Sperm Wars: The Science of Sex

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.

Full article: http://findarticles.com/p/articles/mi_m2372/is_n1_v35/ai_20746731/pg_1

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Category: Fertility, Male Fertility, sperm