. Whenever the penis is fully inserted, you can see the end wall of the vagina
and the protruding cervix. As thrusting continues, the picture at full insertion changes. The far end of the vagina becomes more like a chamber, slowly filling with air and becoming slippery with mucus. Even more dramatically, the cervix begins to stretch and hang down more and more. Gradually it looks less and less like a sea anemone and more and more like a pink, rather broad, elephant’s trunk. Eventually, all you see in front of the fully inserted penis is the front wall of the cervical trunk. Its opening points down to the vaginal floor and cannot really be seen. Towards the climax of intercourse, the cervical opening may even rest on the vaginal floor. When the penis ejaculates, the spurts of semen hit the front wall of the cervix and run down on to the floor of the vagina, forming a pool at the bottom of the chamber. Hanging down, dipped into this pool of semen, for all the world like an elephant’s trunk at a watering hole, is the cervix.

  After a minute or so, with ejaculation complete, the penis begins to shrink. As it does so, the vaginal walls close behind it, helping it out but keeping the pool of semen in. With the shrinking of the penis, we lose our camera-bearer and our TV screen goes dark. However, by now it doesn’t matter much – although critical events are taking place, these are chemical and microscopic rather than obvious.

  The first thing that happens – and we might almost have seen this on our TV screen just before the penis shrank too far down the vagina – is that the seminal pool coagulates, becoming slightly less watery and slightly more jelly-like. The second thing that happens is that sperm start to migrate out of the seminal pool. Their destination is the cervical channel, which they can enter only by passing through the interface which forms between the cervical mucus and the semen. Imagine that the cervix really is an elephant’s trunk, dipping into a large pool of semen. The trunk is full of mucus. This mucus, however, does not dissolve in or even mix with the semen when the two come into contact. Instead, something much more structured takes place.