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:

"This is a book about reproduction. It is about the causes
and consequences of female promiscuity, and in particular the
ways in which the two components of Darwin’s concept of sexual
selection – – competition between males and choice by females
– – operate after insemination has taken place." (p. ix)

(It is worth emphasizing at this point that after the first chapter,
Birkhead turns almost exclusively to the behaviors and tendencies
of non-human animals – – birds, fish, and insects are given prime
billing, although other species are also addressed. Human behaviors
and affairs are, in general, referenced only in passing and indirectly.)

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.

Categories: Genetics

Tags: Behavioral and Cognitive Sciences, Science (General)