Eventually, all you see in front of the fully mixes with the film of old cervical mucus, the result is a very inserted penis is the front wall of the cervical trunk. Its opening effective lubricant. The vagina is now ready for penetration and points down to the vaginal floor and cannot really be seen.
Towards the climax of intercourse, the cervical opening may even We now have all the information necessary to follow the rest on the vaginal floor. When the penis ejaculates, the spurts of events that take place from first penetration of the vagina by a semen hit the front wall of the cervix and run down on to the floor penis to the production of the flowback. But to help us along, we of the vagina, forming a pool at the bottom of the chamber. What I am about to like an elephant's trunk at a watering hole, is the cervix.
As it does so, the vaginal walls close behind sex. With the ripples begin to massage the mixture of old semen, mucus, sperm shrinking of the penis, we lose our camera-bearer and our TV and other cells down the vagina. Eventually, the mixture collects screen goes dark. However, by now it doesn't matter much — in the vestibule. On average, this happens about half an hour after although critical events are taking place, these are chemical and ejaculation, but can occur as soon as ten minutes or as long as two microscopic rather than obvious.
Before this, a woman can stand up, walk around, even The first thing that happens — and we might almost have seen urinate, and she will not eject the flowback. Once the flowback this on our TV screen just before the penis shrank too far down the has collected in the vestibule, however, any one of these activities, vagina — is that the seminal pool coagulates, becoming slightly or even a cough or sneeze, will rid her of the unwanted material.
The second thing that Even if she stays asleep, the flowback becomes so liquid after happens is that sperm start to migrate out of the seminal pool. Imagine that the cervix really is an have been introduced — sometimes more, sometimes less.
How elephant's trunk, dipping into a large pool of semen. The trunk is many depends in part on the severity of the woman's cervical full of mucus. This mucus, however, does not dissolve in or even filter. Quite often about one in ten occasions the filler is so mix with the semen when the two come into contact.
Instead, severe that she ejects almost all of the inseminate; more rarely, her something much more structured takes place. Most important of all, The interface between mucus and semen at the mouth of the the proportion of sperm that she keeps It not due to simple chance.
They penetrate a just her cervical filter. Each time she has sex, a woman's body short distance into the cervical trunk, stretching upwards into the decides how many sperm to keep and how many to eject. How mucus like the fingers of a rubber glove. Sperm frantically swim and why, we shall see later. It won't be long before this female into these fingers, and from there stream into the narrower ability becomes very important in the lives of our couple. But not channels of the mucus, leaving the seminal fluid behind.
Later we just yet. After a few minutes dipped into the seminal pool, the cervical trunk begins to shrink back to the roof of the vagina, metamorphosing once more from elephant's trunk to sea anemone. It loses contact with the seminal pool and hence cuts off the upwards escape route for the sperm. Once the cervix has withdrawn, those sperm still in the pool are condemned to ejection and an early death.
About fifteen minutes after ejaculation, the pool begins to decoagulate and becomes more watery again. Our story will be one of men's bodies forever trying to make the best of a bad job, while the woman's body outsmarts and outmanoeuvres them at almost every turn.
But this at first sight uninspiring scene does give us an Scene 4 opportunity to watch men doing something fairly impressive.
A man may not look particularly sophisticated at the moment of Topping Up ejaculation, but something remarkable is, in fact, taking place.
Each time he has intercourse during routine sex, he introduces no Over the next two weeks the couple became quite active, sexually. How does such The coolness of the woman's fertile week evaporated. Both restraint help him in his pursuit of reproductive success? To partners went through a phase of anticipating and enjoying their understand what the man is trying to do, we have to follow further sexual activity more than they had for about a year.
After making those sperm we last saw swimming through the channels in the up on the Saturday night, they had sex twice on the Sunday, once woman's cervical mucus. Half an hour later, they even tried again. He through her cervix into the womb. Except when she is pregnant, had an impressive erection but, despite ten minutes of intermittent her womb is roughly pear-sized as well as pear-shaped.
As with thrusting and encouragement, he eventually had to accept that he the vagina, the walls press closely together, so there is little space wasn't going to ejaculate.
Then they missed a few days. Once in the womb, sperm swim close to the walls and are Wednesday night was the woman's weekly night out with helped by the womb to reach its top, the widest part of the pear: in girlfriends; Thursday night the man's weekly night out 'with the effect, they surf-board, carried on the crests of muscular ripples boys'.
On both nights, when the reveller eventually crawled into passing along the womb's walls. At the top of the womb on each bed, the partner was asleep, or at least pretending to be. On Friday side where horns would be if the pear shape of the womb were a night, however, they had sex and did so again on both Saturday bull's face is the opening to a narrow tube, the oviduct. Although and Sunday. The next week followed a similar pattern, until the there are two oviducts, only one will contain an egg during any woman's period began on the Saturday morning.
Then they given menstrual cycle. Once out of the womb, the sperm swim a abstained until the following Saturday, by which time her short distance along an oviduct until they reach a rest area. Here menstrual bleeding had finished. Back in the cervical mucus, another set of sperm swim along more diagonal channels and stream into tiny crypts in the wall of F ew couples have their routine sex at absolutely fixed intervals. In the four weeks we have been following this couple, they have had penetrative sex ten times and the woman the cervix.
These sperm also, once in the crypts, cease swimming, settle down, and conserve their energy. Over the next four to five days they will gradually wake up and re-enter the cervical has been inseminated nine times. But the time interval from one channel. Then they, too, will complete their journey through the intercourse to the next has varied from as short as thirty minutes mucus, surf-board through the womb, and head for the rest area in albeit without ejaculation or seven hours with ejaculation to as the oviducts.
The final set of sperm simply stay in the cervical mucus. Eventually they die ensure a continuous passage of fresh sperm to the rest areas in — or are killed. Their lethal assailants are the marauding hordes of the oviducts. If he injects more sperm than are needed, they white blood cells which are unleashed by the female from the walls will be wasted; the reservoirs will overflow and even more of her womb within minutes of insemination.
As they advance sperm will simply hang around in the cervical mucus and fall through the cervical mucus, these killer cells engulf and digest live prey to the female's white cells. There is also a danger that too and dead sperm alike.
At their peak the white blood cells can many sperm will arrive in the oviduct and, with a surfeit of the match the numbers of sperm, but within twenty-four hours of chemicals that they carry on their heads Scene 7 , actually insemination these hordes have gone, leaving behind much smaller kill any egg that may be present.
On the other hand, if the man numbers to complete the mopping-up operation. Multitudinous doesn't fill the reservoirs enough, too few sperm will arrive in though the white cells may be, they do not pursue sperm into the the oviduct or the reservoirs will dry up prematurely.
The cervical crypts. Of these, the woman will eject about million in the reservoirs. This he seems to do with remarkable precision.
A few hundred sperm may go straight to the oviducts The adjustments we are talking about are roughly as and about a million may first go into the cervical crypts to form follows. If more than a week has passed since the man last reservoirs, leaving in order to complete their journey to the inseminated his partner, her reservoirs will be empty and he oviducts over the next five days.
In all, about twenty thousand will introduce a full load of sperm, say four hundred million. Of these, perhaps just over a million will fill the reservoirs. If The remainder, those not ejected in the flowback, clutter up the the gap is only three days, he will introduce about two cervical mucus, eventually to be mopped up by white cells or hundred million, and half a million will top up the half-empty carried by the slow, glacier-like flow of the cervical mucus Scene reservoirs.
If the gap is only three hours, he will introduce 3 back into the vagina. Even after half an hour, he may find it difficult million sperm when only about a million enter reservoirs. But all is to ejaculate, like the man in our scene. His body is effectively not what it seems. As far as topping up the woman is concerned, saying that there is no point.
His partner's reservoirs are full the important point is that the size of the reservoirs depends on and any sperm ejaculated will simply be wasted. If he puts in only two Our couple have had penetrative sex ten times in the four hundred million, then the reservoirs will be only half as full as if he weeks we have watched them.
In that time, about three put in four hundred million. So precise is the man's ability to top up his partner that them to produce a steady passage of fresh sperm through each if they had doubled their rate of intercourse, or if they had oviduct over a period of about five days. This traffic probably halved it, it would have made scarcely any difference to the peaks about one to two days after insemination, then gradually total number of sperm she would have received.
This is where topping up comes in. If the male can keep the top up their partner. How do they do it? To answer this, we reservoirs of sperm in the cervical crypts topped up, he can need to understand more about both the architecture of the male reproductive tract and the mechanics of ejaculation. Each sperm will then spend a man is standing in front of you waiting to be examined. His genitals further two weeks queuing in the epididymis and up to a further five are at your eye level.
Note his navel, his pubic hair, and the penis days or so in the vas deferens. There is a little queue-jumping as hanging down, slightly askew, in front of the scrotal sac containing some young sperm from the back of the queue are shunted ahead his pair of testes. Hold his flaccid penis in the palm of your right of older sperm at the front, but this need not concern us here.
Now, let's follow what happens to our medical model as he goes The rather swollen knob at the end of the penis is called the glans off with his two columns of sperm and has intercourse.
While he and, right in front of you, is the vertical, slit-like opening of the was standing in front of you he had no sperm in his urethra, but two urethra. Through this, the man both urinates and ejaculates. Fix sperm tubes containing in total up to about a thousand million the line of his urethra in your mind.
It runs in a straight line from the sperm. Nothing will change when his penis becomes erect, not opening slit, back through the penis shaft, into his body and up to even during the early stages of penetration and thrusting.
Fix your eyes at the top of his pubic hair and Eventually, though, sperm will be shunted out of each sperm tube imagine you can see inside to where the urethra and the bladder and into the urethra. A round sphincter that normally prevents urine join. Just below this point, the urethra is joined from left and right leaking out of the bladder also prevents sperm from entering the by two tubes.
These tubes run all the way down to the testes and bladder. The man's urethra is now loaded, ready to fire. Where these While loading, the man will feel a pleasurable urgency at the base tubes join the urethra, they are surrounded by a walnut-sized mass of his penis. He will also know that ejaculation is imminent. This is the prostate gland, which produces the bulk of the how imminent is, to a limited extent, under his conscious control.
When he finally ejaculates, seminal fluid pours from his prostate So where do these two columns of sperm come from? Even as into his urethra. Then muscles contract and the mixture of fluid and the man stands in front of you, his testes are a hive of activity.
By the time the sperm are mature and fit to be ejaculated, Now, it is not difficult to understand how the man's body controls they have already been herded into the single column of sperm the number of sperm he ejaculates. Depending on how many of his from their testis.
They are in the sperm tube, but they are still in, or loading muscles work, and how strongly, he can shunt any length rather on the surface of, the testis. The sperm tube changes in of each of his sperm columns out of their tubes and into his character along its length: in the testis the tube is called the urethra. Even after loading, his body can change its mind. By epididymis, and from the testis up to the urethra it is called the vas varying the number of spurts, usually from between three and deferens.
Whereas the vas deferens is more or less straight, the eight, he can ejaculate a different proportion of the loaded sperm. Any sperm and seminal fluid left in his urethra after ejaculation can Once the sperm are in the epididymis they are, in effect, simply be flushed out at the next urination. Each time the man ejaculates some Of course, somewhere there needs to be a link between the of his sperm, the rest shunt forward. As part of the front of each man's brain, which keeps track of when he last inseminated his queue is lost through ejaculation, newly mature sperm join the partner, and his genital musculature.
Given such a link, it is not back of the queue in the testis. Slowly he had begun to enjoy himself. Nobody suggests, of course, that a man has conscious control They weren't very practised at having sex with her on top, and a over sperm number. In the midst of thrusting and at the point of couple of times he had slipped out.
She had had to work quite loading his urethra, he does not ask himself consciously, 'Is this a hard but eventually he had ejaculated. Tonight, they had tried the hundred-million occasion or a four-hundred-million? When the Eventually, they had reverted to their usual missionary routine.
This leaves his conscious mind free to that would change her life for ever. She had ovulated Wilier that concentrate on his thrusting — and the woman. As it arrived in the fertilisation zone, three fertile sperm arrived simultaneously. They began to burrow through the outer layers of the egg.
Two of Scene 5 them were delayed for a few seconds as they bumped into each other, attempting to penetrate the same point in the egg's defences. Conception The prize of fertilisation went to the third sperm, which had a clear run, unhindered by any others. By the time another sperm It is Friday night and twenty-one days have passed since the arrived only a few seconds later, the egg had put up its barriers beginning of her last period — bleeding that signalled a second!
The egg had been fertilised by the first month without conception. Briefly, the couple had feared: for sperm to get through. Three months after giving up contraception, their fertility. They were calmed, however, both by the the woman had conceived. Two hundred and fifty days after that medical investigation.
With these reassurances, they had put the she would give birth. The identity of the father, however, would month behind them and started afresh. Now, they have just had never be known. For the sperm waiting in her oviduct that Friday sex and are drifting off into post-coital sleep. Tonight, she won't night had in fact been from two different men. In the past two weeks, their sex life had more or less followed the routine they had established since giving up contraception.
Sex on Saturday, Sunday and sometimes, as this week, also on Friday had become the norm. This week, though, had been T here is one final phase to the odyssey of fertilisation — a phase that can be critical in a man's and a woman's pursuit of reproductive success. On Wednesday night, as soon as she had got In previous scenes, we have followed sperm from their earliest into bed after returning from her weekly night out, she had life in the testes to the moment they are shot into the woman's stroked his body until he awoke and had played with his penis vagina.
We have watched them attempt to escape from the until he was erect. Then, she had sat astride him and manhandled seminal pool, migrate through the narrow channels of cervical his penis into her vagina. There we left them, waiting for the final stage of their layer, the zona, which is the outer membrane of the egg itself. Under the zona is a narrow space which surrounds the final, most Sperm may rest in an oviduct for as long as a day and, at any vulnerable barrier, the vitelline membrane.
One Using its head, the sperm hacks its way through the cumulus by one, they wake up and swim further along the oviduct. Their cells. If successful, and it reaches the zona beneath, it sticks the initial destination is a region in which, if an egg is present, side of its head on to the membrane with chemicals. With this fertilisation can occur. But usually no egg is present, and the chemical attachment serving as an initial purchase, the sperm sperm simply pass through and eventually die.
The behaviour. Its tail starts to beat more vigorously and, once it lashing tail provides the force to push the sperm forwards. Finally, arrives, it often swims frantically in circles or figures of eight. At if this sperm is the first to get through the zona, cross the any one time, the fertilisation zone may contain anything from underlying space and touch the vitelline membrane, it is engulfed one or two to up to a thousand sperm, all looking for the egg that by the egg in a welcoming embrace.
Having embraced one sperm, usually never comes. After a while, they leave the zone, one by the egg passes a chemical message across its surface and, within one. As each leaves, its place is taken by a new, fresher arrival seconds, becomes impenetrable. If you are a human sperm, there from the rest area.
Having left the fertilisation zone, each sperm is no prize for coming second. This then travels to fuse with manage because the end of her oviduct gapes open, its opening the similar heart of the egg.
Fusion of the DNA from sperm and surrounded by finger-like projections. A new person has been conceived, with A short distance away from the end of each oviduct, suspended characteristics that are a subtle mixture of his or her two parents. Tiny We know with certainty the mother of the child in our scene.
As we saw, in those few critical days before towards the black hole of the oviduct. Like a waiting hand, the she ovulated the woman had collected sperm from two men — her finger-like projections funnel the egg into the tube.
From here, the partner and her lover. To see what happened, and to work out who egg begins its five-day journey down towards the womb. We are about to To achieve fertilisation, a sperm has to do more than simply witness a sperm war. The outer line of defence, the cumulus, is a thick layer of shapeless cells which the egg has brought with it from the ovary. Now, however, meeting him out of the blue, many of her old feelings returned. All the same, HI the end of the evening she rejoined her group.
At lunchtime the next day, he turned up at her work and took Sperm Wars her out for a snatched bar lunch. Over lunch, they arranged to meet for a meal that evening. As it was Thursday and her partner would be out with his friends, she reasoned there was no need or point in telling him. As far as she was concerned, the evening SCENE 6 would be totally innocent and therefore not worth mentioning anyway. Even so, she took her ex-boyfriend to a restaurant some A Chance Affair way out of town where they were unlikely to Be seen.
All through the evening, it was obvious he was expecting them The woman was out on her Wednesday night ritual with eight of to end up in bed back at his hotel. He was very attentive and her girlfriends. She had been going out like this for over a year. But the thought of infidelity never seriously crossed her every week. Typically, their night centred on lots of drinking and mind. She still found him attractive and his touches arousing, but talking, a meal and sometimes a club.
Occasionally, a man or two she also found his expectation of sex irritating, almost offensive. As a result, she had long cool phases inwards him throughout the They expected each other from time to time to talk to, and perhaps evening. Eventually, he got the message and backed off. On the even leave with, a man. Even though most of them had a male return journey to her home they simply exchanged pleasantries.
She surprised herself Tonight, it was her turn. Quite by chance, who should walk when a sudden feeling of warmth, nostalgia and maybe guilt into the bar but the man she had met during her last schoolgirl prompted her to kiss him briefly on the cheek. She surprised summer — the one who, for a few months, had been her weekend herself even more when she kissed him again, this time on the sexual partner during her first term as a student.
They recognised lips. Somewhat flustered by this momentary surge of passion, she each other immediately and spent virtually the whole evening got quickly out of the car, wished him a good life, and went talking, catching up on events since their last, rather acrimonious, inside. She learned that he now worked at the other end of the When her partner returned home an hour later, she was in bed country but was in town for a week on business, staying in a pretending to be asleep.
As he fell into a drunken sleep and began nearby hotel. Now nearly thirty, he was still not living with a night of snoring, her thoughts and dreams raced around with the anybody, but had a girlfriend — or two. At some unknown He still oozed masculinity, promiscuity — and unreliability. After that, her nerve failed and she didn't try again that day. On All the next day, at work, she couldn't believe how easy it had Wednesday morning, her mood changed from fear and guilt to all been.
She had spent the evening, albeit quite innocently, with one of calm confidence. Why shouldn't she see him again? He another man, and absolutely no one had known about it. The was an old friend and this could be her last opportunity. After man, their evening, their conversation and their kiss, as well as all, their previous evening together had been innocent enough — memories of their earlier sex life when she was still a teenager, there was no need to feel guilty or nervous.
But maybe there was were at the back of her mind continually as she worked. Her no need to tell anyone, either. He was pleased excitement.
Her knickers were damp virtually all day and on one and surprised to hear from her but was in a hurry and, without visit to the toilet she masturbated. She agreed, and spent the rest of the day did both on Saturday and on Sunday. On Saturday night she in a state of high excitement. She told her friends at work that more or less insisted that he gave her an orgasm before entering she had to visit her sister, and so would not be with them at their her.
It was rare for her to climax during intercourse itself. She weekly get-together. She told her partner, as she left him at never expected to and on the occasions when she really wanted seven o'clock, that she felt like going on to a club and so might an orgasm she made sure it was during foreplay. On Sunday be late. He complained, but not much. However, even floor.
During each orgasm over the weekend, even during before they had finished their first drink at the hotel bar, it was foreplay, the fantasy in her mind was not of her partner it never as if they were students again. The last six years apart had never was these days! Tonight, her mood and behaviour were quite different with her ex-boyfriend. After another drink she sat with her All weekend, she secretly relished her burst of sexual activity knees touching his, and as the conversation flowed touched him and excitement.
At no point, however, did she ever contemplate frequently on his leg or arm with her open hand. When he doing anything more dangerous than fantasise about illicit sex. Her the cold', she readily agreed. After eating, he 'just had to go up to ex-boyfriend was leaving on Thursday and she might never see his room' to get a photograph to show her.
She went with him him again. An idea began to form in her mind and her because she had 'always wanted to see what the rooms were like excitement slowly turned to nervousness. Maybe she should see in this hotel'. It would be easy to arrange. Instead of He never did show her the photograph. Within moments of going out with her friends on Wednesday night, she could spend closing the door they were kissing and removing each other's the evening with him.
All she had to do was pick up the phone, call his clothes. Almost before she could take a breath they were naked mobile, and arrange it. She had been The thought both excited and frightened her, so much so that taken aback by his urgency but made no attempt to slow him all day Monday she did nothing but relish it.
On Tuesday down. Her vagina had been wet with The next day, her ex-boyfriend left for home. They were never anticipation all day and as she walked into his room it had been to see each other again. The day after that she ovulated and in full flow.
Penetration had been quick and easy and ejaculation conceived. Over the next three weeks, she and her partner had had been swift. By the time she discovered her When it was over he apologised, saying that his urgency was pregnancy, her night of infidelity had become a distant memory.
He promised that if they got off the floor and into bed he it had never happened. She gradually convinced herself that the would make it up to her. And he did. For half an hour he baby was in fact her partner's. After all, she'd had sex with him caressed and played with her body with an understanding of her about sixteen times that month compared with that single night womanhood that her partner had never shown.
After she with her ex-boyfriend. Then they Nine months later she was to have a daughter. Two years after began all over again. He still 1 penetrated her early, but this time that, she and her partner had a son, followed three years later by his urgency had gone. Thrusting was slow and long. Unusually another daughter. As the elder daughter grew she came to look for her, she climaxed during thrusting, just a few seconds before more and more like her mother. She also became noticeably he ejaculated.
However, the differences between them tranquillity did not last for long. For the first time that night, seemed no greater than between many brothers and sisters. It was getting late In the years to come, the woman's partner never once Quickly, her fear became all-consuming. She had to get home. Even some excuse for not going home. But she would not hear of it. Eventually, she escaped from his bed body over those few critical days.
Neither of them was ever to on the pretext of going to the toilet. Then she refused to return know that the tiny sperm that entered her egg to produce her first and began to get dressed. Conversation became tense and forced. She even became irritable with him and their parting was an awkward affair. As she taxied home, her flowback seeped on to her knickers in a replay of past times. But she did not notice. Her mind was too full of what she should do when she got home. Quietly, so as not to wake her partner, she undressed, washed T he two scenes 6 and 7 in this short chapter explore first the promotion and then the process of sperm warfare.
In act, only one of these scenes involves people — the one we herself thoroughly, then got into bed. Then she set about waking have just witnessed. Scene 7 is not really a scene at all. As a and arousing him. When he was erect, even before he was fully description of sperm wars in action, it is the only occasion in this awake, she sat astride him, inserted his penis, and after a while book in which it was more appropriate to combine scene with managed to get him to ejaculate inside her.
He dimly registered interpretation. The concentrated instead on enjoying an intercourse without effort. We should note in then on the following Wednesday.
She took one opportunity, passing the unreliable, promiscuous masculinity of the woman's Mil not the other. The Thursday evening had been instigated by ex-boyfriend and that his child showed certain more positive her ex-boyfriend and the woman was in an infertile phase of her characteristics than the children the woman had with her partner.
Her body found barely any attraction in sex with this man. We should also note the number and timing of her orgasms, both Her coolness that evening had kept him at arm's length, even male-induced and via self-stimulation. We will discuss later the though he was manifestly hoping for sex. On the Wednesday, significance of these elements. Here, we concentrate on the however, her mood was quite different.
As she moved into her infidelity itself and on the factors which led the ex-boyfriend's fertile phase on the Monday, the idea of seeing her ex-boyfriend sperm, rather than the partner's, to achieve fertilisation. Clearly, began to appeal to her. Her motivation to do something about it, the outcome had a major impact on the reproductive success of however, did not peak until the Wednesday.
Unknown to all three characters in the scene. The same is not true language were very different from the previous Thursday. Most for infidelity. A woman is much more likely to have penetrative of the leading suggestions still came from the man, but whereas sex with a man other than her partner during her fertile phase. In his bedroom, she cooperated using contraception on such occasions. She accepted In order for these patterns for infidelity to be detected penetration and ejaculation with the minimum of foreplay, and statistically, women must have cycles of mood and behaviour ignored the question of contraception completely.
Later, her that promote them. This book was released on 06 October with total page pages. Book excerpt: This classic work on the rules of sex -- updated for a new generation -- is still as provocative as the day it was published, providing simple explanations for any and all questions about what happens in the bedroom. Sex isn't as complicated as we make it. In Sperm Wars, evolutionary biologist Robin Baker argues that every question about human sexuality can be explained by one simple thing: sperm warfare.
Sasha Dall. Nina Wedell. A short summary of this paper. Download Download PDF. Translate PDF. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately. Dispatch R Med.
Rosenbaum, J. Blacque, O. McCarthy, J. Cell Biol. Piperno, G. Genes Dev. Segil, M. Cole, D. Distinct mutants of retrograde Beech, P. This means that such hermaphrodite: the sea slug Chelidonura hirundinina.
On the other Sasha R. Dall and Nina Wedell coordinating with each other to hand, with less investment in each develop bodies to lionesses potential reproductive event, Conflicts of interest abound in synchronizing their hunts to take males can attempt many more biology.
Indeed, from a neo- large savannah ungulates — matings, but they face the Darwinian, gene selectionist achieving such cooperation problem of winning rights to the perspective many biological presents problems. To enjoy a limited opportunities to access phenomena owe their existence to common good, individuals must the choosy females and their rare the evolutionary outcome of often take on the risk of investing eggs.
This divergent interests in the mating reproductive lineages. Consider sets up the potential to free-ride game, with males being selected genomic imprinting, for instance, — accept resources from the to coerce their partners into whereby genes inherited from pool without investing anything in reproducing and females to resist fathers show different patterns of return.
It is the risk of being such overtures [6]. Nevertheless, despite more than their fair share of the In fact, the burden of explanation such divergence in interests and maternal investment. This is often falls on those instances mating tactics, at least some because such selfishness is where the tragedy of the degree of coordination between unlikely to impact negatively on commons seems to have been the sexes is required to achieve the success of other copies of the averted in biology.
One example the common good of successful genes, as the mother of a current of this is the case of achieving sexual reproduction. For the vast offspring is also likely to invest in the benefits of sexual majority of sexual taxa with offspring sired by other males.
But this is consistent with the available reported in this issue of Current is not necessarily the case in data on patterns of expression of Biology [5]. Chelidonura via desertion had not been hirundinina. The new study by A A single individual; and Anthes et al. One of the major stumbling blocks to providing unequivocal evidence of conditional reciprocity in sperm trading by simultaneous hermaphrodites has been the ability to distinguish punishment by desertion from the termination of mating interactions for other reasons.
This is where cephalaspid sea slugs such as C. By cauterising this sperm groove, Anthes et al.
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