The Red Queen: Sex and the Evolution of Human Nature

Science writer Matt Ridley, drawing on evolutionary biology, genetics, and anthropology, argues that sexual reproduction is the central force shaping human nature. His central thesis is that a universal human nature exists, that it was shaped by natural selection, and that understanding it requires understanding how human sexuality evolved. The book's title refers to the Red Queen from Lewis Carroll's Through the Looking-Glass, a chess piece who must run constantly just to stay in the same place. In biology, the Red Queen concept captures the idea that organisms must keep evolving to maintain their relative position, because their competitors and parasites are evolving too.

Ridley begins by establishing that human nature is both universal and shaped by evolution. He contends that reproduction is the sole goal for which human beings were designed by natural selection, and that all other traits are means to that end. He frames the nature-nurture debate as a false opposition: Culture itself is a product of evolved human tendencies. He cites biologist August Weismann's insight that the germ-plasm (sex cells) is kept separate from the body, meaning acquired traits cannot be inherited, and evolutionary biologist Richard Dawkins's gene-centered view that bodies are vehicles for genes.

The book's first major puzzle is why sex exists at all. Asexual reproduction is theoretically twice as efficient, since an asexual female passes all her genes to every offspring. This "cost of males," as biologist John Maynard Smith termed it, means any asexual mutant should outcompete sexual rivals. Ridley reviews several explanations. The "Vicar of Bray" hypothesis, associated with Weismann and evolutionary theorists Ronald Fisher and Hermann Muller, held that sex speeds evolution by combining beneficial mutations, but this relies on group-selectionist logic. Evolutionary biologist George Williams's 1966 book Adaptation and Natural Selection exposed these flaws and demanded that sex be explained as beneficial to individuals. Molecular biologist Harris Bernstein's DNA repair theory and theorist Alexey Kondrashov's mutation-purging model receive attention but are found insufficient.

Ridley finds the most compelling answer in parasites. The Red Queen hypothesis holds that organisms must keep reshuffling their genes through recombination, the process by which genes are rearranged during sexual reproduction, to stay ahead of parasites constantly evolving new attacks. He uses the metaphor of locks and keys: Parasites evolve protein "keys" to break into host cells, and hosts must change their genetic "locks." Evolutionary biologist Bill Hamilton built computer models showing that sexual reproduction can overcome its twofold disadvantage by generating new combinations of resistance genes. Biologist Curtis Lively's studies of New Zealand water snails provided empirical support: Sexual populations resist parasites better than clonal (asexually produced, genetically identical) populations. Ridley addresses the counterexample of bdelloid rotifers, tiny freshwater animals that have reproduced without sex for tens of millions of years, noting that their ability to desiccate into dormant "tuns" may serve as an alternative anti-parasite strategy.

Having explained why sex exists, Ridley turns to why there are exactly two genders. He traces their origin to conflicts among organelles (mitochondria and chloroplasts) when cells fuse during sexual reproduction. Nuclear genes resolved this conflict by mandating that one parent's organelles be destroyed, creating two roles: one that contributes organelles (female) and one that does not (male). Sperm evolved to be stripped of cytoplasm, the cell material surrounding organelles, as a biological safeguard. Ridley introduces the hypothesis of evolutionary theorist Robert Trivers and his collaborator Dan Willard: In polygamous species, parents in good condition should produce more sons (the high-risk, high-reward sex), while those in poor condition should favor daughters. Researcher Valerie Grant's study suggests that dominant human women are more likely to have sons.

Sexual selection occupies a pivotal section. Ridley explains Trivers's parental investment theory: The sex investing more in offspring (typically female) is choosier about mates, while the sex that invests less competes for access. He describes the debate between two camps. The Fisherian camp argues that female preferences are arbitrary fashions that become self-reinforcing. The Good-genes camp argues that ornaments honestly signal genetic quality. Theorist Amotz Zahavi's handicap principle holds that costly ornaments are honest signals precisely because only fit males can afford them. Hamilton and zoologist Marlene Zuk proposed that parasites solve the "lek paradox," the puzzle of why genetic variation persists despite generations of selective mating: Because parasites constantly evolve new attacks, the genes defining the "best" males change every generation.

Ridley applies these principles to human mating. He argues that men are naturally inclined toward opportunistic polygamy, citing anthropologist Laura Betzig's cross-cultural analysis showing that rulers in all six independently arising early civilizations translated power into enormous harems, employing claustration (the seclusion and confinement) of concubines to maximize reproductive output. Anthropologist Napoleon Chagnon's data on the Yanomamö of Venezuela showed that men who had killed other men had more wives regardless of social standing. Ridley traces the historical arc from despotic polygamy through the invention of agriculture to modern democracy, which largely restored monogamy.

Turning to female strategy, Ridley argues that women pursue what he calls the "Emma Bovary strategy": securing a reliable provider while sometimes pursuing genetically superior partners. Researchers Robin Baker and Mark Bellis found that women's orgasm patterns may unconsciously favor conception with lovers over husbands. Ridley argues that concealed ovulation, unlike the visually obvious fertile periods of chimpanzees, helps women manage this dual strategy. Researchers Margo Wilson and Martin Daly showed that across cultures, male sexual jealousy is the leading provocation for spousal homicide.

Ridley devotes attention to psychological sex differences. He identifies four consistently replicated differences: Girls excel at verbal tasks, boys at mathematical tasks, boys show more aggression, and the sexes differ in visuospatial abilities (men excel at mental rotation; women at object-location memory). He traces these to the Pleistocene, the prehistoric era when humans lived as hunter-gatherers, arguing that hunting favored male spatial navigation while gathering favored female object-location memory. Cross-cultural researcher David Buss's study of mate preferences across 33 countries finds that men prioritize youth and attractiveness while women prioritize wealth and status, and that high-earning women value earning capacity in mates even more than low-earning women do.

On beauty, Ridley argues that standards of attractiveness are neither wholly cultural nor arbitrary. Researcher Dev Singh's work on waist-to-hip ratio shows that men consistently prefer the lowest ratio regardless of overall body weight. Scientist Francis Galton's 1883 discovery that composite faces are judged more attractive than individual ones suggests that beauty involves proximity to a population average rather than extreme features.

The book's final major argument is that human intelligence may be a product of social and sexual competition rather than ecological challenges. Ridley presents the Machiavellian intelligence hypothesis, independently proposed by biologist Richard Alexander and psychologist Nicholas Humphrey: The primary selective pressure driving brain growth was competition with other humans, not with the physical environment, because social challenges escalate indefinitely as competitors also become smarter. Cognitive scientist Leda Cosmides's experiments show that people excel at detecting cheaters in social contracts but fail at identical abstract logic problems, suggesting the mind contains specialized social-reasoning modules. Evolutionary psychologist Geoffrey Miller proposes that intelligence is a sexually selected trait, driven by mutual mate choice for wit and creativity. Ridley adds that neoteny, the retention of juvenile features into adulthood, may have created a self-reinforcing cycle: Preference for younger-looking mates spread genes that slowed developmental aging, producing adults with larger brains capable of more sophisticated mate choice.

Ridley concludes by characterizing humans as self-domesticated apes whose evolved nature persists beneath civilization. He acknowledges that many of the book's ideas may prove wrong but maintains that the evolutionary perspective, centered on the Red Queen's endless race, represents genuine progress toward understanding human nature.