Sperm Wars: The Science of Sex.

By Robin Baker. New York: Basic Books, 1996, 319 pages. Cloth, $25.00.

Reviewed by Michael W. Wiederman, Ph.D., Ball State University, Department of Psychological Science, Muncie, IN 47306.

What would you say if I told you that women influence their fertility through masturbation? That men adjust the number of sperm in each ejaculate according to the relative likelihood that their female partner may have been unfaithful recently? That women are most likely to have sex with an extradyadic partner near the peak of their monthly fertility and are most likely to have sex with their regular sex partner during the infertile phase? Or that the timing of a woman's orgasm within a given sexual episode of coitus influences whether she will become pregnant from that act of intercourse? These are a just a few of the basic biological phenomena upon which the extremely fascinating and revolutionary book, Sperm Wars, is based.

Many readers of JSR may be unfamiliar with the author, Robin Baker, a biologist working in England, whose primary publication outlet for the unique work conducted with colleague Mark Bellis has been the journal, Animal Behavior (Baker & Bellis, 1993a, b; Bellis & Baker, 1990). These earlier empirical articles were based on questionnaire data as well as analyses of hundreds of human ejaculates collected during masturbation and coitus, including many samples of the "flowback" from women's vaginas. Sperm Wars is also based on more recent work in which Baker and Bellis documented what occurs inside the woman's body at the moments of ejaculation and female orgasm using a fiber-optic endoscope attached to the underside of a man's penis. As Baker commented, those images "completely changed my scientific understanding of what happens at the most critical moments during sex" (p. xvii). Sperm Wars has that effect on its readers as well.

The descriptions of what occurs biologically during sexual activity directly challenge many notions we were taught, and may continue to teach to our students, regarding male and female bodily response during and after sexual activity. Even such sacred notions as sperm existing with the "goal" of seeking and fertilizing the prized egg are turned on their head. Baker describes at least three types of distinctly different sperm, each with an apparently different mission. The "egg-getters," those who match our usual characterization of the typical sperm, in actuality comprise only 1% or less of the sperm in a man's ejaculate. Other sperm appear to function as "blockers" of women's cervical crypts or "egg-killers" who attack foreign sperm. Baker also discusses the discovery of specialized sperm that may kill a man's own egg-getters under certain prescribed circumstances. Lest you think that all of this talk of biology results in a "dry" reading experience, realize that Sperm Wars was written for public consumption, and as such does not contain one formal reference, no mention of other researchers, and no subject index. Instead, the author has taken his insights into the biology of sexual behavior, mixed in a fair amount of speculation, and presents the results through 37 narrative "scenes."

Baker notes that he did not intend for the scenes through which various phenomena are characterized to be pornographic or inherently arousing, yet many of them are very explicit and detailed depictions of both typical and atypical sexual behavior. Immediately following each scene, Baker describes what occurred from the perspective of an evolutionary biologist. That is, from an evolutionary and biological view, why did each actor in the scene behave the way he or she did? Why did each actor's body respond the way it did? And what are the reproductive and interpersonal implications of each? Although the underpinnings of the book include evolutionary theory and natural selection, the reader is not sedated with a lengthy treatise of either.

The insights, observations, and speculations are too numerous to catalogue here, but I will present a couple of them, especially those having to do with sexual phenomena that have been problematic for previous authors to explain from a functional or an evolutionary perspective. The nature of the "sperm wars" around which the book is based have to do with both competition among two or more men's sperm within the same woman, as well as a sort of evolutionary "war" that may occur between the male and female within a given sexual dyad. That is, in the latter type of sperm war, a woman's body may be "trying" to avoid conception from a particular insemination, whereas a man's body might be "trying" to achieve fertilization of her egg (in an evolutionary sense of reproductive fitness). Both types of "wars" are highlighted throughout the book, particularly as various sexual behaviors and experiences fit with the goals and outcomes of each type of battle.

For example, why do so many humans find oral sex arousing and a desirable activity? Of course, the simple answer is "it feels good." But beyond the sheer physical stimulation it provides, why is it arousing? Why is oral sex more desirable to many than manual manipulation of the genitals? Baker posits that, in an ultimate sense, providing oral sex offers a unique opportunity to gather (perhaps subconsciously) information about a partner's reproductive health and (possible) recent infidelity. The first type of sperm war mentioned previously had to do with sperm competition among men. Baker admits this sperm competition is relatively rare (he estimates that approximately 20% of conceptions involve such sperm competition), yet the reproductive implications are strong enough to have shaped dramatically men's and women's sexuality, both biological and psychological. Offering a mate the opportunity to perform oral sex at least communicates recent fidelity (or at least nothing to hide in that regard). That is, performing oral sex offers the possibility to detect, through visual, olfactory, and gustatory cues, secretions left behind by a recent interloper (especially relevant data during our evolutionary history in which douches and baths were nonexistent or infrequent). These hypotheses fit well with another recent book that included consideration of the ultimate functions of oral sex (Kohl & Francoeur, 1995). Baker explains how oral sex, both giving and receiving, evolved to become more or less inherently pleasurable because of the ultimate functions it may have served.

Other writers have attempted to explain the function and evolutionary value of female orgasm, and typically concluded that female orgasm is an unintended evolutionary byproduct or evolved to strengthen pairbonds, (e.g., Fisher, 1992; Symons, 1979). Armed with more recent and relevant data, Baker describes how women's orgasms, although certainly not required for fertilization, can profoundly affect likelihood of conception. After describing at length the vaginal and cervical environments, Baker introduces the concept of a "cervical filter," referring to the type and amount of cervical mucus, cellular debris, ejected sperm, and other organic material. The strength of a woman's cervical filter fluctuates depending on various conditions, one of which is length of time since last orgasm. Orgasm (from masturbation, for example) results in a stronger cervical filter if performed 24 hours after intercourse than orgasm experienced 48 hours after intercourse. The strength of the cervical filter affects the relative ease with which sperm can reach the fallopian tubes, where fertilization typically takes place.

The story does not stop there. Through experiments conducted in his lab, Baker found that timing of female orgasm during or around the occurrence of vaginal intercourse further affects the likelihood of fertilization. During female orgasm the woman's cervix dips and the opening to the cervix gapes open, much like an elephant's trunk while taking in water. If a seminal pool is present in the vagina at that point, a significant number of sperm will be helped along by this "up-suck" phenomenon. So, to maximize conception, a woman should experience an orgasm immediately after a man ejaculates. If the woman experiences orgasm when a seminal pool is not present, vaginal secretions are likely to be "sucked up," thereby increasing the acidity of the cervical environment. Accordingly, female orgasm prior to male ejaculation strengthens the cervical filter and reduces the likelihood of fertilization. In this context, Baker also discusses the role of nocturnal orgasms in women's sexuality.

I was fascinated by this and other material in Sperm Wars, yet as I try to convey some of it here I am struck by how sterile the bare information seems. One strength of the book is Baker's ability to weave didactic coverage of material with his narrative scenes in which realistic sexual scenarios are used to provide a context for what the biological phenomena "look like," or actually how they play out, in real life. Accordingly, I encourage the reader of this review not to judge the book by my meager description.

Despite the praise I lavish on Baker and Sperm Wars, the book is not without its flaws and shortcomings. On a very minor note, there are several places where the reader encounters a British use of a word or phrase that an American is not likely to understand fully. On a conceptual level, those involved in the social sciences may feel as though something is missing. Baker's background is biology, so it should not be surprising that the book is weaker in providing psychological links between biological function and overt behavior. As just one example, Baker describes how men adjust the number of sperm in their ejaculate according to the proportion of time since last intercourse during which the man's partner was out of his sight (and hence potentially available for rival insemination). What is missing is an attempted answer to the fascinating questions of what psychological mechanisms are involved in performing such a "calculation" and what other relationship characteristics might affect the adjustment of sperm in ejaculate.

Ultimately, in discussing most phenomena, Baker relies on a sort of anthropomorphic presentation of men's and women's bodies. That is, he translates an ultimate reproductive advantage associated with certain sexual behaviors into a kind of hidden agenda on the part of men's and women's bodies. At times, human bodies are presented as sort of having minds of their own, which frequently result in a "conflict between the conscious brain and the subconscious body" (p. 109). Baker starts with the assumption that "whenever the body is intent upon a particular course of action, it generates an urge to perform that action" (pp. 166-167) and concludes that

most of the strategies shown by

men and women in relation to

ejaculation and orgasm are

subconscious--orchestrated by the

body via sequences of mood, libido,

and sensitivity to stimulation. Indeed,

most of the behavior described

in this book is similarly

subconscious, the product of genetic

programming rather than

cerebral rationalization. (p. 199)

Social scientists more concerned with conscious processes and social forces may be somewhat uncomfortable with these basic assumptions upon which Sperm Wars is based. In a general sense, there is a problem of teleology as Baker frequently seems to jump from the existence of a sexual behavior to its ultimate reproductive function (consequence) to an inherent motivation on the part of the individual engaging in the behavior.

Also, even though Baker explained that it was not his intention nor belief that Sperm Wars contains sexist views (p. xxiv), some very controversial ideas are sure to offend some and anger others. One primary example involves Baker's position on sexual aggression within relationships, from "rough-and-tumble sex play" to forced intercourse. 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. "To test this [ability], she has to resist first verbally, then physically. The stronger and more realistic her resistance, the better the test" (p. 223). Baker notes that "[i]n species such as humans that form long-term relationships, rough-and-tumble sexual behavior is most important during early stages of courtship. Once a woman has tested a man's ability to force himself on her, she need not do it often thereafter" (pp. 223-224). I do not even have to elaborate on the ideological problem many readers would have with this perspective. Empirically, data are needed to support such an interpretation of the reproductive "function" of sexual aggression (playful or otherwise) within couples.

Despite a lack of psychological underpinning and some politically incorrect views, Sperm Wars truly is a revolutionary look at human sexual behavior. Rather than attempting to explain only certain aspects of sexual behavior, or isolated sexual phenomena, Baker bites off large pieces in his attempt to explain human sexuality. From routine sexual functioning, to extradyadic sex, to fantasies and erotica, to masturbation and wet dreams, Baker weaves empirical findings, evolutionary theory, speculation, and narrative illustration into a very readable account. The academic who reads Sperm Wars will not likely swallow everything whole, but I can guarantee that the experience will forever alter how the reader views human sexual behavior.

References

Baker, R. R., & Bellis, M. A. (1993a). Human sperm competition: Ejaculate adjustment by males as a function of masturbation. Animal Behavior, 46, 861-885.

Baker, R. R., & Bellis, M. A. (1993b). Human sperm competition: Ejaculate manipulation by females as a function for the female orgasm. Animal Behavior, 46, 887-909.

Bellis, M. A., & Baker, R. R. (1990). Do females promote sperm competition? Data for humans. Animal Behavior, 40, 997-999.

Fisher, H. (1992). Anatomy of love: The mysteries of mating, marriage, and why we stray. New York: Fawcett Columbine.

Kohl, J. V., & Francoeur, R. T. (1995). The scent of eros: Mysteries of odor in human sexuality. New York: Continuum.

Symons, D. (1979). The evolution of human sexuality. New York: Oxford University Press.