Sperm competition wife

Sperm competition wife DEFAULT

Wife sharing (or cuckolding) is one of the most common fantasies among men and it turns out it may actually increase a woman's ability to get pregnant by creating sperm competition syndrome. In fact, it's how to increase chances of pregnancy, and if done correctly, it won't create an incredible amount of friction in your marriage or relationship.

Sperm competition is actually a term used to define the process of fertilizing a woman's egg with sperm from two or more people. This type of competition usually occurs when a woman is interested in a wife sharing relationship with multiple male partners, which increases the chance of conceiving a child from the variety of mates. Some women begin sexual relationships with multiple mates if her partner is not potent enough to produce children.

Research shows that sperm count increases considerably in men who share their wives sexually with others.

This intense sexual pleasure is be enjoyed by the people who are interested in cuckolding relationship. The feeling of sexual enhancement encourages competition (sperm competition syndrome) between the two or more individuals having sex with the same woman in the wife sharing relationship.

The pressure from sperm competition syndrome compels men to allow their wife or partner to have multiple male mates in order to produce children successfully. The internal process resembles a raffle: the man with more tickets (sperm) has a higher chance of winning (getting the woman pregnant).

But the success in sperm competition depends solely upon the potential of the man to produce sperm in large quantities, which is not easy. On the other hand, the overuse of sharing sperm with many women (in order to increase chances of pregnancy) can reduce their number of sperm.

If it were possible for men to produce sperm at a faster rate to fertilize a woman's egg (and win the raffle), there would be no need to enter into a wife sharing relationship.

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For more information about sperm competition, check out the video below:

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Mike Hatcher writes about open relationships, swinging and sex, and relationship advice for alternative sex lives.

Sours: https://www.yourtango.com/experts/mr-mike-hatcher/sperm-competition-syndrome-wife-sharing-and-hotwifing

Want a baby? Stay away from the wife

Forget wearing loose underpants and romantic candle-lit dinners. Scientists have discovered a simple way of helping couples to conceive: spend more time apart.

Men's sperm count in Britain has been declining rapidly in recent years, leading to fertility problems. But researchers have discovered that men's fertility levels double when they spend most of their time away from their partners.

A report in the scientific journal Personality and Individual Differences says a man's sperm count varies significantly depending on how much he sees his partner. The researchers found that when couples spend all their time together men inseminate 389 million sperm per ejaculation. But when only 5 per cent of their time is in each other's company, the figure almost doubles to 712m.

The report suggests it is not only a case of absence making the heart grow fonder, or of the testicles being replenished with sperm because they haven't been emptied.

It claims there is an evolutionary reason for the surge in fertility: it's the best way a man can ensure his genes win out if his partner has been unfaithful while he was away. By producing so many more sperm while away, a man increases the odds of crowding out a competing man's sperm when he returns.

The researchers say this supports the theory of 'sperm competition', an evolutionary response to humans not being naturally monogamous.

Fertility research has found that, at the time of conception, 4 per cent of women have sperm from different men in their reproductive system. One recent study suggested that one in seven men wasn't the biological father of who he thought was his child. There is also evidence that men produce two types of sperm - one to fertilise the egg, and another to fight off sperm from other males.

The journal report claims women were unfaithful to their long-term partners to maximise chances of becoming pregnant.

Females were likely to indulge in 'short-term mating' with other partners if sex with a regular partner was infrequent.

'An ancestral woman married to a man uninterested in sex may have had a more difficult time getting pregnant,' the report states. 'If this is correct, then fertility back-up is a possible function of a woman's short-term mating. Alternatively, a partner's lack of sexual interest may signal to the woman that he is channelling his sexual interest and perhaps commitment elsewhere, in which case the woman might benefit by doing likewise.' The theory of 'sperm competition' helps to explain the size of testicles across different species. In primates, there is a strong correlation between the size of testicles - and thus the amount of sperm produced - and the level of female promiscuity. The greater the promiscuity, the larger the testicles relative to body size. According to the theory, the males with the biggest testicles are more likely to have offspring, because they produce more sperm, which are more likely to crowd out the sperm of any rival male. Male gorillas can have small testicles and small amounts of sperm because the female of the species is highly monogamous. But chimpanzees are highly promiscuous and the males tend to have testicles relatively 10 times the size of those of gorillas.

Human males are somewhere between chimps and gorillas. This suggests ancestral humans were not as promiscuous as chimpanzees - but neither were they entirely monogamous.

Dr Amin Gorgy, clinical director of the London Fertility Centre, said: 'The bottom line is that it is an interesting theory, but it has not been proven, and I would think it is unlikely to change the cultural behaviour of human beings. However, some men find it difficult to stay monogamous, and maybe there is a biological reason for that.'

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Sours: https://www.theguardian.com/uk/2000/mar/19/anthonybrowne.theobserver
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Author and blogger Chris Ryan guest hosted the Savage Love sex advice column this week. It's a great read, and a wonderful plug for Ryan's new book, Sex at Dawn.

The first letter he answered was from a woman whose husband wanted to watch her have sex with another man, a request she fulfilled. But as she described the enjoyment her husband had at watching her and having "after" sex with her, with the other man's ejaculate inside her, the wife became concerned that maybe her husband was gay.

Ryan and Savage's responses normalized the desire and behavior, suggesting that the husband was heterosexual, and was driven by the biological impetus of sperm competition, and voyeurism.

I like Ryan's responses, especially the nonpathological view, but I also think that this is a very complex behavior, with a lot more reasons behind it.

So I thought I would use this post to explore these issues. Even though the practice of wife-sharing focuses on the wife's sexuality, in my experience, this is almost always prompted by a husband's request. Wives simply do not often or unprompted go to their husbands and request permission to have sex with other men.

In the research for my book, I heard lots of varied reasons for this desire. Some were nice, and some were not so nice, but a discussion of this phenomenon deserves consideration of all the reasons and motivations.

So here is my list of the motivations, based upon my research, behind why men would be interested in watching their wives with other men:

  • Voyeurism. Many suggest that we live in a "pornified culture," where most men of college-age and older have seen pornography, and use it as a part of their sexual repertoire. If they are used to such a voyeuristic process in their sexuality, there is some legitimacy to suggesting they may incorporate it into their marital sexuality. Watching your wife have sex with another man may be a next step, or progression, from watching yourselves have sex by having a mirror on the ceiling, then using a video camera during sex, and finally watching one's spouse with someone else. Many men told me, "My wife is the most beautiful woman in the world to me. I'd rather watch her having sex than some porn actress I don't know."
  • Sperm competition. As Christopher Ryan, author Terry Gould, and researchers Baker and Bellis have suggested, there is a biological response playing out here, one that affects a male sexual drive. After watching their wife with another man, the husband is prompted biologically to have longer, more vigorous sex, has a shorter refractory period between erections, ejaculates harder, and his ejaculate contains more sperm. Nearly every couple I interviewed told me that after an episode of the wife having sex with another man, the couple felt like they were "in heat."
  • The thrill of the taboo. There are few things in our society as stigmatized as a husband whose wife is unfaithful. Historically, such men have been beaten, ostracized, and ridiculed, and regarded as weak, "sissy men." Some of the men I interviewed described explicitly that the taboo was the thrill for them, from the excitement of the forbidden and the naughty.
  • Female empowerment. I was surprised by how many of these couples embraced powerful feminist principles, and how many husbands described the joy they felt at their wife's increased independence, confidence, and assertiveness, coming from her freedom to have sex with other men. Many of the men expressed that through their wife's open sexuality, the couple was actively and consciously rejecting social pressures to suppress female sexuality, assert monogamy and patriarchal power.
  • Bisexuality. For more than half of the men I interviewed, male bisexuality played a role in the husband's desire to watch his wife have sex with another man. This played out in different dynamics. Sometimes, bringing a man to bed with the wife was a pretext—a bait and switch if you will—for the husband to then engage sexually with the man as well. Sometimes, the husbands were very concerned about being seen as heterosexual, but they spent an awful lot of time looking for well-endowed men for their wives. To my mind, a man who is that focused on the size of other men's penises really doesn't qualify as all that straight.
  • Physical health issues. In Lady Chatterley's Lover, Lord Chatterley was physically unable to have intercourse with his wife (though as my own wife points out, his fingers and tongue still worked just fine; why wasn't he using them?). I did see a number of men who reported that due to physical complaints, they weren't able to be as vigorous in bed as they and their wives would like. While the wives, by and large, were happy with things as they were, the husbands often felt their wives ' loss of sexual satisfaction more strongly than the wife themselves and were motivated to encourage the wife to sleep with other men.
  • Female sexual fulfillment. Women's sexual capacity is far greater than that of males'. The world record for male orgasms is about 26 in a 24-hour period. Per Sherfey's research, women have documented as many as 60-65 orgasms in a single hour. I saw many men who reported that their wives were highly sexual beings, with a greater sexual capacity, and it simply turned the husbands on and pleased them to be able to see their wives sexually satisfied, to a degree that a single husband couldn't match. I also speculate that there is a degree of vicarious experience here: By being a part of the experience, the husband gets to vicariously experience what it's like to have that greater sexual capacity and identifies in a strong manner with his wife and the essence of female sexuality in a way that most men never experience.
  • Masochism. Leopold von Sacher-Masoch was a 19th-century fan of flagellation who wrote Venus in Furs about dominant women. Masochism was named after him. Leopold posted ads in German newspapers of the day, looking for "energetic young men" to befriend and pleasure his wife. (Check out Craigslist for Leopold's modern counterparts.) Leopold's interest in the experience was specifically the humiliation aspect—being cuckolded, treated as weak, lesser, and not a real man. Like those who seek the taboo, these cuckolds often seek out a strong SM flavor, in which the husbands are dominated, belittled, and degraded.
  • Financial reasons. Most of the women working in Nevada's brothels have husbands and boyfriends at home, who benefit from the wife's sexual exploits for pay. It's not always about the money. A wife interviewed for my first book told me that when she was working as a manager at a brothel, one of the women always called her husband on her cellphone before bringing a man back to her room for a "party." Unbeknownst to that man, her husband was getting off listening in on the phone. The financial part is a piece that can't be ignored, as it has been around for a long time. In England, men would sometimes set up their wives to be seduced by a man, so that the husband could then sue the man in court. In Florida, in the 1990s, the sheriff husband of the "Housewife Hooker" hid in the closet videotaping his "nymphomaniac wife" with other men (notably Republican politicians), whom he then blackmailed.
  • The royalty perk. In the 1960s Motown song, the line goes "save the last dance for me," as the husband watches his wife dance with other men. Many of the men I interviewed got a thrill, a sense of being "king" that they had a wife who was so sexy that other men wanted to be with, but who ultimately came home with him, the husband. It made the men feel powerful and successful that they had such a sexy wife.
  • Misogyny. Sadly, I saw some couples in which the husband's encouragement of the wife to have sex with other men was about degrading the woman. Some of these men talked about treating the wife as a whore, as a piece of meat, and "taking her down a peg."

A common fantasy is that the practice of wife-sharing starts when a husband catches his wife cheating, and finds himself strangely turned on. This might happen sometimes, though very, very rarely. But it is at the root of Dan Savage's past responses to these men, a response that he and Ryan didn't repeat in this column. Usually, Savage quotes the "eroticization of fear" hypothesis, that these men so fear their wife's infidelity that they eroticize the fear, in order to reduce the anxiety, managing it by sexuality, until they have turned the fear into a sexual fetish. In my book, I encountered a single man who described this scenario. It might happen, but it's a lesser answer than all of the above. Hopefully through their partnership, Christopher Ryan opened Savage's eyes to the wide range of other explanations.

Facebook image: Artem Oleshko/Shutterstock

Sours: https://www.psychologytoday.com/us/blog/women-who-stray/201007/why-would-you-do-watch-your-wife-another-man
Human Sperm Competition Theory

Human sperm competition

Sperm competition is a form of post-copulatory sexual selection[1] whereby male ejaculates simultaneously physically compete to fertilize a single ovum.[2] Sperm competition occurs between sperm from two or more rival males when they make an attempt to fertilize a female within a sufficiently short period of time.[3] This results primarily as a consequence of polyandrousmating systems, or due to extra-pair copulations of females, which increases the chance of cuckoldry, in which the male mate raises a child that is not genetically related to him.[1][3][4] Sperm competition among males has resulted in numerous physiological and psychological adaptations, including the relative size of testes, the size of the sperm midpiece, prudent sperm allocation, and behaviors relating to sexual coercion,[1][3][4][5] however this is not without consequences: the production of large amounts of sperm is costly[6][7] and therefore, researchers have predicted that males will produce larger amounts of semen when there is a perceived or known increase in sperm competition risk.[3][7]

Sperm competition is not exclusive to humans, and has been studied extensively in other primates,[5][8][9] as well as throughout much of the animal kingdom.[10][11][12] The differing rates of sperm competition among other primates indicates that sperm competition is highest in primates with multi-male breeding systems, and lowest in primates with single-male breeding systems.[5][8] Compared to other animals, and primates in particular, humans show low-to-intermediate levels of sperm competition, suggesting that humans have a history of little selection pressure for sperm competition.[5]

Physiological adaptations to sperm competition[edit]

Physiological evidence, including testis size relative to body weight and the volume of sperm in ejaculations, suggests that humans have experienced a low-to-intermediate level of selection pressure for sperm competition in our evolutionary history.[4][5] Nevertheless, there is a large body of research that explores the physiological adaptations males do have for sperm competition.[3]

Testis size and body weight[edit]

Evidence suggests that, among the great apes, relative testis size is associated with the breeding system of each primate species.[13] In humans, testis size relative to body weight is intermediate between monogamous primates (such as gorillas) and promiscuous primates (such as chimpanzees), indicating an evolutionary history of moderate selection pressures for sperm competition.[4]

Ejaculate volume[edit]

The volume of sperm in ejaculates scales proportionately with testis size and, consistent with the intermediate weight of human males testis, ejaculate volume is also intermediate between primates with high and low levels of sperm competition.[4] Human males, like other animals, exhibit prudent sperm allocation, a physiological response to the high cost of sperm production as it relates to the actual or perceived risk of sperm competition at each insemination.[14] In situations where the risk of sperm competition is higher, males will allocate more energy to producing higher ejaculate volumes.[14] Studies have found that the volume of sperm does vary between ejaculates,[15] and that sperm produced during copulatory ejaculations are of a higher quality (younger, more motile, etc.) than those sperm produced during masturbatory ejaculates or nocturnal emissions.[3] This suggests that, at least within males, there is evidence of allocation of higher quality sperm production for copulatory purposes. Researchers have suggested that males produce more and higher quality sperm after spending time apart from their partners, implying that males are responding to an increased risk of sperm competition,[16] although this view has been challenged in recent years. It is also possible that males may be producing larger volumes of sperm in response to actions from their partners, or it may be that males who produce larger volumes of sperm may be more likely to spend more time away from their partners.[3]

Size of sperm midpiece[edit]

Diagram of human sperm cell

The size of the sperm midpiece is determined in part by the volume of mitochondria in the sperm.[17] Sperm midpiece size is tied to sperm competition in that individuals with a larger midpiece will have more mitochondria, and will thus have more highly motile sperm than those with a lower volume of mitochondria.[17] Among humans, as with relative testis size and ejaculate volume, the size of the sperm midpiece is small compared to other primates, and is most similar in size to that of primates with low levels of sperm competition, supporting the theory that humans have had an evolutionary history of intermediate levels of sperm competition.[5]

Penis anatomy[edit]

Several features of the anatomy of the human penis are proposed to serve as adaptations to sperm competition, including the length of the penis and the shape of the penile head. By weight, the relative penis size of human males is similar to that of chimpanzees, although the overall length of the human penis is the largest among primates.[18] It has been suggested by some authors that penis size is constrained by the size of the female reproductive tract (which, in turn is likely constrained by the availability of space in the female body), and that longer penises may have an advantage in depositing semen closer to the female cervix.[19] Other studies have suggested that over our evolutionary history, the penis would have been conspicuous without clothing, and may have evolved its increased size due to female preference for longer penises.[20]

The shape of the glans and coronal ridge of the penis may function to displace semen from rival males, although displacement of semen is only observed when the penis is inserted a minimum of 75% of its length into the vagina.[21] After allegations of female infidelity or separation from their partner, both men and women report that men thrusted the penis more deeply and more quickly into the vagina at the couple's next copulation.[21]

Psychological adaptations to sperm competition[edit]

In addition to physiological adaptations to sperm competition, men also have been shown to have psychological adaptations, including certain copulatory behaviors, behaviors relating to sexual coercion, investment in relationships, sexual arousal, performance of oral sex, and mate choice.

Copulatory behaviors[edit]

Human males have several physiological adaptations that have evolved in response to pressures from sperm competition, such as the size and shape of the penis.[21] In addition to the anatomy of male sex organs, men have several evolved copulatory behaviors that are proposed to displace rival male semen. For example, males who are at a higher risk of sperm competition (defined as having female partners with high reproductive value, such as being younger and physically attractive) engaged more frequently in semen-displacing behaviors during sexual intercourse than men who were at a lower risk of sperm competition.[22] These semen-displacing behaviors include deeper and quicker thrusts, increased duration of intercourse, and an increased number of thrusts.[21][22]

Sexual coercion and relationship investment[edit]

Men who are more invested into a relationship have more to lose if their female partner is engaging in extra-pair copulations.[3] This has led to the development of the cuckoldry risk hypothesis, which states that men who are at a higher risk of sperm competition due to female partner infidelity are more likely to sexually coerce their partners through threatening termination of the relationship, making their partners feel obligated to have sex, and other emotional manipulations of their partners, in addition to physically forcing partners to have sex.[23] In forensic cases, it has been found that men who rape their partners experienced cuckoldry risk prior to raping their partners.[24] Additionally, men who spend more time away from their partners are not only more likely to sexually coerce their partners, but they are also more likely to report that their partner is more attractive (as well as reporting that other men find her more attractive), in addition to reporting a greater interest in engaging in intercourse with her.[25] Men who perceive that their female partners spend time with other men also are more likely to report that she is more interested in copulating with him.[25]

Sexual arousal and sexual fantasies[edit]

Sperm competition has also been proposed to influence men’s sexual fantasies and arousal. Some researchers have found that much pornography contains scenarios with high sperm competition, and it is more common to find pornography depicting one woman with multiple men than it is to find pornography depicting one man with multiple women,[26] although this may be confounded by the fact that it is less expensive to hire male pornographic actors than female actors.[27] Kilgallon and Simmons documented that men produce a higher percentage of motile sperm in their ejaculates after viewing sexually explicit images of two men and one woman (a sperm competition risk) than after viewing sexually explicit images of three women, likely indicating a response to an active risk of sperm competition.[28]

Oral sex[edit]

It is unknown whether or not men’s willingness and desire to perform oral sex on their female partners is an adaptation.[3] Oral sex is not unique to humans,[29][30][31] and it is proposed to serve a number of purposes relating to sperm competition risk. Some researchers have proposed that oral sex may serve to assess the reproductive health of a female partner[32] and her fertility status,[33] to increase her arousal, thereby reducing the likelihood of her having extra-pair copulations,[34] to increase the arousal of the male to increase his semen quality, and thereby increase the likelihood of insemination,[35] or to detect the presence of semen of other males in the vagina.[32][36]

Mate choice[edit]

Sperm competition risk also influences males' choice of female partners. Men prefer to have as low of a sperm competition risk as possible, and they therefore tend to choose short-term sexual partners who are not in a sexual relationship with other men.[3] Women who are perceived as the most desirable short-term sexual partners are those who are not in a committed relationship and who also do not have casual sexual partners, while women who are in a committed long-term relationship are the least desirable partners.[37] Following the above, women who are at an intermediate risk of sperm competition, that is women who are not in a long-term relationship but who do engage in short-term mating or have casual sexual partners, are considered intermediate in desirability for short-term sexual partners.[37]

Effects of sperm competition on human mating strategies[edit]

High levels of sperm competition among the great apes are generally seen among species with polyandrous (multimale) mating systems, while lower rates of competition are seen in species with monogamous or polygynous (multifemale) mating systems.[4][5][38] Humans have low to intermediate levels of sperm competition, as seen by humans’ intermediate relative testis size, ejaculate volume, and sperm midpiece size, compared with other primates.[4][5] This suggests that there has been a relatively high degree of monogamous or polygynous behavior throughout our evolutionary history.[38] Additionally, the lack of a baculum in humans[39] suggests a history of monogamous mating systems.

Males have the goal of reducing sperm competition by selecting women who are at low risk for sperm competition as the most ideal mating partners.[37]

Intra-ejaculate sperm competition[edit]

Noticing that sperm in a mixed sample tends to clump together--making it less mobile--and to have a high mortality rate, reproductive biologist Robin Baker, formerly of the University of Manchester, proposed about a decade ago that some mammals, including humans, manufacture "killer" sperm whose only function is to attack foreign spermatozoa, destroying themselves in the process.

To test this idea, reproductive biologist Harry Moore and evolutionary ecologist Tim Birkhead of the University of Sheffield in the U.K. mixed sperm samples from 15 men in various combinations and checked for how the cells moved, clumped together, or developed abnormal shapes. "These are very simple experiments, but we tried to mimic what goes on in the reproductive tract," Moore says. The team found no excess casualties from any particular donor or other evidence of warring sperm, they report in the 7 December Proceedings of the Royal Society. "The kamikaze sperm hypothesis is probably not a mechanism in human sperm competition," says Birkhead.

The findings are "the nail in the coffin for the kamikaze hypothesis," says Michael Bedford, a reproductive biologist at Cornell University's Weill Medical Center in New York City. He says he had never given the idea much credence.  [40]

Female responses to sperm competition[edit]

A survey of 67 studies reporting nonpaternity suggests that for men with high paternity confidence rates of nonpaternity are (excluding studies of unknown methodology) typically 1.9%, substantially less than the typical rates of 10% or higher cited by many researchers.[41] Cuckolded fathers are rare in human populations. "Media and popular scientific literature often claim that many alleged fathers are being cuckolded into raising children that biologically are not their own," said Maarten Larmuseau of KU Leuven in Belgium. "Surprisingly, the estimated rates within human populations are quite low--around 1 or 2 percent." "Reliable data on contemporary populations that have become available over the last decade, mainly as supplementary results of medical studies, don't support the notion that one in 10 people don't know who their "real" fathers are. The findings suggest that any potential advantage of cheating in order to have children that are perhaps better endowed is offset for the majority of women by the potential costs, the researchers say. Those costs likely include spousal aggression, divorce, or reduced paternal investment by the social partner or his relatives. The observed low cuckoldry rates in contemporary and past human populations challenge clearly the well-known idea that women routinely 'shop around' for good genes by engaging in extra-pair copulations to obtain genetic benefits for their children," Larmuseau said. [42]

Women are loyal to men who are good providers. "With DNA tests now widely available, so-called paternity fraud has become a staple of talk shows and TV crime series. Aggrieved men accuse tearful wives who profess their fidelity, only to have their extramarital affairs brought to light...The rule of thumb seems to be that males of higher socioeconomic status, and from more conventionally bourgeois societies, have greater warranted paternity confidence. Lower paternity confidence among those who are the principals for sensational media shouldn’t be surprising then."[43] Five days a week, you can tune into “Paternity Court,” a television show featuring couples embroiled in disputes over fatherhood. It’s entertainment with a very old theme: Uncertainty over paternity goes back a long way in literature. Even Shakespeare and Chaucer cracked wise about cuckolds, who were often depicted wearing horns.

Sperm competition in other primates[edit]

The relative size of human male testes is comparable to those primates who have single-male (monogamous or polygynous) mating systems, such as gorillas and orangutans,[13] while it is smaller when compared to primates with polyandrous mating systems, such as bonobos and chimpanzees.[4][5][13] While it is possible that the large testis size of some primates could be due to seasonal breeding (and consequently a need to fertilize a large number of females in a short period of time), evidence suggests that primate groups with multi-male mating systems have significantly larger testes than do primates groups with single-male mating systems, regardless of whether that species exhibits seasonal breeding.[38] Similarly, primate species with high levels of sperm competition also have larger ejaculate volumes[4] and larger sperm midpieces.[5]

Unlike all other Old World great apes and monkeys, humans do not have a baculum (penile bone). Dixson[44] demonstrated that increased baculum length is associated with primates who live in dispersed groups, while small bacula are found in primates who live in pairs. Those primates that have multi-male mating systems tend to have bacula that are larger in size, in addition to prolongation of post-ejaculatory intromission and larger relative testis size.[21][45]

References[edit]

  1. ^ abcShackelford, Todd K.; Goetz, Aaron T. (2007). "Adaptation to sperm competition in humans". Current Directions in Psychological Science. 16 (1): 47–50. doi:10.1111/j.1467-8721.2007.00473.x. S2CID 6179167.
  2. ^Pham, Michael N.; Shackelford, Todd K. (2014). “Sperm competition and the evolution of human sexuality”. In T.K. Shackelford & R.D. Hansen. The Evolution of Sexuality. Cham: Springer. pp. 257-275. ISBN 9783319093840.
  3. ^ abcdefghijShackelford, Todd K.; Goetz, Aaron T.; LaMunyon, Craig W., Pham, Michael N; Pound, Nicholas. (2016). “Human sperm competition”. In D.M. Buss. The Handbook of Evolutionary Psychology (2nd ed.). New York: Wiley. pp. 427-443. ISBN 9781118755884.
  4. ^ abcdefghiSimmons, Leigh W.; Firman, Renée C.; Rhodes, Gillian; Peters, Marianne. (2004). “Human sperm competition: Testis size, sperm production, and rates of extrapair copulations”. Animal Behaviour.68 (2): 297-302.
  5. ^ abcdefghijMartin, Robert D. (2007). “The evolution of human reproduction: A primatological perspective”. Yearbook of Physical Anthropology.50: 59-84.
  6. ^Dewsbury, Donald A. (1982). “Ejaculate cost and male choice”. The American Naturalist.119 (5): 601-610.
  7. ^ abBaker, R. Robin; Bellis, Mark A. (1993). “Human sperm competition: Ejaculate adjustment by males and the function of masturbation”. Animal Behaviour.46 (5): 861-885.
  8. ^ abMøller, Anders Pape. (1988). “Ejaculate quality, testes size and sperm competition in primates”. Journal of Evolution.17 (5): 479-488.
  9. ^Dixson, A. F. (1987). "Observations on the evolution of the genitalia and copulatory behaviour in male primates". Journal of Zoology. 213 (3): 423–443. doi:10.1111/j.1469-7998.1987.tb03718.x.
  10. ^Parker, G.A. (1970). “Sperm competition and its evolutionary consequences in the insects”. Biological Reviews. 55 (4): 525-567.
  11. ^Birkhead, T.R.; Møller, A.P. (1992). Sperm competition in birds: Evolutionary causes and consequences. London: Academic Press. ISBN 0121005402.
  12. ^Ginsberg, J.R.; Huck, U.W. (1989). “Sperm competition in mammals”. Trends in Ecology and Evolution. 4 (3): 74-79.
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  14. ^ abWedell, Nina; Gage, Matthew J.G.; Parker, Geoffrey A. (2002). “Sperm competition, male prudence, and sperm-limited females”. Trends in Ecology and Evolution. 17 (7): 313-320.
  15. ^Mallidis, C.; Howard, E.J.; Baker, H.W.G. (2008). “Variation of semen quality in normal men”. International Journal of Andrology. 14 (2): 99-107.
  16. ^Baker, R. Robin; Bellis, Mark A. (1989). “Number of sperm in human ejaculates varies in accordance with sperm competition theory”. Animal Behaviour. 37: 867-869.
  17. ^ abAnderson, Matthew J.; Dixson, Alan F. (2002). “Sperm competition: Motility and the midpiece in primates”. Nature. 416 (6880): 496.
  18. ^Short, R.V. (1979). “Sexual selection and its component parts, somatic and genital selection as illustrated by man and the great apes”. Advances in the Study of Behavior. 9: 131-158.
  19. ^Brown, Luther; Shumaker, Robert W.; Downhower, Jerry F. (1995). “Do primates experience sperm competition?” The American Naturalist.146 (2): 302-306.
  20. ^Mautz, Brian S.; Wong, Bob B.M.; Peters, Richard A.; Jennions, Michael D. (2013). “Penis size interacts with body shape and height to influence male attractiveness”. Proceedings of the National Academy of Sciences of the United States. 110 (17): 6925-6930.
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Sours: https://en.wikipedia.org/wiki/Human_sperm_competition

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