Sperm Wars
Encyclopedia
Sperm Wars is a primarily nonfiction book by evolutionary biologist Robin Baker
. Originally published in English in 1996, it has since appeared in 25 languages and in 2006 a 10th anniversary edition was published in the United States. Through a series of short 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. 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, both because of its explanations of homosexuality
, rape
, and prostitution
, and because some authors 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. 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. 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.
A major focus of the book is sperm heteromorphism
in which not only are a variety of morphological types 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. A similarly low proportion of fertile sperm is found in the ejaculates of mice. 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. He cites data suggesting that in Britain at least 4% of children (but perhaps as many as 6-12%) are conceived via sperm competition, 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. 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, but Baker criticizes the protocol in this latter experiment.
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.
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:
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
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, 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. 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".
Dr Robin Baker
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...
. Originally published in English in 1996, it has since appeared in 25 languages and in 2006 a 10th anniversary edition was published in the United States. Through a series of short stories and discussion following them, Baker proposes evolutionary functions for sexual habits, mostly on the principle of competition between sperm
Sperm competition
Sperm competition is a term used to refer to the competitive process between spermatozoa of two different males to fertilize an egg of a lone female. Competition occurs whenever females engage in promiscuous mating to increase their chances in producing more viable offspring...
of different men for a prized egg. 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, both because of its explanations of homosexuality
Homosexuality
Homosexuality is romantic or sexual attraction or behavior between members of the same sex or gender. As a sexual orientation, homosexuality refers to "an enduring pattern of or disposition to experience sexual, affectional, or romantic attractions" primarily or exclusively to people of the same...
, rape
Rape
Rape is a type of sexual assault usually involving sexual intercourse, which is initiated by one or more persons against another person without that person's consent. The act may be carried out by physical force, coercion, abuse of authority or with a person who is incapable of valid consent. The...
, and prostitution
Prostitution
Prostitution is the act or practice of providing sexual services to another person in return for payment. The person who receives payment for sexual services is called a prostitute and the person who receives such services is known by a multitude of terms, including a "john". Prostitution is one of...
, and because some authors have claimed that several of the hypotheses in the book are not supported by scientific research.
Oral sex
Oral sex
Oral sex is sexual activity involving the stimulation of the genitalia of a sex partner by the use of the mouth, tongue, teeth or throat. Cunnilingus refers to oral sex performed on females while fellatio refer to oral sex performed on males. Anilingus refers to oral stimulation of a person's anus...
is explained as an opportunity for partners to judge each other's reproductive health, and for mates to detect recent infidelity
Infidelity
In many intimate relationships in many cultures there is usually an express or implied expectation of exclusivity, especially in sexual matters. Infidelity most commonly refers to a breach of the expectation of sexual exclusivity.Infidelity can occur in relation to physical intimacy and/or...
(also proposed by Kohl & Francoeur, 1995 "The Scent of Eros"). The shape of the penis
Penis
The penis is a biological feature of male animals including both vertebrates and invertebrates...
and the thrusting during intercourse
Sexual intercourse
Sexual intercourse, also known as copulation or coitus, commonly refers to the act in which a male's penis enters a female's vagina for the purposes of sexual pleasure or reproduction. The entities may be of opposite sexes, or they may be hermaphroditic, as is the case with snails...
serve to remove other men's semen. Male masturbation
Masturbation
Masturbation refers to sexual stimulation of a person's own genitals, usually to the point of orgasm. The stimulation can be performed manually, by use of objects or tools, or by some combination of these methods. Masturbation is a common form of autoeroticism...
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
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...
. Baker also proposes that men adjust the amount of sperm they ejaculate based on the time their mate has spent away from them. 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.
A major focus of the book is sperm heteromorphism
Sperm heteromorphism
Sperm heteromorphism is the simultaneous production of two or more distinguishable types of sperm by a single male. The sperm types might differ in size, shape and/or chromosome complement. Sperm heteromorphism is also called sperm polymorphism or sperm dimorphism . Typically, only one sperm type...
in which not only are a variety of morphological types 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. A similarly low proportion of fertile sperm is found in the ejaculates of mice. Baker calls these fertile sperm "egg-getters", and claims that the rest of the sperm in the ejaculate are infertile "kamikaze
Kamikaze
The were suicide attacks by military aviators from the Empire of Japan against Allied naval vessels in the closing stages of the Pacific campaign of World War II, designed to destroy as many warships as possible....
sperm" or "blockers", whose primary purpose is to prevent other men's sperm from getting to the egg. He cites data suggesting that in Britain at least 4% of children (but perhaps as many as 6-12%) are conceived via sperm competition, 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. 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, but Baker criticizes the protocol in this latter experiment.
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.
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:
In this context he makes comparison with the many examples of aggressively induced ovulation in mammals, including the extreme example of mink
Mink
There are two living species referred to as "mink": the European Mink and the American Mink. The extinct Sea Mink is related to the American Mink, but was much larger. All three species are dark-colored, semi-aquatic, carnivorous mammals of the family Mustelidae, which also includes the weasels and...
in which if the female does not experience physical trauma at the male's hands, she does not ovulate
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
Bisexuality
Bisexuality is sexual behavior or an orientation involving physical or romantic attraction to both males and females, especially with regard to men and women. It is one of the three main classifications of sexual orientation, along with a heterosexual and a homosexual orientation, all a part of the...
. "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, 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. Homophobia
Homophobia
Homophobia is a term used to refer to a range of negative attitudes and feelings towards lesbian, gay and in some cases bisexual, transgender people and behavior, although these are usually covered under other terms such as biphobia and transphobia. Definitions refer to irrational fear, with the...
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".
External links
- Sperm Wars: The Science of Sex. - book reviews (Summary)
- Sex Is Best When You Lose Your Head - on killer sperm and testicle size