Sperm Wars

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Sperm Wars
Original Fourth Estate Cover for Sperm Wars 1996.jpg
Front cover of original 1996 publication
Author Robin Baker [1]
Subjects Sperm competition
Human sexuality
Evolution
Publisher Fourth Estate, London [1]
Publication date
1996 [1]
Publication placeUnited Kingdom [1]
Media typePrint, Paperback [1]
Pages384 [1]
ISBN 978-1-85702-356-5

Sperm Wars is a popular science book by evolutionary biologist Robin Baker about sperm competition. [2] [3] Originally published in English in 1996, it has since appeared in 25 languages [4] and in 2006 a 10th anniversary edition [2] was published in the United States.

Contents

Description

Through a series of short fictional stories and discussion following them, Baker proposes evolutionary functions for sexual habits, mostly on the principle of competition between sperm of different men for a prized egg. [2] The "sperm wars" include both literal battles between sperm inside a woman's reproductive tract, as well as figurative battles between men competing for the chance to mate. The book is controversial, [5] both because of its explanations of homosexuality, sexual assault, and prostitution, and because some critics have claimed that several of the hypotheses in the book are not supported by scientific research.

Oral sex is explained as an opportunity for partners to judge each other's reproductive health, and for mates to detect recent infidelity (also proposed by Kohl & Francoeur, 1995 "The Scent of Eros"). The shape of the penis and the thrusting during intercourse serve to remove other men's semen. [6] Male masturbation is said to discard old, dying sperm, so that an ejaculate contains younger sperm that will stay active inside the cervix longer, with more of a chance of being present during the window of ovulation. Baker also proposes that men adjust the amount of sperm they ejaculate based on the time their mate has spent away from them. [7] Likewise, women are found to be more likely to engage in extra-pair copulation and retain larger amounts of sperm during their most fertile phase of the month, and more likely to have sex with their regular partner during the infertile phase. [8]

Focus

A major focus of the book is sperm heteromorphism, in which not only are a variety of morphological types [9] of sperm apparent in every normal human ejaculate, but also at any one time fewer than 1% seem capable of responding to and fertilizing an egg. [10] A similarly low proportion of fertile sperm is found in the ejaculates of mice. [11] Baker calls these fertile sperm "egg-getters", and claims that the rest of the sperm in the ejaculate are infertile "kamikaze sperm" or "blockers", whose primary purpose is to prevent other men's sperm from getting to the egg. [12] He cites data suggesting that in Britain at least 4% of children (but perhaps as many as 6–12%) are conceived via sperm competition, [13] and claims that this lower figure is consistent with the earlier finding that 10% of children have a biological father who is other than their supposed father. [14] Baker describes in detail how "killer sperm" actively seek out rival sperm and kill them with poison from acrosomes to prevent them from getting to the egg. This literal sperm warfare was not observed in a subsequent experiment, [15] but Baker criticizes the protocol in this latter experiment. [5]

Studies

Based on studies with a fiber optic endoscope attached to a man's penis during sex, Baker describes how the cervix behaves during sex and orgasm, dipping down "like an elephant's trunk" into the pool of semen so that the sperm can more easily swim into it, the so-called "upsuck theory" of female orgasm. This has also come under some criticism; see Cervix#Function. He theorizes about how the timing of orgasm can affect fertility, due to changes in the cervical mucus said to accompany orgasm, which then affect its ability to "filter out" sperm and prevent them from traveling into the cervix. Other studies have found no connection to sperm transport or fertility. [16] [17]

Although Baker draws a clear distinction between predatory rape and date rape, the book has drawn criticism for portraying date rape and "rough-and-tumble intercourse" as being on the same spectrum of behaviour: a test of the male's strength and ability. Despite Baker asserting that the two behaviours are at different (illegal and legal) ends of that spectrum, his statement that the drawing of the line between criminal and non-criminal behaviour is a job for the legal profession and not for the biologist has led some to interpret his words as meaning that he sees no real difference between the two: [18]

Initially, she can simply watch him in competition with other males. ... But finally, the only real test a woman can set is whether a man can negotiate and overcome her own defences. To test this, she has to resist first verbally, then physically. The stronger and more realistic her resistance, the better the test.

In this context he makes comparison with the many examples of aggressively induced ovulation in mammals, including the extreme example of mink in which if the female does not experience physical trauma at the male's hands, she does not ovulate [19] [20]

Orientation

Regarding sexual orientation, he states that true homosexuals are rare; that only 6% of the male population engages in any sort of homosexual behavior in their lifetime, and that 80% of those also have sex with women, so he focuses on bisexuality. "It seems most likely that exclusive homosexuality is a genetic by-product of the reproductively advantageous characteristic of bisexuality. If so, homosexual behaviour joins the ranks of a number of other human characteristics that are advantageous when a person has inherited a few of the relevant genes, but disadvantageous if they have inherited more."

Bisexuality in both men and women is explained as an adaptive trait because it provides earlier opportunities to gain sexual experience, and more opportunities to practice skills such as infidelity and interacting with people of different personalities. Experience gained with a member of the same sex of a particular character type can help the bisexual to get the most out of a relationship with a member of the opposite sex of a similar character type. Although studies show that by the age of 40 years bisexuals have fewer children than heterosexuals, [21] [22] he maintains that at low levels in the population bisexuality is still an evolutionary advantage since the children are typically conceived earlier in life; by age 20 years bisexuals have four times the reproductive success of heterosexuals, and by age 25 twice the success. [23] Homophobia is then explained as a natural response to the threat of this reproductive advantage (despite the fact that true homosexuals are not in competition for females), as well as "the bisexual's role in the spread of disease".

Related Research Articles

Orgasm or sexual climax is the sudden release of accumulated sexual excitement during the sexual response cycle, characterized by intense sexual pleasure resulting in rhythmic, involuntary muscular contractions in the pelvic region. Orgasms are controlled by the involuntary or autonomic nervous system and experienced by both males and females; the body's response includes muscular spasms, a general euphoric sensation, and, frequently, body movements and vocalizations. The period after orgasm is typically a relaxing experience, after the release of the neurohormones oxytocin and prolactin, as well as endorphins.

<span class="mw-page-title-main">Pre-ejaculate</span> Clear fluid emitted from the urethra of the penis during arousal

Pre-ejaculate is a clear, colorless, viscous fluid that is emitted from the urethra of the penis during sexual arousal and in general during sexual activity. It is similar in composition to semen but has distinct chemical differences. The presence of sperm in the fluid is variable from low to absent. Pre-ejaculate functions as a lubricant and an acid neutralizer.

A wet dream, sex dream, or sleep orgasm, is a spontaneous occurrence of sexual arousal during sleep that includes ejaculation and orgasm for a male, and vaginal lubrication and/or orgasm for a female.

<span class="mw-page-title-main">Female reproductive system</span> Reproductive system of female humans

The human female reproductive system is made up of the internal and external sex organs that function in the reproduction of new offspring. The reproductive system is immature at birth and develops at puberty to be able to release matured ova from the ovaries, facilitate their fertilization, and create a protective environment for the developing fetus during pregnancy. The female reproductive tract is made of several connected internal sex organs—the vagina, uterus, and fallopian tubes—and is prone to infections. The vagina allows for sexual intercourse, and is connected to the uterus at the cervix. The uterus accommodates the embryo by developing the uterine lining.

<span class="mw-page-title-main">Sperm competition</span> Reproductive process

Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and variety of mates increases a female's chance to produce more viable offspring. However, multiple mates for a female means each individual male has decreased chances of producing offspring. Sperm competition is an evolutionary pressure on males, and has led to the development of adaptations to increase male's chance of reproductive success. Sperm competition results in a sexual conflict between males and females. Males have evolved several defensive tactics including: mate-guarding, mating plugs, and releasing toxic seminal substances to reduce female re-mating tendencies to cope with sperm competition. Offensive tactics of sperm competition involve direct interference by one male on the reproductive success of another male, for instance by mate guarding or by physically removing another male's sperm prior to mating with a female. For an example, see Gryllus bimaculatus.

Insemination is the introduction of sperm (semen) into a female or hermaphrodite's reproductive system in order to fertilize the ovum through sexual reproduction. The sperm enters into the uterus of a mammal or the oviduct of an oviparous (egg-laying) animal. Female humans and other mammals are inseminated during sexual intercourse or copulation, but can also be inseminated by artificial insemination.

<span class="mw-page-title-main">Anisogamy</span> Sexual reproduction involving a large, female gamete and a small, male gamete

Anisogamy is a form of sexual reproduction that involves the union or fusion of two gametes that differ in size and/or form. The smaller gamete is male, a sperm cell, whereas the larger gamete is female, typically an egg cell. Anisogamy is predominant among multicellular organisms. In both plants and animals, gamete size difference is the fundamental difference between females and males.

<span class="mw-page-title-main">Human reproductive system</span> Organs involved in reproduction

The human reproductive system includes the male reproductive system, which functions to produce and deposit sperm, and the female reproductive system, which functions to produce egg cells and to protect and nourish the fetus until birth. Humans have a high level of sexual differentiation. In addition to differences in nearly every reproductive organ, there are numerous differences in typical secondary sex characteristics.

<span class="mw-page-title-main">Human reproduction</span> Procreative biological processes of humanity

Human reproduction is sexual reproduction that results in human fertilization to produce a human offspring. It typically involves sexual intercourse between a sexually mature human male and female. During sexual intercourse, the interaction between the male and female reproductive systems results in fertilization of the ovum by the sperm to form a zygote. While normal cells contain 46 chromosomes, gamete cells only contain 23 single chromosomes, and it is when these two cells merge into one zygote cell that genetic recombination occurs and the new zygote contains 23 chromosomes from each parent, giving it 46 chromosomes. The zygote then undergoes a defined development process that is known as human embryogenesis, and this starts the typical 9-month gestation period that is followed by childbirth. The fertilization of the ovum may be achieved by artificial insemination methods, which do not involve sexual intercourse. Assisted reproductive technology also exists.

<span class="mw-page-title-main">Sexual conflict</span> Term in evolutionary biology

Sexual conflict or sexual antagonism occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly over the mode and frequency of mating, potentially leading to an evolutionary arms race between males and females. In one example, males may benefit from multiple matings, while multiple matings may harm or endanger females due to the anatomical differences of that species. Sexual conflict underlies the evolutionary distinction between male and female.

<span class="mw-page-title-main">Masturbation</span> Sexual stimulation of ones own genitals

Masturbation is a form of autoeroticism in which a person sexually stimulates their own genitals for sexual arousal or other sexual pleasure, usually to the point of orgasm. Stimulation may involve use of hands, everyday objects, sex toys, or more rarely, the mouth. Masturbation may also be performed with a sex partner, either masturbating together or watching the other partner masturbate.

<span class="mw-page-title-main">Semen quality</span> Measure of male fertility

Semen quality is a measure of male fertility, a measure of the ability of sperm in semen to accomplish fertilization. Semen quality involves both sperm quantity and quality. Semen quality is a major factor for fertility.

<span class="mw-page-title-main">Human penis</span> Human male external reproductive organ

In human anatomy, the penis is an external sex organ through which males urinate and ejaculate. Together with the testes and surrounding structures, the penis functions as part of the male reproductive system.

Human sexuality is the way people experience and express themselves sexually. This involves biological, psychological, physical, erotic, emotional, social, or spiritual feelings and behaviors. Because it is a broad term, which has varied with historical contexts over time, it lacks a precise definition. The biological and physical aspects of sexuality largely concern the human reproductive functions, including the human sexual response cycle.

<span class="mw-page-title-main">Semen</span> Reproductive biofluid of male or hermaphroditic animals

Semen, also known as seminal fluid, is a bodily fluid that contains spermatozoa. Spermatozoa are secreted by the male gonads and other sexual organs of male or hermaphroditic animals and can fertilize the female ovum. In placental mammals, semen also contains secretions from the male accessory glands and is discharged from the penis through the urethral orifice during ejaculation. In humans, seminal fluid contains several components besides spermatozoa: proteolytic and other enzymes as well as fructose are elements of seminal fluid which promote the survival of spermatozoa and provide a medium through which they can move or "swim". The fluid is adapted to be discharged deep into the vagina, so the spermatozoa can pass into the uterus and form a zygote with an egg.

<span class="mw-page-title-main">Ejaculation</span> Semen discharge from the male reproductive tract

Ejaculation is the discharge of semen from the penis through the urethra. It is the final stage and natural objective of male sexual stimulation, and an essential component of natural conception. After forming an erection, many men emit pre-ejaculatory fluid during stimulation prior to ejaculating. Ejaculation involves involuntary contractions of the pelvic floor and is normally linked with orgasm. It is a normal part of male human sexual development.

<span class="mw-page-title-main">Robin Baker (biologist)</span> British novelist, popular science writer, lecturer and broadcaster

Robin Baker is a British novelist, popular science writer, lecturer and broadcaster. A best-selling author in the field of sexual biology his books have been translated into 27 different languages. These include the international bestseller Sperm Wars which was based on his own lab's original research on human sexuality. His work and ideas on the evolution of human behaviour have been featured in many radio and television programmes around the world.

Female copulatory vocalizations, also called female copulation calls or coital vocalizations, are produced by female primates, including human females, and female non-primates. They are not purposeful, but instead are evolutionary and are spontaneously produced by female primates, including women, to encourage her partner to produce good-quality sperm during the mating process. Copulatory vocalizations usually occur during copulation and are hence related to sexual activity. Vocalizations that occur before intercourse, for the purpose of attracting mates, are known as mating calls.

<span class="mw-page-title-main">Non-reproductive sexual behavior in animals</span> Non-reproductive behavior in non-human animals

Animal non-reproductive sexual behavior encompasses sexual activities that non-human animals participate in which do not lead to the reproduction of the species. Although procreation continues to be the primary explanation for sexual behavior in animals, recent observations on animal behavior have given alternative reasons for the engagement in sexual activities by animals. Animals have been observed to engage in sex for social interaction bonding, exchange for significant materials, affection, mentorship pairings, sexual enjoyment, or as demonstration of social rank. Observed non-procreative sexual activities include non-copulatory mounting, oral sex, genital stimulation, anal stimulation, interspecies mating, same-sex sexual interaction, and acts of affection, although it is doubted that they have done this since the beginning of their existence. There have also been observations of sex with cub participants, as well as sex with dead animals.

<span class="mw-page-title-main">Human sperm competition</span> Form of sexual selection

Sperm competition is a form of post-copulatory sexual selection whereby male sperm simultaneously physically compete to fertilize a single ovum. 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. This results primarily as a consequence of polyandrous mating 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. 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, however this is not without consequences: the production of large amounts of sperm is costly 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.

References

  1. 1 2 3 4 5 6 "BookFinder.com: Search Results (Matching Titles)". www.bookfinder.com. Retrieved 21 March 2018.
  2. 1 2 3 Product Description. ASIN   1560258489.
  3. ↑ "Robin Baker". panmacmillan.com. Archived from the original on 6 October 2007. Retrieved 29 December 2009.
  4. ↑ "Sperm Wars - Robin Baker". robin-baker.com. 22 February 2011.
  5. 1 2 "Sperm Wars: controversies and science - Robin Baker". www.robin-baker.com. 6 March 2011.
  6. ↑ Gallup, G.G. & Burch, R.L. (2004) Semen Displacement as a Sperm Competition Strategy in Humans. Evolutionary Psychology, 2, 12–23.
  7. ↑ Baker, R.R. & Bellis, M.A. (1989). Number of sperm in human ejaculates varies in accordance with sperm competition theory. Anim. Behav., 37, 867–869.
  8. ↑ Bellis, M.A. & Baker, R.R. (1990). Do females promote sperm competition?: Data for humans [ dead link ]. Anim. Behav., 40, 997–999.
  9. ↑ Belsey, M.A. et al. (1987) WHO Laboratory Manual for Examination of Human Semen and Semen-Cervical Mucus Interaction. 2nd edn, Cambridge University Press, Cambridge
  10. ↑ Quinn, P. & Marrs, R.P. (1991) Effect of concentration and total number of spermatozoa on fertilizationof human oocytes in vitro. Hum. Reproduc. 6, Suppl. 1, Abst 238
  11. ↑ Siddiquey, A.K.S. & Cohen, J. (1982) In vitro fertilization in the mouse and the relevance of different sperm-egg concentrations and volumes. J. Reprod. Fertil. 66, 237–42
  12. ↑ Baker, R.R. & Bellis, M.A. (1988). ‘Kamikaze’ Sperm in Mammals? [ dead link ] Anim. Behav., 36, 936–939.
  13. ↑ Baker, R.R. & Bellis, M.A. (1995) Human Sperm Competition: copulation, masturbation and infidelity . Chapman & Hall, London. pp.201–2
  14. ↑ Macintyre, S. & Sooman, A. (1992) Non-paternity and prenatal genetic screening. Lancet, 338, 839.
  15. ↑ Moore, H. D. M. (7 December 1999). "No evidence for killer sperm or other selective interactions between human spermatozoa in ejaculates of different males in vitro". Whiterose.ac.uk. 266 (1436): 2343.
  16. ↑ Bancroft, 1989
  17. ↑ Masters & Johnson, 1966
  18. ↑ Sperm Wars: The Science of Sex. - book reviews "Baker makes few distinctions between these two types of aggression and attributes both to female testing of male partners' strength and ability to overcome her resistance"
  19. ↑ Ford, C.S. and Beach, F.A. (1952) Patterns of Sexual Behavior . Eyre and Spottiswoode, London
  20. ↑ Van Tienhoven, A. (1968) Reproductive Physiology of Vertebrates . W.B. Saunders, London.
  21. ↑ Essock-Vitale, S.M. & McGuire, M.T. (1985) Women's lives viewed from an evolutionary perspective: I. Sexual Histories, reproductive success, and demographic characteristics of a random sample of American women. Ethol. Sociobiol., 6, 137–54
  22. ↑ Baker, R.R. & Bellis, M.A. (1995) Human Sperm Competition: copulation, masturbation and infidelity. Chapman & Hall, London. pp.117
  23. ↑ Baker, R.R. & Bellis, M.A. (1995) Human Sperm Competition: copulation, masturbation and infidelity. Chapman & Hall, London. pp.117–8
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