Promiscuity

Darwin's evolutionary theory, as originally presented, taught the importance of, and the powerful results of, the processes of sexual selection. However, according to author and professor Tim Birkhead, Darwin's attention stopped short at mate selection. This current work takes the study of sexual selection to yet another level - - to what dynamics are at work during and after copulation.

The author is Professor of Behavioural Ecology at the University of Sheffield (in the Department of Animal and Plant Sciences), and his specific academic focus is on the study of sperm competition in birds. However, in this book he moves deftly and easily into the broader animal world.

Conveniently for the reader, the very first sentence in this book very accurately conveys the book's focus, scope and theme:

In a quite readable and engaging style, Professor Birkhead presents the reader with an enormous amount of detail in a quite palatable manner. From references to the legends (and factual knowledge) of ancient Greeks to charming details about 20^th century theorists, the reader's attention is securely held across the book's seven fast chapters.

The first chapter addresses reproductive competition directly, noting the different strategies inherent in the genders. Both general theoretical considerations are discussed and specific supporting research presented. Most interesting is Birkhead's summary of the recent controversy about the possibility of intravaginal sperm competition in humans. This notion, based on work by Robin Baker and Mark Bellis, was brought to the public's titillated attention by none other than Desmond Morris. The idea is that human sperm comes in a variety of types; one is a sort of "killer sperm" that attacks the sperm of other men, should that sperm be encountered in the reproductive tract of a female. However, Birkhead dissembles this theory by citing subsequent research that failed to support it. "The view of human sperm competition they [Baker and Bellis] have perpetuated is little more than a sexual fantasy - - phallus in wonderland . . ." (p. 29).

Consistent with his engaging style, Birkhead's second chapter begins with the very interesting story of the paternity suit filed by Joan Barry against Charlie Chaplin. This section of the book deals with issues of paternity, generally sticking to non-human species. In almost all species studied, "The single most striking result from the slow accumulation of paternity studies has been the near elimination of the idea of male and female sexual monogamy" (p. 38-39).

The chapter on genitalia (mostly non-human) will astound most readers. In these days of sex education we often overestimate what we know about sexuality. Birkhead elucidates the reader about the reproductive tracts, gonads, and penises of a variety of creatures, and it will be enough here to say that the diversity of the animal kingdom has never seemed so broad. Another especially interesting chapter explores the behaviors surrounding the act of copulation. (Relax! - - again the author sticks primarily to non-human species.)

The last two chapters address the issues of sperm competition and "female choice," i.e., polyandry and female promiscuity. In many species, such as those of various insects, females mate with many different males, and the sperm that produces offspring is not necessarily a "winner" due to random chance. Active research in this area is still going on, but "recently . . . the role of the female in determining the outcome of sperm competition has been taken more seriously" (p. 166). One researcher has identified "at least twenty different ways in which females can modify or control the outcome of copulations with two or more partners" (p. 186).

Regarding the behaviors of our own species, Birkhead points out that "Polyandrous marriages in humans are extremely rare and occur only in cultures where, for ecological or social reasons, resources are extremely limited" (p. 215). (However, recent research suggests that while formal marriages to more than one male are rare, the rate of impregnations via extramarital relations is not insignificant in many cultures.)

In his conclusion, Birkhead writes that in this book he has "tried to address the double-edged question of why sex is a battle" (p. 232). He further notes that we now realize that the two sexes co-evolve, and that therefore "it is not obvious that either sex can ever be a clear winner" (p. 233).

For social scientists, this book will be a rigorous read due to the level of detail and the scope of his biologically oriented approach. However, Birkhead is an excellent, clear writer and this allows even non-biologists to learn much about his subject. Certainly, the book will stimulate the reader to consider the meaning of male-female relationships in a new light.

© 2002 Keith Harris
 

Keith Harris, Ph.D.  is a clinical psychologist and supervisor of Victor Valley Behavioral Health Center in San Bernardino county, California. His interests include clinical supervision, the empirical basis for psychotherapy research (and its design), human decision-making processes, and the shaping of human nature by evolutionary forces.