Biologically deterministic theories about sex, gender, and sexual orientation typically see all three as intrinsically linked and mapping neatly onto each other, with common biological origins. Thus, from this perspective, being female implies being feminine and attracted to males. This assumption forms the basis of what Adrienne Rich terms “compulsory heterosexuality,” the view that heterosexuality and attraction to the opposite sex is natural to the female sex and that any deviation from this is therefore unnatural and open to a wide range of hostile responses on the part of heteronormative societies (1980). Transgender people who reject the sex to which they were assigned at birth are an example of the uncoupling of biological sex and gender identity (Chrisler and McCreary 2010). Although it is the case that for centuries, sex, gender, and sexuality have been seen as different facets of the unified biological essence of men and women, increasingly these three elements are seen as separable and as potentially fluid (Diamond 2009), as discussed in a later section of this chapter.
Biological Theories about Sex and Gender
For some decades the majority of natural and social scientists have come to view extreme biological determinism as an untenable position because of the incontrovertible evidence that human behavior is strongly influenced by social and cultural factors. Thus very few of them would identify as hardline biological determinists and what becomes a matter of dispute is the extent to which scientists emphasize the social or the biological. However recent developments in neuroscience, evolutionary psychology and the “new genetics” have bolstered biologically based explanations of male–female differences (e.g. Buss 1995; Baron‐Cohen 2004; Brizendine 2007), provoking a second wave of feminist critiques of what they see as sexist and deterministic theories and assertions.
As discussed earlier, the aspect of biology seen as central to male–female difference or women's character has shifted over the centuries. Scientists no longer hold that important consequences arise because female bodies are moist whereas those of males are dry, as Galen asserted, or that female moodiness is because the womb has come adrift and is causing havoc, as Plato suggested. There is a number of theories that are actively discussed in recent and current literature and they focus on genes and evolution, hormones, and brains. The links between genes, evolution, hormones, and brains are strong. For example, biological differences between the sexes in brain function are seen by writers such as Herbert (2015) as due to sex‐linked hormones activated in utero and in the first months of life that shape the brain of males and females in different ways. In the following sections some recent theories will be elaborated, along with critical reactions to them.
Evolution and Genes
Sociobiological explanations of sex differences were particularly popular in the 1970s and 1980s with the publication of books like “Sociobiology: The New Synthesis” by Wilson in 1975 and “The Selfish Gene” by Dawkins in 1976. Wilson defined sociobiology as “the systematic study of the biological basis of all social behavior” (1975, p. 4) and argues that human nature is largely dictated by a set of evolved traits. He and other sociobiologists such as Barash (1977) see sexual difference as rooted in our early evolution, at a time, they argue, when the fundamental structure and function of our brains were set down. Given the demands of the primitive life, brains of males and females diverged to suit males to hunting and competitive behavior and women to child‐rearing and nurturing behavior. Such behavioral dimorphism was adaptively advantageous and secured the survival and reproductive success of the species. Barash recommends acquiescing to our biological natures, saying, “there should be a sweetness in life when it accords with the adaptive wisdom of evolution” (1977, p. 25).To sociobiologists, much of both male and female behavior is seen to be explicable in terms of reproductive strategies designed to optimize both sexes' chances of having many healthy offspring, and perpetuating their genes. A small number of theorists claimed to be feminist and advocates of biological determinism. Sayers records the views of “feminist sociobiologists” like Rossi (1977) who consider that,
It is the task of feminism to enable women to get back in touch with their biologically given essence by, among other things, persuading society to construe and value femininity and female biology equally with masculinity and male biology.
(Sayers 1982, p. 147)
Evolutionary theories about human behavior are still strong although the term sociobiology has largely fallen out of use and has been replaced by a number of offshoots such as evolutionary anthropology and evolutionary psychology. Although it is hard to find any proof for hypotheses about sex differences having their origins in cave life, the idea that our basic human propensities are laid down in our genes is still current, typified in this century by the popularity of the work of psychologists like Pinker (2002) and philosophers like Dennett (2003). Commitment to evolutionary and genetic determinism is still strong though challenged by the rise of areas such as epigenetics which examine the ways in which the environment can alter the expression of genes, once thought to be entirely impervious to external influences.
Hormones
Hormones have been a longstanding preoccupation of sex difference theorists. As with other strands of biological determinism, hormones have been resurrected in the twenty‐first century and are now a focus for contemporary brain scientists. Since the discovery of hormones and the fact that hormones act differently in males and females, hormones have been seen as an explanation for observed sex differences and indeed for the particular nature and psychology of women. Fausto‐Sterling was one of the first scientists to offer a resounding critique of theories purporting to show how women were in the grip of their hormones in her book Myths of Gender: Biological Theories about Women and Men, which was first published in 1985 and revised in 1992. She notes that,
some modern psychologists and biologists suggest that women perform more poorly than do men on mathematics test because hormonal sex differences alter male and female brain structures; and many people believe women to be unfit for certain professions because they menstruate. (1992[1985], p. 93)
Fausto‐Sterling examines the literature on the effects of menstruation and menopause on female behavior and finds evidence for significant negative effects resoundingly lacking. She comments on “the morass of poorly done studies on menstruation and menopause” (1992[1985], p. 121) but is heartened by the new research that rejects a traditional misogynistic medical model perspective, which positions women's hormones as toxic and abnormal, and instead situates the experience of menstruation and the menopause in their social contexts (e.g. Beyene 1992). Fausto‐Sterling also examines the evidence for sex differences in aggression. She points out that there is “no clear cut evidence to show that different testosterone levels in adult men and women result in differences in aggression” (1992[1985], p. 141). In fact there is very little evidence for a relationship between circulating hormones such as estrogen and testosterone and any human behavior. Given this reality, researchers often resort to arguments based on the action of fetal androgens on the brain, since the fact that fetal androgens are involved in the establishment of biological sex is incontrovertible. Some neuroscientists and endrocrinologists argue that sex hormones continue to act on the brain throughout life (McEwen and Milner 2017). However, the evidence that fetal hormones shape the human brain for life in a sex‐differentiated manner or that circulating sex hormones have a direct impact on the behavior of adult males and females is weak (Fine 2017).
Brains
Differences in male and female brains have been the focus of attention since the absolute difference in brain size was noted. At first the preoccupation was with the fact that female brains are smaller and therefore, it seemed safe to conclude, less competent (Tuana 1993). But the autopsies of the brains of famous men revealed that they might well have had a brain smaller than that of the average women and it also became clear that there was no correlation between intelligence and the size of the brain (Russett 1989). In general the focus moved