…the world must be peopled. — Benedick

adaptation  affairs  altruism altruism (reciprocal) chastity  beauty commitment conflict between the sexes Coolidge effect  courtship  coyness  cuckoldry  evolutionary psychology  evolutionary success story  fidelity  fitness  fitness indicator  fitness matching  genes inclusive fitness infidelity jealousy mate choice mate preferences mateship natural selection paternity uncertainty proprietariness reproduction reproductive value sperm-competition strategic interference tree of life  virginity youth


Adaptations are evolved solutions to the problems posed by survival and reproduction. (Buss 2003:5)

Adaptations may be defined as evolved solutions to specific problems that contribute either directly or indirectly to successful reproduction. (Buss 2008:15–16)

Hypotheses about adaptations are, in essence, probability statements about why a reliable, efficient, and economic set of design features could not have arisen by chance alone… (Buss 2008:16)

The human eye, for example, is constructed by hundreds of genes. The fact that genes are required for adaptations, however, does not mean that human behavior is “genetically determined”… Past environments selected the genes we have today; environments during a person’s lifetime are necessary for the proper development of adaptations, and current environments are responsible for activating adaptations once they have developed. … The reliably developing feature of adaptations does not mean that the adaptation must appear at birth. (Buss 2008:39)

And so the core of all animal natures, including humans, consists of a large collection of adaptations. Some of these adaptations are sense organs… Some of these adaptations help us to move through our environment… Evolutionary psychologists tend to focus on one special subclass of the adaptations that comprise human nature—psychological adaptations and the by-products of those adaptations. (Buss 2008:42)

The device designed by Darwin to counteract Paley’s argument from design was adaptation. This concept is at the center of the evolutionary representation of the world. (Jacob 1982:19)

A biological trait that evolved through natural selection or sexual selection to promote survival or reproduction in a particular way. (Miller 2001:436)


Affairs also provide an opportunity to evaluate potential husbands, supplying additional information that is unavailable through mere dating without sexual intercourse. Given the tremendous reproductive importance of selecting the right husband, women devote great effort to evaluation and assessment. Affairs prior to marriage allow a woman to assess the intentions of the prospective mate… (Buss 2003:87)

Affairs involve willing women. Willing women demand benefits. (Buss 2003:95)


The overall conclusion, if these arguments are right, is that even the most thorough-going form of materialist Darwinism allows us a capacity for genuine altruism. … All versions allow for altruism; none sees it as all-pervasive. (Radcliffe Richards 2008:184)

Altruism (reciprocal)

Reciprocal altruism… is an example of what Wilson calls ‘‘soft-core altruism,’’ actions undertaken with the expectation that society will reciprocate. Our task here, once again, is to try to understand hard-core altruism. (Frank 1988:29)

Tit-for-tat, reciprocal altruism, kin selection, and other conventional evolutionary accounts of unopportunistic behavior paint a very different picture of human nature. Indeed, for all their obvious value, these accounts do not explain genuinely unopportunistic behavior at all. (Frank 1988:69)

The work of evolutionary biologist Robert Trivers on reciprocal altruism has gone a long way toward explaining cooperation among unrelated friends and strangers. Trivers’s model incorporates many of the psychological friends and social factors related to altruism and reciprocity, including: friendship, moralistic aggression (i.e., the punishment of cheaters), guilt sympathy, and gratitude, along with a tendency to deceive others by mimicking these states. (Harris 2010:56)


These circumstances upset some people, because they seem unfair. We can modify our physical attractiveness only in limited ways, and some people are born better looking than others. Beauty is not distributed democratically. A woman cannot alter her age, and a woman’s reproductive value declines more sharply with age than a man’s; evolution deals women a cruel hand, at least in this regard. Women fight the decline through cosmetics, through plastic surgery, through aerobics classes… (Buss 2003:70–71)

But standards of attractiveness are not arbitrary—they reflect cues to youth and health, and hence to reproductive value. Beauty is not merely skin deep. It reflects internal reproductive capabilities. (Buss 2003:71)

…our standards for female beauty should embody cues to women’s reproductive value. Conventional wisdom dictates that beauty is in the eyes of the beholder, but those eyes and the minds behind the eyes have been shaped by millions of years of human evolution. Beauty is in the \textit{adaptations} of the beholder… (Buss 2008:147)

No training seems necessary for these standards to emerge. … Beautiful female faces, in short, are especially rewarding to men, psychologically and neurologically. (Buss 2008:149)

Men’s preference for physically attractive mates appears to be the product of a species-wide psychological mechanism that transcends cultural variation. (Buss 2008:154)


Before the use of modern contraceptives, chastity provided a cue to the future certainty of paternity. On the assumption that a woman’s proclivities toward chaste behavior would be stable over time, her premarital chastity signaled her likely future fidelity. A man who did not obtain a chaste mate risked becoming involved with a woman who would cuckold him. (Buss 2003:67)

In traditional societies, daughters are sold for a bride-price, and since a virgin is guaranteed not to be bearing another man’s child, chastity is a selling point. (Pinker 2011:396)


Commitment, however, has many facets. One major component of commitment is fidelity, exemplified by the act of remaining faithful to a partner when they are separated. Fidelity signals the exclusive commitment of sexual resources to a single partner. Another aspect of commitment is the channeling of resources to the loved one, such as buying her an expensive gift or ring. (Buss 2003:43)

Sincerity in personal advertisements is a code word for commitment, used by women to screen out men seeking casual sex without any commitment. (Buss 2003:44)

Conflict between the sexes

The findings from these studies present a framework for understanding conflict between the sexes as stemming from our evolved mating strategies. (Buss 2003:142)

Conflict exists in a particularly complicated form between men and women because human beings are the most cooperative species on earth; that’s the central claim of this book. (Seabright 2012:6)

Sexual conflict, far from being uniquely human, is everywhere is nature… Females of many species deploy in turn a startling variety of counter-strategies, ranging from body armor to sperm barriers to sisterly coalition building—expensive biological investments that would be mystifying if resistance to sex were merely the product of Victorian inhibition. (Seabright 2012:7)

No human soap opera could outstrip in violence, hypocrisy, and manipulation the daily drama of relations between the sexes across the entire animal kingdom. Why does nature work that way, and what does it mean for us? (Seabright 2012:8)

…sexual relations in almost all species are clouded by the possibility that either partner might be better off with someone else, now or in the future. … To say there’s conflict doesn’t mean that male and female interests are completely opposed—far from it. It means just that they’re not completely aligned. And even a slight difference in priorities can create vast potential for mistrust. (Seabright 2012:9)

The conflicts of interest between men and women arise for two distinct reasons. The first is that when couples bargain together… they’re not completely transparent to each other. The second is that even if they were transparent, they’d be unable to commit completely to doing what they undertake to do… (Seabright 2012:9–10)

Sexual conflict, then, is the shadow cast by cooperation… (Seabright 2012:11)

When playing the Administrator of Evolution, and trying to maximize genetic legacy, you quickly discover that this goal implies different tendencies for men and women. Men can reproduce hundreds of times a year, assuming they can persuade enough women to cooperate… Women, on the other hand, can’t reproduce more often than once a year. (Wright 1995:35)

…there comes a time when having more sex just isn’t worth the trouble [for a woman]. Better to get some rest or grab a bite to eat. For a man, unless he’s really on the brink of collapse or starvation, that time never comes. … And even in the more recent past, after the arrival of language and self-awareness, there has been no reason for every evolved behavioral tendency to fall under conscious control. (Wright 1995:36)

Coolidge effect

The Coolidge effect ostensibly got its name when President Calvin Coolidge and his wife were touring a farm. The foreman noted the sexual prowess of his prize rooster: ‘This rooster can have sex all day without stopping,’ he said. ‘Really?’ said Mrs. Coolidge. ‘Please tell that to my husband.’ The president turned to the foreman and asked, ‘Does the rooster mate with the same chicken each time?’ ‘No,’ said the foreman. To which the president replied, ‘Really? Please tell that to my wife.’ (Gilbert 2007:252–53)


In long-term mating, both men and women prefer a lengthy courtship, in a process that permits evaluation of the nature and magnitude of the assets the person possesses and the costs they carry. (Buss 2003:98)

…many species appear to use their courtship behaviors as fitness indicators. The distinctive thing about humans is that our courtship behavior reveals so much more of our minds. Art reveals our visual aesthetics. Conversation reveals our personality and intelligence. By opening up our brains as advertisements for our fitness, we discovered whole new classes of fitness indicators, like generosity and creativity. (Miller 2001:105)

…because courtship is a way to arouse sexual interest in someone who is not already interested, courtship displays that make explicit reference to sex may be particularly unappealing. (Miller 2001:381–82)

Human courtship, like courtship in other animals, has a typical time-course. Courtship effort is low when first assessing a sexual prospect, increases rapidly if the prospect reciprocates one’s interest, peaks when the prospect is deciding whether to copulate, and declines once a long-term relationship is established. (Miller 2001:383)

The attractive forms of novelty tend to rely on a uniquely human trick: the creative recombination of learned symbolic elements (e.g. words, notes, movements, visual symbols) to produce novel arrangements with new emergent meanings (e.g. stories, melodies, dances, paintings). This trick allows human courtship displays not just to tickle another’s senses, but to create new ideas and emotions right inside their minds, where they will most influence mate choice. Scheherazade did not produce a random series of nonsense words to play upon the sultan’s neophilia. She took existing words that already had a meaning, and put them together in new combinations that evoked new characters, plots, and images. (Miller 2001:413)


For women, sexual withholding fulfills several possible functions. One is to preserve their ability to choose men of high quality who are willing to commit emotionally and invest materially. (Buss 2008:329)

Coyness may not be an inherently female strategy, but it’s sometimes in the interests of females to make their males think it is, especially in response to the sometimes violent jealousy of males. If Victorian moralists were under the impression that women’s sexual appetites were inherently limited, that shows only how effectively the wool had been pulled over their eyes by countless generations of women. (Seabright 2012:19)


In mammals, including Homo sapiens, the female is the sex making the greater parental investment, while males devote proportionately more time and energy to mating competition. Male mammals attempt to monopolize females and their reproductive capacity just as creatures contest any limited resource. But men, unlike most male mammals, make significant parental investments, too, and the combination of this paternal investment with an asymmetrical risk of cuckoldry (misattribution of parenthood) produces a powerful selective force favoring the evolution of motives that effectively guarantee one’s paternity of one’s putative offspring… psychological mechanisms whose adaptive functions are success in sexual competition and cuckoldry avoidance. … men’s attitudes, emotions, and actions indicative of sexual proprietariness and the commoditization of women are the products of these evolved mechanisms… (Wilson and Daly in Barkow et al. 1992:290)

Marital ties are thinner gruel: Because cuckolded males risk expending their lives unwittingly raising their rivals’ children, the correlation between the expected fitnesses of mates can be abolished or reversed by infidelity. … One strategic means for reducing the costs of cuckoldry is adjusting parental efforts according to cues indicating the likelihood of genetic parenthood… (Wilson and Daly in Barkow et al. 1992:291)

…a major threat to a man’s fitness is the possibility that his mate may become pregnant by another man, especially if the cuckold should fail to detect the fact and invest in the child as his own. (Wilson and Daly in Barkow et al. 1992:292)

Consider the reaction in Greek culture to cuckoldry [quoting Safilios-Rothschild]: “The wife’s infidelity… brings disgrace to the husband who is then a Keratas—the worst insult for a Greek man—a shameful epithet with connotations of weakness and inadequacy. … While for the wife it is socially acceptable to tolerate her unfaithful husband, it is not socially acceptable for a man to tolerate his unfaithful wife and if he does so, he is ridiculed as behaving in an unmanly manner.” Cuckolded men are universal objects of derision. (Buss 2003:126)

These legal strictures reflect an intuitive understanding of human evolutionary psychology: cuckoldry represents the unlawful stealing of another man’s resources. Men everywhere seem to regard wives as chattel to be owned an controlled. Men everywhere react to cuckoldry as they would to theft, and sometimes leave a trail of destruction in their wake. (Buss 2003:140)

The human male is unusual among mammals in that he feeds, protects, and cares for their mother. But this investment is genetically risky. If a man’s wife has a secret dalliance, he could be investing in another man’s child, which is a form of evolutionary suicide. Any genes that incline him to be indifferent to cuckoldry will lose out over evolutionary time to genes that incline him to be vigilant. As always, genes don’t pull the strings of behavior directly; they exert their influence by shaping the emotional repertoire of the brain, in this case, the emotion of sexual jealousy. Men are enraged at the thought of their partner’s infidelity, and they take steps to foreclose that possibility. (Pinker 2011:396)

Evolutionary psychology

Evolutionary psychology represents a true interactionist view, which identifies the historical, developmental, cultural, and situational features that formed human psychology and guide that psychology today. (Buss 2003:17)

Evolutionary psychology focuses on four key questions: (1) Why is the mind designed the way it is…? (2) How is the human mind designed…? (3) What are the functions of the component parts and their organized structure…? (4) How does input from the current environment interact with the design of the human mind to produce observed behavior? (Buss 2008:2–3)

The job of evolutionary psychology is to analyze how evolution constructs these mental adaptations that turn environmental cues into fitness-promoting behaviors. The larger the brain, the more sophisticated the environmental cues it can use to guide behavior, and the more sophisticated that behavior. (Miller 2001:393)

One of the fundamental arguments of the new evolutionary psychology is that it is wrong to view the mind as a general-purpose learning mechanism… (Mithen 1996:9–10)

…a key insight of evolutionary psychology is that human cooperation and the social emotions that support it, such as sympathy, trust, gratitude, guilt, and anger, were selected because they allow people to flourish in positive-sum games. (Pinker 2011:76)

Evolutionary success story

Every human alive is an evolutionary success story. If any of our ancestors had failed to survive an ice age, a drought, a predator, or a plague, they would not be our ancestors. If any had failed to cooperate with at least some others in the group or dropped below a minimal position in the social hierarchy, they would have met certain death by being cast out from the group. If even one had failed to succeed in choosing, courting, and keeping a mate, the previously inviolate chain of descent would have irreparably broken, and we would not be alive to tell the tale. Each of us owes our existence to thousands of generations of successful ancestors. As their descendants, we have inherited the passions that led to their success—passions that drive us, often blindly, through a lifelong journey in the struggle for survival, the pursuit of position, and the search for relationships. (Buss 2000:1)


If ancestral couples had always remained faithful, there would have been no selection pressure for the intense concern with fidelity. (Buss 2003:72)


The average number of children is a measure of a genotype’s Darwinian fitness, which is the basic quantity for evaluating the intensity of natural selection. (Bodmer and Cavalli-Sforza 1976:275)

Fitness in this evolutionary sense has three important features: it is relative to competitors in a species, it is relative to an environment, and it is a statistical propensity rather than an achieved outcome. … Genes underlying high fitness will tend to spread through a population, replacing genes for low fitness. Evolution increases fitness, by definition. (Miller 2001:107)

Fitness as a propensity is the most slippery concept to grasp. Fitness as I use the term is a statistical propensity, an expectation that allows us to predict how an individual will probably fare. (Miller 2001:107–8)

(1) The relative reproductive success (including survival ability) of one set of genes relative to others. (2) Good physical or mental condition that might prove genetically heritable. (Miller 2001:439)

Fitness indicator

Our hominid ancestors… had to make do with fitness indicators such as sexual ornaments and courtship displays. By definition, fitness indicators have some correlation with fitness, but is never a perfect correlation. The handicap principle keeps indicators relatively honest, but it cannot keep them perfectly honest, so there will always be a discrepancy between true fitness and apparent fitness. The evolution of fitness indicators is driven by this discrepancy. (Miller 2001:199)

An adaptation that evolved to advertise an individual’s fitness during courtship and mating, typically by growing an ornament or performing a behavior that lower-fitness individual would find too costly to produce. (Miller 2001:439)

Fitness matching

Fitness matching, a form of mutual mate choice based on fitness indicators, may be a more sensible explanation for most sexual ornaments that show very small sex differences. (Miller 2001:203)

The assortative mating for fitness that happens in a competitive mating market when individuals mate with the highest-fitness sexual partner who is willing to mate with them. (Miller 2001:439)


Genes, of course, do not have thoughts, and none of this occurs with consciousness or intentionality. The key point is that the gene is the fundamental unit of inheritance, the unit that is passed on intact in the process of reproduction. Genes producing effects that increase their replicative success will replace other genes, producing evolution over time. Adaptations are selected and evolve because they promote inclusive fitness. (Buss 2008:14)

Inclusive fitness

Inclusive fitness is calculated from an individual’s own reproductive success plus his effects on the reproductive success of his relatives, each one weighed by the appropriate coefficient of relatedness. (Dawkins 1989:186)


Infidelity represents the partial diversion of evolutionarily valuable resources. Desertion, abandonment, and defection from the relationship represent the entire loss of those assets. … The most dramatic threats to the fragile unions between men and women, in short, are the dual specters of infidelity and abandonment. (Buss 2000:35)

When it comes to laws and other sanctions, the Golden Rule applies with a vengeance; those who have the gold make the rule. Throughout human recorded history, most laws have been written and legislated by men, so they reflect a male rather than a female psychology. Across most cultures over human recorded history, an infidelity by the wife is considered to be analogous to a ‘‘property violation’’ against the husband. (Buss 2000:187)

Men abhor promiscuity and infidelity in their wives. Unfaithfulness proves to be more upsetting to men than any other pain a spouse can inflict on her mate. (Buss 2003:69)

Sperm insemination increases when other men’s sperm might be inside the wife’s reproductive tract at the same time, as a consequence of the opportunity provided for extramarital sex by the couple’s separation. This increase in sperm is precisely what would be expected if humans had an ancestral history of some casual sex and marital infidelity. (Buss 2003:75)

A wife’s infidelity is sometimes viewed as so extreme a provocation that a “reasonable man” may legally respond with lethal violence. In Texas until 1974, for example, it was legal for a husband to kill his wife and her lover if he did so while the adulterers were engaging in the act of intercourse; their murder was considered a reasonable response to a powerful provocation. Laws exonerating men from killing adulterous wives are found worldwide and throughout human history. (Buss 2003:129)

A man’s response to signs of his partner’s infidelity in an intimate relationship seems general the world over: anger and aggression, an attempt to suppress the behavior by threatening, beating, isolating, and sometimes murdering the woman. (Trivers 2011:101)

In some parts of the United States, the very sight of adultery was, until very recently, considered sufficient justification for murder… sexual jealousy is the second or third leading cause of murders, and in many societies it is the first. (Trivers 2011:102)

Men are, of course, prone to self-deception in evaluating their partner’s extra-pair activities. (Trivers 2011:103)

…betrayal often rests on a bed of lies, of willful deception that may have gone on for months or years. You have played your part in all of this, by believing the lies—often with active self-deception or at the very least with failure to show due diligence. (Trivers 2011:111)

But infidelity (like pregnancy) is not spread along a continuum. You are either are unfaithful or you are not… Perhaps you say to yourself, ‘‘What’s the appropriate reward for someone who has lied to me, disrespected me, and plundered from me for two years?’’ and strangulation comes to mind. (Trivers 2011:112)


…the complex emotion we call jealousy did not arise from capitalism, patriarchy, culture, socialization, media, character defects, or neurosis. (Buss 2000:35)

Jealousy evolved as a primary defense, a co-evolved response to threats of a partner’s infidelity and abandonment. It becomes activated whenever a person perceives signs of defection—a strange scene, a sudden change in sexual behavior, a suspicious absence. It gets triggered when a partner holds eye contact with someone else for a split second too long, or when a rival stands a tad too close to your loved one or suddenly seems fascinated by the minutiae of his or her life. These signals do not inevitably mean that a partner will stray, just as the annoying blare of a fire alarm does not inevitably mean that a fire is blazing. Alarms may be false. But these signals alert us to the possibility of infidelity, since they have been statistically linked with relationship loss over the long course of human evolutionary history. (Buss 2000:45)

Co-evolution continues. Concealment, which evolved as a response to a partner’s jealousy, now produces an increased sensitivity to subtle signs of treachery. Jealousy becomes more easily activated. (Buss 2000:46)

Women have developed a strategy of intentionally evoking jealousy by strategically flirting with other men in their partner’s presence. Why trip an emotional switch and risk jealous violence? First, by evoking jealousy, women increase the man’s perception of their desirability. … Second, evoking jealousy provides a litmus test for the woman. By gauging the partner’s response, she can evaluate the strength of his commitment. (Buss 2000:47)

Ancestral people who became enraged at signs of their mate’s potential defection and who acted to prevent it had a selective advantage over those who were not jealous. People who failed to prevent infidelity in a mate had less reproductive success. (Buss 2003:10)

…a jealous man might follow his wife when she goes out, call her unexpectedly to see whether she is where she said she would be, keep an eye on her at a party, or read her mail. These actions represent vigilance. (Buss 2003:11)

Men and women admitted to equal amounts of jealousy, confirming that both sexes experience jealousy and overall do not differ in the intensity of their jealous feelings. … Seventeen of the women chose infidelity over either resources or time as the jealousy-inducing event, whereas only three women chose sexual infidelity. In marked contrast, sixteen of the twenty men chose sexual infidelity as the jealousy-inducing event, and only four men chose the diversion of time or resources. This study provides the first clue that, although both men and women have the psychological mechanism of jealousy, it is triggered by different events, which correspond to the adaptive problems of ensuring paternity for men and ensuring resources and commitment for women. (Buss 2003:127)

There are no cultures in which men are not sexually jealous. (Buss 2003:139)

Mate choice

Nowhere do people have an equal desire for all members of the opposite sex. Everywhere some potential mates are preferred, others shunned. (Buss 2008:106)

One difference is that sexual selection through mate choice can be much more intelligent than natural selection. …one of the main reasons why mate choice evolves is to help animals choose sexual partners who carry good genes. (Miller 2001:9)

…whereas natural and artificial selection can apply equally well to mushrooms, lemon trees, and oysters, Darwin believed that sexual selection acts most strongly in the higher animals. This is because courtship behavior and selective mate choice behavior are best carried out by mobile animals with eyes, ears, and nervous systems. The mate choice mechanisms that drive sexual selection are much more similar to artificial selection by humans than to blind forms of natural selection by physical or ecological environments. (Miller 2001:39)

Darwin’s notion that mate choice could shape organic form was without scientific precedent. (Miller 2001:45)

Throughout this book I have stressed the importance of mutual mate choice in human evolution. Human courtship means, above all, men and women talking to one another. It is not restricted to men standing up and pouring forth a stream-of-consciousness verbal display to anyone who will listen. (Miller 2001:376)

The attractive forms of novelty tend to rely on a uniquely human trick: the creative recombination of learned symbolic elements (e.g. words, notes, movements, visual symbols) to produce novel arrangements with new emergent meanings (e.g. stories, melodies, dances, paintings). This trick allows human courtship displays not just to tickle another’s senses, but to create new ideas and emotions right inside their minds, where they will most influence mate choice. Scheherazade did not produce a random series of nonsense words to play upon the sultan’s neophilia. She took existing words that already had a meaning, and put them together in new combinations that evoked new characters, plots, and images. (Miller 2001:413)

Animals have been playing God ever since they first evolved powers of sexual choice. Finding mates with good genes is one of the major functions of mate choice. Every female insect, bird, or mammal that selects a male based on fitness indicators is engaging in a form of genetic screening. (Miller 2001:431)

Mate choice is intrinsically discriminatory and judgmental, built to rank potential mates by reducing their rich subjectivity to a crass list of physical, mental, and social features. … The better we understand our mate choice instincts, the easier they may be to override when they are socially inappropriate. There is much more to modern human social life than courtship, and much more to people than their fitness indicators. (Miller 2001:432)

Mate preferences

The evolution of the female preference for males offering resources may be the most ancient and pervasive basis for female choice in the animal kingdom. (Buss 2008:110)

But women needed cues to signal a man’s possession of those resources. (Buss 2008:111)

Women worldwide desired financial resources in a marriage partner more than men. These findings provided the first extensive cross-cultural evidence supporting the evolutionary basis for the psychology of human mating. (Buss 2008:113)

The enormous body of empirical evidence… supports the hypothesis that women have evolved a powerful preference for long-term mates with the ability to provide resources. Because ancestral women faced the tremendous burdens of internal fertilization, a nine-month gestation, and lactation, they would have benefited tremendously by selecting mates who possessed resources. (Buss 2008:115)


Nothing lies closer to the reproductive engine of the evolutionary process. Those who fail to mate fail to become ancestors. Each living human, therefore, has descended from a long and unbroken line of successful mateships stretching back millions of years. If any one of our ancestors had failed to traverse the complex hurdles posed by mating, we would not be alive to ponder these improbable feats. Our mating minds—the glory of romance, the flush of passion, the triumph of love—are fortunate products of this evolutionary process. (Buss 2003:vi)

Discord and dissolution in mating relationships are typically seen as signs of failure. They are regarded as distortions or perversions of the natural state of married life. They are are thought to signal personal inadequacy, immaturity, neurosis, failure of will, or simply poor judgment in the choice of a mate. This view is radically wrong. Conflict in mating is the norm and not the exception. (Buss 2003:1)

Our failure to understand the real and paradoxical nature of human mating is costly, both scientifically and socially. (Buss 2003:2)

Darwin’s theory of sexual selection begins to explain mating behavior by identifying two key processes by which evolutionary change can occur: preferences for a mate and competition for a mate. (Buss 2003:3)

Whereas modern conditions of mating differ from ancestral conditions, the same sexual strategies operate with unbridled force. Our evolved psychology of mating remains. It is the only mating psychology we have; it just gets played out in a modern environment. (Buss 2003:14)

Conflict, competition, and manipulation also pervade human mating, and we must lift our collective heads from the sand to see them if we are to understand life’s most engrossing relationships. (Buss 2003:18)

Although the phylogenetic distance between humans and insects is vast, the basic adaptive logic behind holding on to a mate shows striking parallels. Males in both cases strive to inseminate females and to prevent cuckoldry. Females in both cases strive to secure investments in return for sexual access. But human tactics to retain a mate take on uniquely intricate forms of psychological manipulation which set them apart from the rest of the animal kingdom. (Buss 2003:124–25)


Finally, males place a value on female sexual monogamy (never mind their own tendencies). …men (compared with women) place relatively greater emphasis on short-term mating relations than on long-term. (Trivers 2011:99)

…this theory of the origin of modern institutionalized monogamy is an example of what Darwinism has to offer historians. (Wright 1995:99)

Natural selection

…natural selection works as if it were consciously designing organisms… (Wright 1995:35)

Paternity uncertainty

…virginity ensures paternity… (Bering 2010:71)

Cryptic female ovulation obscures a woman’s reproductive status. … Cryptic ovulation created a special adaptive problem for men by decreasing the certainty of their paternity. … Ancestral men, therefore, were faced with a unique paternity problem not faced by other primate males—how to be certain of their paternity when ovulation was concealed. (Buss 2003:66)

Whenever males contribute to their offspring, they confront the problem of uncertain paternity. This problem occurs whenever fertilization and gestation occur inside the female’s body, and it becomes exacerbated whenever males invest in offspring after they are born. Compared with many other male mammals men invest tremendously in their offspring. Cuckoldry is therefore a serious adaptive problem that men throughout human evolutionary history have had to solve. (Buss 2003:125)

Shahriyar’s fear of being cuckolded reflects what biologists call ‘paternity uncertainty’: the male never knows for sure whether a female is being sexually faithful, and therefore whether his alleged children actually carry his genes. (Miller 2001:385)


By ‘‘proprietary,’’ we mean first that men lay claim to particular women as songbirds lay claim to territories, as lions lay claim to a kill, or as people of both sexes lay claim to valuables. … Proprietariness has the further implication, possibly peculiar to the human case, of a sense of right or entitlement. Trespass by rivals provokes not only hostility but a feeling of grievance, a state of mind that apparently serves a more broadly social function. Whereas hostile feelings motivate action against one’s rivals, grievance motivates appeals to other interested persons to recognize the trespass as a wrong against the property holder and hence as a justification for individual retaliation or a grounds for more collective sanctions. (Wilson and Daly in Barkow et al. 1992:289)


Our logic also applies with special force to family and sexual interactions… each involving both conflict and cooperation over reproduction, life’s key aim. (Trivers 2011:5)

Reproductive value

Men cannot observe a woman’s reproductive value directly, and so selection could only have fashioned preferences in men for qualities that are correlated with reproductive value. (Buss 2008:140)

Reproductive value refers to the number of children a person of a given age and sex is likely to have in the future. … Reproductive value differs from fertility, which is defined as actual reproductive performance, measured by the number of viable offspring produced. (Buss 2008:141)

Youth is a critical cue because a woman’s reproductive value declines steadily as she moves past age twenty. (Buss 2008:142)


Because sex is one of the most valuable reproductive resources women can offer, they have evolved psychological mechanisms that cause them to resist giving it away indiscriminately. Requiring love, sincerity, and kindness is a way of securing a commitment of resources commensurate with the value of the resource that women give to men. (Buss 2003:45)

You know “that look” women get when they want sex? Me neither. (Steve Martin in Hurley et al. 2011:34)

Sex cells

Put simply, males in most species have a much greater reproductive interest in the quantity of their offspring, females in their quality… Indeed, it’s the fact of creating the larger sex cells that defines females as distinct from males. (Seabright 2012:12)

The tango between the selectivity of females and the persistence of males has taken even more elaborate and often more delicate forms in Homo sapiens than in these other species. The power of this simple logic is extraordinary. From one basic difference in cellular architecture between the sex cells of males and females—one large and scarce, the other tiny and abundant—and from the asymmetry in investments that males and females consequently make in gestation and parental care, think of all that has followed: the Trojan War, the Roman empire, the sonnets of Shakespeare, perhaps even the whole of our human civilization… (Seabright 2012:14)

…every man and woman alive today has emotions and perceptions that are shaped in part by the simple and natural asymmetry between sperm and eggs. (Seabright 2012:15)

Sex differences

Men’s greater preference for physically attractive mates is among the most consistently documented psychological sex differences. … Men’s preference for physically attractive mates is a species-wide psychological mechanism that transcends culture. (Buss 2003:58)

Men and women are alert to deception at the hands of the opposite sex. Women hold out sexually, require the demonstration of honorable intentions and commitments, and penetrate possible deceptions to discover hidden commitments. Men conceal their emotions, disguise their external commitments, and remain uncommunicative and noncommittal. They try to abscond with the sexual benefit without paying the cost of commitment. (Buss 2003:122)

While the lifetime reproductive success of a male is potentially almost unlimited, that of females is limited by the time necessary for pregnancy and lactation. Competition between males for females is therefore stronger than that between females for males, and males tend to be larger and stronger. Male aggressiveness and assertiveness have therefore been selected for. (Hinde 2008:43)

…extra-pair mating by a man involves little material disadvantage to his wife, providing he does not expend their resources on other women. In harmony with this, men are allowed more sexual licence than women in virtually all, and perhaps all, societies. Women are expected to be chaste and faithful. (Hinde 2008:43–44)

Throughout our evolutionary history, women’s sexual psychology has been shaped by the need to be selective in their reactions to men, just as men’s has been shaped by the need to be persistent in their approaches to women. (Seabright 2012:16)

Sexual selection

The evolution of characteristics because of their reproductive benefits, rather than survival benefits, is known as sexual selection. (Buss 2003:2–3)

Darwin’s theory of sexual selection begins to explain mating behavior by identifying two key processes by which evolutionary change can occur: preferences for a mate and competition for a mate. (Buss 2003:3)

One way to put it is Darwin’s way: ‘sexual selection’. But another way… is ‘selective breeding by females of males’. (Dawkins 2009:54)

Sexual selection was not only atheism, but it was indecent atheism. (Miller 2001:46)

It’s worth emphasizing the importance of Darwin’s theory of sexual selection for explaining human diversity, because substantially divergent evolution between closely related populations is surprising unless those populations are physically isolated… (Seabright 2012:51–52)

…the signals and strategies that men and women use to play the game of sexual selection are just a sample of the signals and strategies that all individuals use to navigate the groups and coalitions that determine the fitness of members of a group-living primate species. (Seabright 2012:140)

Sexual selection is a nonobvious extension of his [Darwin’s] general theory that accounts for seeming exceptions to it… (Wright 1995:34)

…the gauging of a man’s commitment does seem to be part of human female psychology; and male psychology does seem inclined to sometimes encourage a false reading. … in a high-MPI species such as ours, where a female’s ideal is to monopolize her dream mate… competition with other females is inevitable. … high male parental investment makes sexual selection work in two directions at once. Not only have males evolved to compete for scarce female eggs; females have evolved to compete for scarce male investment. (Wright 1995:63)

The ultimate source of the danger is sexual selection among males. Men have long competed for access to the scarcer sexual resource, women. (Wright 1995:100)

…sexual selection, the variant of natural selection that has made males so combative… (Wright 1995:276)

Sexual strategies

Sexual strategies do not require conscious planning or awareness. Our sweat glands are “strategies” for accomplishing the goal of thermal regulation, but they require conscious planning or awareness of the goal. Indeed, just as a piano player’s sudden awareness of her hands may impede performance, most human sexual strategies are best carried out without the awareness of the actor. (Buss 2003:6)

Although conflict between the sexes is pervasive, it is not inevitable. There are conditions that minimize conflict and produce harmony between the sexes. Knowledge of our evolved sexual strategies gives us tremendous power to better our own lives by choosing actions and contexts that activate some strategies and deactivate others. Indeed, understanding sexual strategies, including the cues that trigger them, is one step toward the reduction of conflict between men and women. (Buss 2003:13–14)

Sperm competition

…large testicle size is closely associated with mating systems in which females mate with multiple males. This is for the simple reason that if males have no realistic hope of monopolizing sexual access to females, it is in the reproductive interest of each male to ensure that his sperm is as abundant as possible in order to increase the probability that it fertilizes the females in preference to that of rival males (this process is called ‘‘sperm competition’’). (Seabright 2012:66)

Strategic interference

…many sources of conflict between the sexes can be traced to evolved differences in sexual strategies. …both sexes have evolved short-term and long-term mating strategies. But the nature of these strategies differs for the sexes. Men, far more than women, have evolved a deeper desire for sexual variety. This desire manifests itself in many forms, including sexual access sooner, more persistently, and more aggressively than women typically desire. Conversely, women have evolved to be more discriminating in short-term mating, typically delaying sexual intercourse beyond what men usually desire. Clearly, the sexes cannot simultaneously fulfill these conflicting sexual desires. This is an example of a phenomenon called strategic interference. … In sum, men and women come into conflict not because they are competing for the same resources, as occurs in same-sex strategic interference, but rather because the strategy of one sex can interfere with the strategy of the other. Sexual harassment is a form of strategic interference in the workplace. Deception on the dating scene is another form of strategic interference. (Buss 2008:323)

Tree of life

The classification was hierarchical: every living thing belonged to one species, every species belonged to one genus, and so on up through families, classes, orders, and phyla to the plant and animal kingdom, all in one tree of life. (Pinker 1997:324)

One of Darwin’s best arguments for evolution was that it explained why living things are hierarchically grouped. The tree of life is a family tree. (Pinker 1997:325)


…virginity ensures paternity… (Bering 2010:71)


And youth is a key ingredient in judging attractiveness: “Age is the monster figure of the gay world.” (Buss 2003:62)

Youth is a critical cue because a woman’s reproductive value declines steadily as she moves past age twenty. … Without exception, in every one of the thirty-seven societies examined in an international study on mate selection, men preferred younger wives. (Buss 2008:142)

…men desire young women because over evolutionary time youth has consistently been linked to fertility. (Buss 2008:144)

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