Introduction
You likely accept that men and women possess innate psychological blueprints driven by biology. This view assumes that ancient evolutionary pressures forge divergent paths for male and female behavior, risk tolerance, and social status.
Biological sex does not dictate a rigid template for human behavior, social roles, or economic inequality.
Cordelia Fine names this outdated master narrative Testosterone Rex. The book dismantles this myth across evolutionary biology, neuroscience, endocrinology, and social science. You will discover how flawed assumptions shape modern beliefs about gender.
- Are male and female brains fundamentally different?
- Does testosterone dictate competitive behavior and financial risk?
- Can evolutionary science justify modern social hierarchies?
1. Evolutionary Biology and Sexual Selection
Classic evolutionary paradigms claiming universal male promiscuity and female coyness rely on flawed methodologies and ignore widespread animal kingdom diversity.
Biological sex does not fix a rigid template for mating behaviors across species.
The Bateman Paradigm
The classic experiments that purportedly proved greater male variance in reproductive success and male promiscuity suffered from methodological biases and selectively reported data. In 1948, Bateman used distinct mutant strains of Drosophila melanogaster such as Bristle, Hairless, Hairy-wing, and microcephalous to track parentage in glass containers over three to four days. Modern re-examinations by biologists Brian Snyder and Patricia Gowaty revealed that Bateman's fruit fly data were biased toward counting offspring of males. Data from his first four series showed female reproductive success also increasing with multiple mates, a fact omitted from his later discussion and ignored by subsequent literature. In Bateman's study, 21 percent of males failed to produce any offspring compared to 4 percent of females. Gowaty and colleagues attempted to replicate Bateman's study in 2012 using Drosophila melanogaster and found no evidence of sexual selection.
Animal Kingdom Diversity
DNA paternity testing has disproven the traditional assumption of universal female monogamy across the animal kingdom, revealing rampant female promiscuity. Advances in molecular biology and DNA testing have exposed that females across many species actively mate with multiple partners, a behavior previously obscured by social arrangements like leks or harem-leader structures. In a study of the buff-breasted sandpiper, field observations suggested one male dominated matings. Visual observation attributed 80 percent of matings in the first year and 100 percent in the second year to a single male sandpiper. However, DNA testing of 160 offspring hatched during the sandpiper study showed that 59 different fathers fertilized eggs and 40 percent of broods had multiple fathers. A behavioral ecology journal lists 39 species where female promiscuity brings greater reproductive success.
Female Competition
Female competition for material and social resources heavily influences reproductive success, challenging the view that all females reproduce equally. Because gestating and raising offspring requires substantial energy, access to resources, rank, and territory directly impacts female reproductive success, leading to fierce competition among females in many species. Sarah Blaffer Hrdy spent 10 years studying langur monkeys intermittently in India, observing gray, black-faced langur monkeys where females actively solicited males outside their harem groups. Low-ranking primate females face stress, ovulation suppression, or infanticide from dominant females. Mating carries significant biological and metabolic costs for males, leading to male choosiness and self-imposed chastity in many species. Human males produce 200 million sperm at a time. Mark Elgar's lab observed male stick insects turning down weekly mating opportunities 60 to 70 percent of the time, taking up offered mating opportunities 30 to 40 percent of the time. Meanwhile, male St. Andrew's Cross spiders break their copulatory apparatus during their single mating and are eaten by the female. Bush crickets switch from competitive females to choosy females depending on pollen abundance, and two-spotted goby fish see females take over as the courting sex late in the season as males die off.
2. Human Reproduction and Mating Preferences
Human sexual desires and mate choices are driven by social bonding, economic equity, and emotional intimacy rather than brute reproductive maximization.
Human Reproduction Realities
The theoretical premise that a man can father a hundred babies a year through indiscriminate casual sex is a biological and logistical impossibility in human evolutionary history. Dorothy Einon calculated that a man aiming for one hundred children per year from one-night stands faces a probability of success roughly equivalent to being killed by a meteorite. Healthy couples face a 3 percent probability of pregnancy from a single randomly timed act of intercourse. Feodor Vassilyev's first wife yielded 69 children from 37 pregnancies, while 15 children is the estimated maximum in optimal breeding conditions for a woman.
Representative national surveys reveal that the vast majority of human males and females ideally prefer monogamous, sexually exclusive relationships. The second British National Survey of Sexual Attitudes and Lifestyles surveyed over 12,000 people aged 16 to 44 to reveal a median lifetime total of six partners for men and four for women. Within this NATSAL sample, 80 percent of men and 89 percent of women ideally preferred to be in a sexually exclusive relationship. Famous campus experiments showing stark gender differences in acceptance of casual sex proposals conflate innate sexual nature with profound social and safety risks for women. Russell Clark and Elaine Hatfield stationed male and female decoys on a college campus to proposition strangers with requests for a date, a visit to an apartment, or casual sex. While 50 percent of both men and women agreed to a date with a campus decoy, 69 percent of men agreed to visit a woman's apartment and even more agreed to sex, while zero women consented to sex with a male stranger. Terri Conley proved that this gap disappears when danger, social reputation, the sexual double standard, and expected sexual pleasure are accounted for, especially given the 11 percent chance of female college students experiencing an orgasm from a first casual hookup.
Motivations and Mate Selection
Human sexuality goes far beyond mere reproduction and is fundamentally structured around social bonding and relationships. Greg Laden notes that humans are the only apes lacking a baculum or penis bone, which reduces the efficiency of erection and orgasm in favor of complex psycho-sexual-social bonding. A student survey yielded 237 distinguishable reasons for having sex, including humorous motivations like wanting to change the topic of conversation. Teela Sanders conducted interviews with regular clients of sex workers, such as a 31-year-old man, showing that commercial transactions often attempt to mirror traditional romance and courtship rituals.
People tend to seek partners similar to themselves in attributes like wealth, status, and appearance rather than trading youthful fertility for resources. Peter Buston and Stephen Emlen surveyed close to a thousand U.S. college students to pit potentials-attract against likes-attract preferences. The results showed that the likes-attract hypothesis performed much better in explaining people's actual mate preferences. Wendy Wood and Alice Eagly noted shifts in mate preferences between 1939 and 2008 as traditional male breadwinner roles broke down, demonstrating that mate preferences shift alongside changing social roles.
3. Brain Mosaics and Behavioral Similarities
Biological Foundations of Sex
Biological sex determination is far more complex than a simple binary driven by the Y chromosome, involving dozens of genes and resulting in intersex variations. 98 to 99 percent of the population have XY chromosomes and male genitals or XX chromosomes and female genitals.
While the traditional view holds that the SRY gene on the Y chromosome acts as a binary switch determining male or female development, modern science shows that sex determination is a complex process involving genes scattered across multiple chromosomes. About one to two percent of the population are intersex, where genes, gonads, and genitals do not neatly align into the male or female binary.
Individuals with an XY chromosome pair whose receptors do not respond to androgens develop male testes but female external genitalia.
Brain Mosaics and Similarities
Human brains and psychological traits do not fall into dimorphic male and female categories, but consist of unique mosaics with vast behavioral overlap.
Daphna Joel and researchers analyzed large human brain datasets and found that having consistently all-male or all-female brain characteristics is extremely rare. Instead, the vast majority of individuals possess a mix of features that fall on both the male-end and female-end of various continuums.
Researchers analyzed brain images from more than 1,400 human brains across four different data sets and found that only 0 to 8 percent of people had exclusively female-end or male-end features. 23 to 53 percent of individuals had brains with both male-end and female-end features.
Janet Hyde's synthesis of multiple meta-analyses demonstrated that over three-quarters of psychological sex differences are small or very small, meaning there is enormous behavioral overlap between men and women. Janet Hyde synthesized forty-six meta-analyses, later followed by a ten-year update covering 106 meta-analyses, confirming that most cognitive and personality traits show minimal divergence between sexes.
4. Risk, Competitiveness, and Social Norms
Apparent gender differences in risk-taking and competitiveness stem from subjective risk perceptions, cultural contexts, and social backlash rather than innate biology.
Risk Perception and Attitudes
Risk-taking is not a stable personality trait across your life. A person willing to take risks in business may avoid them in health or finance. Elke Weber and colleagues surveyed undergraduates across six domains such as gambling, financial, health, recreational, social, and ethical decisions, finding no consistent risk pattern.
Apparent risk-takers do not love danger per se. They perceive greater benefits and lower personal costs. Wire-walker Philippe Petit, famous for walking between the Twin Towers, explicitly described himself as the exact opposite of a daredevil.
Men and women exhibit very similar risk attitudes when evaluating the same subjectively perceived risks and benefits. Studies of eighteen- to twenty-one-year-olds found males reported more drinking and drug-taking, but for older adults, this sex difference reversed.
Traditional questionnaires on risk-taking suffer from implicitly gendered assumptions. They ignore hazards commonly faced by women, such as pregnancy, career interruptions for childcare, dating, or wearing high heels. Being pregnant in the United States is about twenty times more likely to result in death than a skydive.
Differences in risk perception often stem from social privilege rather than sex biology. James Flynn and colleagues surveyed over 1,500 U.S. households and found that white hierarchical and individualistic males stood out from all other groups in their cavalier attitude toward risks.
Gender norms and the threat of social backlash heavily dictate whether you choose to take certain risks or negotiate. Michelle Ryan surveyed over 800 managers and found women were less willing to take career risks because they perceived fewer benefits due to lower support, fewer role models, and less organizational meritocracy.
Cultural Variation in Competitiveness
Inherent male competitiveness is contradicted by cross-cultural studies. Women are just as competitive when contexts match their social environments. Men from the patriarchal Maasai society in Tanzania were more willing to compete to earn money by throwing balls into a bucket, whereas the exact opposite was observed in the matrilineal Khasi society in India.
Attributing workplace inequality to innate female risk-aversion or lack of competitiveness unfairly blames women. It obscures systemic harassment and discrimination. A survey of over 3,500 Australian surgeons revealed a culture rife with bullying, discrimination, sexual harassment, and a culture of fear.
5. Hormones, Context, and Behavior
Testosterone is frequently blamed as the biological culprit behind workplace and social inequalities between sexes, acting as a supposed master hormone of masculinity. Scholars like law professor Kingsley Browne and neuroscientist Joe Herbert have argued that testosterone is the biological wellspring of masculinity and workplace gaps.
Testosterone is not an omnipotent master hormone that unilaterally dictates human behavior and social inequalities.
Behavioral endocrinologist Richard Francis coined the term Testosterone Rex to mock this mistaken view of the hormone as an omnipotent plenipotent executor. Scientific views often position testosterone as a super-actor that takes care of everything from physique to dominance and risk-taking. Circulating blood testosterone is only a crude indicator of hormonal influence because the brain-hormone system involves numerous complex variables and receptors.
Testosterone interacts with a multilayered system involving cofactors, androgen and estrogen receptors, localized sensitivity, and enzymes like aromatase that convert testosterone into estrogen within the brain itself. Absolute testosterone levels in blood or saliva provide only a very rough guide to actual neural effects.
The Testosterone Rex Myth
Hormones do not act as kings that issue direct behavioral commands. They alter response thresholds and make specific behaviors more likely depending on context.
In studies of talapoin monkeys, high doses of testosterone given to castrated males only increased aggression toward lower-ranking males. Relative social status filtered any hormonal effect and no animal rose in rank.
Dynamic Hormones and Social Regulation
Social events and status regulate gonadal events rather than high testosterone levels unilaterally creating dominant behavior. In studies of Haplochromis burtoni cichlid fish by Rui Oliveira and colleagues, social success and territory establishment caused successful fish to produce more androgens, not vice versa.
Social actions and contexts can dynamically influence testosterone levels just as much as hormones influence actions. Lee Gettler's longitudinal study of fathers in the Philippines showed that fatherhood reduced testosterone levels in men, and the decrease was greater for fathers who spent more time physically caring for their infants.
Human cultural practices and gendered expectations actively shape and modulate testosterone reactivity. In a study by Sari van Anders, female actors who enacted workplace power by firing an employee experienced a significant increase in testosterone, indicating that gendered behavior and power displays modulate hormone levels.
Justin Carré and colleagues found that men who participated in the ten-year Fast Track intervention program designed to build social competencies showed less testosterone reactivity to provocation and were less likely to retaliate compared to a control group. According to the biosocial model published in 1985 by Mazur and Booth, as well as comparative work by researchers like S. Marc Breedlove and S. M. van Anders, social victories increase testosterone while defeats or fatherhood can decrease it.
6. Financial Risk and the Lehman Sisters Myth
Claims that female leadership or lower testosterone prevents financial crises rely on publication bias, flawed risk tasks, and harmful stereotypes.
Commentators and researchers frequently invoke evolutionary explanations and testosterone levels to argue that a greater diversity of hormones would bring financial conservatism. Following the financial crisis, media outlets and magazines like Time highlighted female financial regulators like Elizabeth Warren, Sheila Bair, and Mary Schapiro as being charged with cleaning up the mess made by men.
Financial Risk and Methodology
Economist Julie Nelson reviewed eighteen studies and found that researchers tend to summarize earlier results inaccurately, emphasize stereotype-consistent findings, and downplay null results or counter-findings. Funnel plots demonstrate that smaller studies disproving male risk-taking are systematically omitted from publication.
Studies comparing diverse human populations, such as small-scale farmers in Chile and Tanzania or general populations in China, frequently find no sex differences in financial risk-taking. Researchers Joseph Henrich and Richard McElreath used traditional lottery tasks with Mapuche farmers in Chile and Sangu farmers in Tanzania and found that sex was not linked with risk-taking propensity. A study with four hundred Chinese participants sampled also found no sex difference.
When abstract lotteries are translated into concrete domains like pensions or salaries, or when stakes are raised from trivial amounts to substantial sums, sex differences in risk preferences often vanish. Researchers Ivo Vlaev and colleagues found no sex differences when lotteries were presented in real-world contexts such as mortgages, salaries, and insurance rather than abstract terms, using a thirty pound daily payment versus a fifty percent chance of one hundred pounds.
Identity and Hormones on the Trading Floor
When mathematical or financial tasks are framed using masculine stereotypes or when participants must record their gender beforehand, women often exhibit increased risk aversion due to stereotype threat. Vishal Gupta and colleagues showed that Turkish MBA students evaluated business opportunities differently depending on whether entrepreneurs were described in stereotypically masculine terms versus gender-neutral or feminine terms.
Marc-André Reinhard and colleagues found that giving men failure-as-an-asset feedback increased their self-reported interest in risky activities and the amount they were prepared to invest in a gamble. Although digit ratio is frequently used as a putative marker of prenatal testosterone, it is far too noisy an index for individuals within a group. John Coates and Joe Herbert linked higher circulating testosterone levels in male traders to higher profits, but noted that testosterone can become detrimental by making traders overly aggressive in bull markets.
Michelle Ryan coined the glass cliff effect to describe the well-documented bias where women are placed in leadership roles during times of crisis. Speculations that women possess inherent financial conservatism come with dangerous implications, pigeonholing women into cleaning up messes while men manage growth. Increasing senior female representation is crucial because it indicates the breakdown of harmful gender stereotypes and discourages toxic locker-room behavior.
7. Toys, Marketing, and Developmental Systems
Rigid gender socialization through marketing and essentialist beliefs reinforce inequality by ignoring the dynamic nature of human developmental systems.
Gendered Toy Marketing
Sex-segmented toy marketing and color-coding rely on the false assumption of innate biological preferences. Marketers argue that products reflect evolutionary differences between boys and girls.
Psychologists Wang Wong and Melissa Hines compared children's play times with a train and a doll. Sex differences shrank when the toys appeared in counterstereotypical colors like a pink train and a blue doll.
Campaigns such as Pink Stinks and Let Toys Be Toys operate in the United Kingdom to eliminate gendered toy segregation. A 2012 study by Auster and Mansbach on toy marketing on the Disney store website highlights how pointlessly gendered products shape development.
Essentialism and Social Change
Essentialist thinking groups adaptiveness, fixity, and typicality together. Paul Griffiths explains that people assume evolutionary adaptations are unchangeable and universal.
Selective breeding experiments with mice demonstrate the flexibility of traits. After seven generations of selective breeding in the mouse aggression experiment, and up to thirty-nine generations, rearing thuggish mice in social groups completely eliminated their aggressive behavior.
You can dismantle inequality by rearranging the developmental system rather than accepting biological determinism. Wendy Wood and Alice Eagly point out that postindustrial technological changes have facilitated a rapid merging of sex roles.
- Challenge gender essentialist views that frame inequality as natural.
- Eliminate pointlessly gendered products for children.
- Restructure external developmental systems and social norms.
10 Key Ideas
- Biological sex does not dictate a rigid template for human behavior, social roles, or economic inequality across species or human societies.
- Human sexual desires and mate choices are driven by social bonding, economic equity, and emotional intimacy rather than brute reproductive maximization.
- Human brains and psychological traits do not fall into dimorphic male and female categories, but consist of unique mosaics with vast behavioral overlap.
- Apparent gender differences in risk-taking and competitiveness stem from subjective risk perceptions, cultural contexts, and social backlash rather than innate biology.
- Testosterone is not an omnipotent master hormone that unilaterally dictates human behavior and social inequalities, but interacts with a multilayered system influenced by social context.
- Claims that female leadership or lower testosterone prevents financial crises rely on publication bias, flawed risk tasks, and harmful stereotypes.
- Rigid gender socialization through marketing and essentialist beliefs reinforce inequality by ignoring the dynamic nature of human developmental systems.
- Animal kingdom diversity and DNA paternity testing disprove traditional assumptions of universal female monogamy and male coyness.
- Cross-cultural studies demonstrate that female and male competitiveness shifts dynamically depending on social environments and cultural norms.
- Essentialist thinking erroneously groups adaptiveness, fixity, and typicality together, ignoring how rearranging developmental systems and social norms can dismantle inequality.