Brain Sex by Anne Moir and David Jessel: A Summary

The book Brain Sex describes experiments that have been done to tease out the differences between men and women that result from biology, as opposed to differences that result from culture. The summary below was not written by me (Kenny Felder): it used to be on Wikipedia, but then it was taken down because it is a summary of the book's contents rather than an encyclopedia article about the book. Since I refer to the findings of this book in my essay on feminism, I wanted this summary to still be available, so I have copied it here.

Brain Sex is a popular market book about the biology of gender, the biological differences between men and women, by Anne Moir (geneticist) and David Jessel (journalist), first published by Pearson PLC. The sequence of chapters broadly follows the human life cycle: birth, maturity, reproduction.

Chapter One: The differences

The first chapter of the book establishes the state of the gender debate at the time of publication. It acknowledges that the majority opinion of educated people (at the time of publication) was that men and women have the same brain. However, it claims that this is in stark contrast to the opinion of research scientists in the area. There is a cursory literature review of a century of sex research, featuring some early crude and unreliable results (the book's assessment), but proceeding to the modern results available from about the middle of the 20th century.

Chapter Two: The birth of difference

In chapter two, the authors begin their systematic presentation of the scientific data. It starts by explaining sexual reproduction, the sex determination system and X and Y chromosomes. It extends beyond this to late 20th century discoveries regarding the effects of sex hormones on brain formation in the womb. It gives extended treatment of studies on animals, which show both distinct similarities to and differences from humans. Rat brain structure and consequent behavior can be altered by hormone treatment "after birth" in ways that have not worked with humans. Four case studies of people who were born with intersex physicalities are used to illustrate the effects of hormonal influence on human behavior "prior to birth."

Chapter Three: Sex in the brain

In this chapter, the results regarding a "two-fold" operation of hormones in humans are presented. This is described as an initial morphological influence on the brain during gestation, followed by an "activation" stage at puberty. In other words, hormones have been discovered to be instrumental in shaping initial brain structure; later they stimulate features of these sexual dimorphic brain structures. Hormone activity is not strictly limited to puberty nor to solely reproductive functions.

Brain dimorphism, as observably distinct and complicated as it is, theoretically could be of as little significance for behavior as, for example, eye color. So additional material regarding correlations between brain structure and behavior is actually the main feature of this chapter. Initial studies in this area came from observing people who had suffered brain damage. Correlations between which behavioral functions showed impairment and which regions of the brain showed damage led to early results regarding left and right brain hemisphere activity. Although knowledge of this area is still far from complete, a great deal of refinement has been made possible with brain imaging technology and investment in research projects into human brain function.

One simplification of the results is that female brains (the result of default or "normal" developmental pathways) generally distribute processing across diverse regions of the brain. Male brains (testosterone modified versions of the female brain) are notably more "compartmentalized" and "focused" in their processing. This is the science behind the popular language of women typically having a natural aptitude for "multi-tasking," and men seeming to generally adopt "single minded" behavioral strategies.

Chapter Four: Childhood differences

Chapter four begins with case studies and proceeds through the chronological sub-sections: babies, toddlers, nursery school and school. It is in this section that the superior sensory processing of female brains and the tendency of girls to engage more readily with adults is introduced. Boys, by comparison, do not seem to observe as much, nor have as strong a preference for inter-personal engagement. However, they talk as much (but to themselves or things), and are generally more "active and wakeful." The discussion is illustrated by references to a mother, Gillian, who sought to avoid sexual stereotyping in raising her twins Annie and Andrew, only to find, with frustration, that her children resisted her efforts.

Although the chapter makes the case for objective, universal biological development of sex difference in behavior, it is explicit in noting that socialization is also very much part of behavioral development in general. The first case study in the chapter is Genie, a girl who was raised in isolation and struggled to develop language ability. The point of the chapter is that sexually dimorphic behaviors "include" biological influences that are resistant to socialization, not that all behavior or all dimorphic behaviors are purely biological. As the conclusion of the book makes explicit, its thesis is that purely social explanations of gender are inadequate, not that biological explanations are necessary and sufficient conditions.

Chapter Five: The brains come of age

Structural dimorphism of the brain alone can account for a great deal of the behavioral and other differences between boys and girls. However, the impact of higher levels of sex-specific hormones on the already dimorphic brains leads to even more profound differences between mature men and women. A survey of this phenomenon is the topic of chapter five.

Again this chapter features several case studies. It first considers the influence of female hormones on the behavior of women. The pronounced cyclic rhythm of female hormones, and their widely attested effects, is considered in detail. The case studies are extreme examples. The influence of testosterone on men, especially with regard to aggression, is also noted in this chapter and extends to discussion of higher prevalence of social deviancy among men. Although consideration of the extremes and the negative social impact of hormonal influence occupies the majority of the chapter, it concludes with aspects of dimorphic patterns of behavior that are generally considered socially constructive, even if stereotypical.

Chapter Six: The ability gap

Chapter six considers the statistical differences in performance between men and women, particularly those of children and adolescents in educational environments. Case studies of hormonally atypical children whose performance correlates more closely with children of the other sex is presented.

Although there is evidence for measurable differences in performance of various cognitive and other tasks, the chapter focuses on these as an outcome of preference and strategy. It is not a question of seeking to demonstrate an overall superiority of one sex or the other; rather, the evidence is evaluated for what it appears to support regarding biologically prompted alternative approaches to life challenges.

The point of this is that men and women have preferences, not simply abilities. So external performance based selection of men and women may well lead to more women than men in certain roles (and vice versa). However, the evidence also suggests that men and women are just as likely to learn and pursue specific social roles in different proportions, by virtue of internal preferences and irrespective of external selection.

The specific studies and numbers that are quoted in the chapter mainly focus on male advantages in abstract theoretical reasoning, in particular traditional theoretical mathematics. The general picture presented is of a male preference to systematize, where the female preference is to sympathize. These stereotypes are not new; it was the popularization of peer-reviewed study of them that was new.

Chapter Seven: Hearts and minds

This chapter considers the differences in erotic preferences and behavior between men and women. It starts by introducing difference in expressed preferences for certain physical features, but then turns to psychological and relational aspects. After some caveats regarding the subjectivity of previous work on sexual anthropology, treatment of scientific studies of hormonal influences on libido is introduced. The chapter includes treatment of well-known generalizations like: men being more sexually driven than women, arousal being visual for men and by touch for women, and men wanting sex where women want a relationship. Hormonal explanations for these tendencies are offered, and reference to studies where available. There is a sustained conversational style of presentation in this chapter, which continually returns to the practical difficulties of misunderstandings arising in male-female relationships due to different expectations, especially if the differences between the sexes are denied.

Chapter Eight: Like minds

Treatment of like-mindedness in couples is actually the consistent theme of chapter seven. In this chapter, it is homosexual couples that are on view, in particular male homosexuals—in other words sexual partners with similarly structured brains. Male homosexuals are particularly on view because it would appear that homosexuality in men and women is motivated and expressed quite differently. It would also appear that male homosexuality has been considerably more studied than female homosexuality. The chapter features the work of an East German scientist, Gunter Dörner, from the cold war era. It concludes with a quote from Sigmund Freud: "Bear in mind that some day all our provisional formulations in psychology will have to be based on an organic foundation...It will then probably be seen that it is special chemical substances and processes which achieve the effects of sexuality."

Chapter Nine: The marriage of two minds

This chapter addresses the issue of marital conflict, which it believes to be inevitable, but not fatal. Men and women typically express different goals in life generally, and in personal relationship in particular. The main concern of the chapter is that by educating boys and girls in the same things, and in teaching them that they are the same, society is undermining their future marriages. Essentially the chapter deconstructs modern assumptions regarding equality and power in interpersonal relationships. This is treated mainly from the perspective of women's frustrations within marriages—"the inequality of the emotional contract." It is seen as an inevitability, only made more painful by denial. The chapter concludes by summarizing its warning, while reasserting the complementary diversity it sees as a constructive feature of sexual differences, if embraced. "Marriages go wrong when men and women fail to acknowledge, or begin to resent, each other's complementary differences."

Chapter Ten: Why mothers are not fathers

There are two main themes to this chapter: the complexity and demanding nature of parenting, and the advantages the typical female brain seems to have in applying itself to the challenges. The chapter is explicit in addressing motherhood and fatherhood, not gender-neutral "parenthood." It also addresses both a widespread desire among women to be mothers, and the common experience of guilt among women regarding time spent away from their children. The evolution of social structures in the Israeli kibbutz is reported, where despite an ideological commitment to community, rather than family, investment in raising children, it is the women who have sought and regained the role of motherhood. There is only limited treatment of the role of fatherhood in this chapter.

Chapter Eleven: Minds at work

The main point of chapter eleven is that men and women appear to perceive success differently, they articulate different ambitions. A comparison between the priorities of male and female academics is given. The men, in general, seek publication and status, where the women seek to provide quality education for their students. Several examples of studies along these lines are presented in the body of the chapter. Both publication and personal coaching of students are important contributions to the vitality of educational institutions within the field of academia. The chapter concludes by suggesting that in many fields, the distinctive contributions of typical men and women are actually complementary. Combining the different patterns of talent, rather than denying their existence, is suggested to be a more logical approach to increased productivity in the workplace.

Chapter Twelve: Bias at work

The final chapter of the book argues first that the typical female preference and aptitude for "personal relationships" suits them to employment in workplace roles that capitalize on this. It continues this line of thinking in a creative way, suggesting we have a genuine social problem regarding stereotyping in the workplace; but this problem is not the problem of stereotyping the sexes, rather it is the problem of stereotyping the roles. Management and decision making stereotypes are discussed, and it is suggested that particular "macho" stereotypes predominate. If we want female managers, we should be allowing them to manage in feminine ways, and we might just find these to be workable, and even superior in certain contexts.

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