Download Precis of `The Mating Mind` By Geoffrey Miller Published as: Miller

Precis of ‘The Mating Mind’
By Geoffrey Miller
Published as:
Miller, G. F. (2001). Precis of ‘The Mating Mind’. Psycoloquy 12(008).
http://www.cogsci.ecs.soton.ac.uk/cgi/psyc/newpsy?12.008
Abstract
'The mating mind' revives and extends Darwin's suggestion that sexual selection through mate
choice was important in human mental evolution - especially the more 'self-expressive' aspects
of human behavior, such as art, morality, language, and creativity. Their 'survival value' has
proven elusive, but their adaptive design features suggest they evolved through mutual mate
choice, in both sexes, to advertise intelligence, creativity, moral character, and heritable fitness.
The supporting evidence includes human mate preferences, courtship behavior, behavior
genetics, psychometrics, and life history patterns. The theory makes many testable predictions,
and sheds new light on human cognition, motivation, communication, sexuality, and culture.
I. CHAPTER 1: CENTRAL PARK (US edition)/EXHIBITION ROAD (UK edition).
1. The human mind evolved somehow. Yet it remains unclear what selection pressures favored
our large brains, our creative intelligence, and our unique capacities for language, art, music,
humor, romantic love, and moral commitment. Following Herbert Spencer's misleading phrase
'the survival of the fittest', most theorists throughout the last 140 years have tried and failed to
identify the 'survival value' of these capacities.
2. 'The mating mind' suggests that if one meta-theory doesn't work, we should try another one.
Darwin (1871) argued that sexual selection (for reproduction) is distinct from natural selection
(for survival), and that traits inexplicable in terms of 'survival value' can often be explained as
ornaments for attracting sexual partners. The revival of sexual selection theory since about
1980 has confirmed the utility of Darwin's distinction between natural and sexual selection.
Sexual selection often creates an evolutionary positive-feedback loop that is highly sensitive to
initial conditions. It therefore tends to produce extravagant traits that have high costs and
complexity, yet these traits are often unique to one species, and absent in closely-related taxa.
By contrast, natural selection for ecological utility tends to produce convergent evolution, where
many lineages independently evolve the same, efficient, low-cost solutions to the same
environmental problems.
3. Viewed from a macro-evolutionary perspective, the human brain fits this profile of sexuallyselected ornaments: it is unique among living primates, has high metabolic costs and enormous
complexity, and its capacities are conspicuously displayed during courtship (especially verbal
courtship). The brain's low level of sexual dimorphism is congruent with evidence that human
mate choice is mutual, with males and females almost equally choosy about the mental traits of
long- term sexual partners. Sexual dimorphism is a distinctive outcome of sexual selection, but
sexual selection does not always produce dimorphism.
4. Mate choice suffices to explain many distinctive aspects of the human mind, especially those
that yield no apparent survival benefits. Darwin (1871) made the same argument in suggesting
that human language and music evolved, like bird song, for courtship. This view of the mind as
a set of courtship adaptations can now be extended and refined in the light of modern sexual
selection theory, evolutionary psychology, and evolutionary anthropology. Although evolutionary
psychology recognizes the powerful role of sexual selection in shaping sex differences in
motivation, emotion, and cognition, it has neglected the possibility that sexual selection could
produce psychological adaptations (such as language and creativity) equally in both sexes.
5. Many researchers have suggested that human mental evolution was so fast and unusual that
it must have been driven by some sort of positive-feedback process. Other candidates for the
positive-feedback process have included gene-culture co-evolution, inter-tribal warfare, and
social selection for Machiavellian intelligence. Sexual selection has been strangely neglected,
though it is the best-established, most powerful form of positive-feedback evolution known to
biologists.
6. Evolutionary psychology has tended to overlook sexually-selected mental traits because its
criteria for recognizing psychological adaptations (e.g. efficiency, modularity, low heritability,
universality across individuals) have been too restrictive (Miller, 2000). Sexual ornaments
violate the efficiency criterion because they have high growth, maintenance, and display costs
precisely so they can function as reliable fitness indicators according to Zahavi's (1975)
handicap principle. They are only somewhat modular at the genetic, developmental, and
metabolic levels, because total modularity would render them totally useless as indicators of
general health and fitness. Ornament quality tends to have moderate to high heritability,
because ornaments often evolve to advertise heritable genetic quality. Likewise, the whole point
of sexual ornaments is to amplify apparent individual differences, so they show extreme
variability rather than uniformity across individuals. Unfortunately, some evolutionary
psychologists such as Pinker (1997) have dismissed music, art, humor, and general intelligence
as non-adaptations because they did not fit the typical profile of survival-selected adaptations -hardly surprising, if they were sexually selected.
7. In other respects, 'The mating mind' is standard biological adaptationism, focusing much
more on 'what' and 'why' than on 'how', 'when', or 'where'. It makes very few claims about the
geographical location, antiquity, or genetic changes associated with the evolution of our
sexually-selected mental traits. The emphasis, as in most animal behavior research, is on
characterizing various adaptations and seeing whether their features are consistent with
particular selection pressures hypothesized to have produced them. The book's theory of
mental evolution is more testable than most, because the heritable sexual preferences of our
ancestors are probably still manifest in modern mate choice, so they can be assessed as
selection pressures independently of the courtship adaptations they are posited to have favored.
II. CHAPTER 2: DARWIN'S PRODIGY.
8. This chapter reviews the peculiar history of Darwin's theory of sexual selection through mate
choice, tracing its rejection by Victorian biologists, its neglect for over a century, and its dramatic
revival in the last couple of decades (also see Cronin, 1991).
9. Charles Darwin, like his grandfather Erasmus, recognized that sexual reproduction was
central to evolution. His theory of sexual selection was developed not so much to explain sex
differences, but to account for complex ornaments that seem useless for survival, and therefore
inexplicable through natural selection. He suggested that if animals of a species came to prefer
a particular trait when choosing sexual partners, that trait would tend to grow in size, complexity,
and quality over evolutionary time, even if the trait had high costs in every other domain of
evolutionary competition.
10. Darwin (1871) had a sophisticated view of the psychology of mate choice. He emphasized
that even relatively simple nervous systems (e.g. insects, fish, frogs) suffice for mate choice -but that the more complex an animal's brain, the more intelligent its mate choice could be. As
mental complexity increased, the discriminatory power of mate choice would increase, so sexual
selection would command ever greater importance in evolution, reaching its zenith in human
evolution. DARWIN noted "He who admits the principle of sexual selection will be led to the
remarkable conclusion that the cerebral system not only regulates most of the existing functions
of the body, but has indirectly influenced the progressive development [i.e. evolution] of various
bodily structures and of certain mental qualities." He did not attempt a one-way reduction of
psychology to biology, but saw psychology as a driving force in biological evolution.
11. Whereas Darwin's natural selection theory was widely accepted, his idea of sexual selection
through mate choice was almost universally rejected by Victorian biologists. Alfred Wallace was
a leading critic, suggesting that most male ornamentation was a developmental side-effect of
greater male energy and physiological exuberance. Wallace's objections led mate choice theory
to be viewed for the next hundred years as Darwin's most embarrassing blunder. This sceptical
view of mate choice was reinforced by leading biologists of the early 20th century, including
Thomas Hunt Morgan, Julian Huxley, J.B.S. Haldane, and Ernst Mayr. They combined a groupselectionist, good-of-the-species abhorrence of survival-reducing ornamentation with a
Modernist machine aesthetic (derived from the Bauhaus and other puritanical sects of
socialism), which viewed ornamentation as morally decadent, economically oppressive, and
tasteless.
12. As a result, almost all of 20th century psychology, anthropology, neuroscience, and the
humanities developed without recognizing any role for mate choice in human mental evolution.
Instead, Freud's paleolithic fantasies dominated views of prehistoric sexuality, and his theory of
excess libido being sublimated into artistic creativity echoed Wallace's surplus-energy
arguments for ornamentation. This bias against mate choice theory began to erode only in the
1970s, leading to a runaway revival of mate choice theory in evolutionary biology, to the point
that animal behavior journals are now dominated by experiments on mate choice and sexual
competition. Yet this revival has gone largely unnoticed in mainstream psychology,
neuroscience, and the social sciences, which still view 'survival of the fittest' as evolution's
bottom line, and which therefore have trouble seeing any evolutionary rationale for those
aspects of human nature most concerned with self-ornamentation, display, status, ideology,
fashion, and aesthetics.
III. CHAPTER 3: THE RUNAWAY BRAIN.
13. This chapter considers the possibility that runaway sexual selection drove the rapid
escalation of brain size characteristic of our lineage, but it ultimately rejects this 'runaway brain'
theory as neglecting the role of mutual mate choice, and failing to explain the sexual equality in
human brain size and intelligence.
14. Ronald Fisher (1930) suggested that sexual selection through mate choice could lead to a
positive-feedback process, in which ever-more- discriminating sexual preferences become
genetically linked to ever- more-extravagant sexual displays. The runaway hypothesis was
neglected for fifty years, until biologists developed mathematical models in the early 1980s
showing that Fisher was right. Heritable sexual preferences will tend to become genetically
correlated with the sexual ornaments that they favor, and this genetic correlation gives the
runaway process its evolutionary momentum. The direction of runaway is so sensitive to initial
evolutionary conditions that it is very hard to predict which sexual ornaments will evolve in a
lineage, but once underway, runaway will tend to increase the complexity and magnitude of the
favored ornament to extremes. Runaway's unpredictability can explain why closely related
species can differ so dramatically in their ornamentation and courtship behavior.
15. In previous work (Miller, 1993), I suggested that human mental evolution was driven by
runaway sexual selection. If hominid females happened to develop a sexual preference for
creative intelligence, then males with more creative intelligence would attract more sexual
partners and would produce more offspring. Those offspring would inherit both the taste for
clever courtship and the capacity for producing it. Over many generations, average creative
intelligence in the lineage would increase rapidly, perhaps explaining why brain size tripled in
just two million years.
16. This 'runaway brain theory' could explain the speed of encephalization, the rarity of creative
intelligence across species, and people's propensity to show off their creativity and intelligence
in sexual courtship. However, the theory predicts large sex differences in brain size and creative
intelligence, and neuroanatomical and psychometric evidence shows these differences are very
small. Male human brains are only about 100 cubic centimeters larger than female brains (after
allometrically correcting for body size differences), and there is no apparent sex difference in the
g factor that underlies IQ test performance. Males do account for a large proportion of public
cultural displays in every known society, such as the invention and dissemination of art, music,
ideologies, religions, philosophies, and science (Miller, 1999). But this cultural dimorphism might
be conflated with Holocene patriarchal cultural traditions.
17. The lack of sex differences in human mental capacities is a strong argument against the
runaway brain theory. This does not imply that sexual selection is irrelevant, only that the
choosy-female, displaying-male model assumed by Fisher (1930) is too simple for the human
case, in which both sexes are choosy (at least in establishing long-term relationships), and both
display their mental traits during courtship. If sexual selection drove human mental evolution, it
must have been a form of sexual selection that could work given mutual mate choice.
IV. CHAPTER 4: A MIND FIT FOR MATING.
18. This chapter introduces the idea of sexual ornaments as costly, reliable indicators of fitness,
and argues that our most distinctive mental traits evolved through mutual mate choice as
fitness-indicators.
19. Many biologists believe sexual reproduction evolved as a way to minimize the disruption
caused by the copying errors and mutations intrinsic to DNA-based reproduction. By extension,
mate choice can be viewed as a method for enhancing this anti-mutation effect, by favoring
sexual partners who carry 'good genes' (i.e. genotypes with a low number of deleterious
mutations). Mate choice for good genes will tend to focus on the observable traits of potential
mates that best reveal their mutation load. Therefore, traits that happen to reveal mutation load
more accurately than other traits (e.g. through more complex development that requires the
interaction of more genes) will tend to be favored in mate choice. Under sexual selection, such
traits will tend to grow ever larger, costlier, and more complex, so they function as ever more
reliable indicators of good genes. Insofar as genetic quality implies expected evolutionary
fitness, these sexually-selected traits could be called 'fitness indicators'.
20. Human brains make particularly good fitness indicators because their growth depends on
about half the genes in the genome, thereby summarizing a huge amount of information about
mutation load. Brains are also good indicators of nutritional state and general health, because
they have such high energetic costs, constituting only 2% of body weight, but consuming over
25% of adult metabolic energy (60% in infancy). Moreover, the more important brains became
during primate evolution (for whatever reason), the more incentive mate choice would have had
to focus on specific indicators of brain quality (i.e. mental fitness as distinct from physical
fitness).
21. Fitness indicator theory raises evolutionary-genetic issues about the heritability of fitness.
Throughout the 1980s, many biologists were skeptical about 'good genes' models of sexual
selection because such models assumed fitness would remain heritable across many
generations. Yet Fisher's (1930) 'fundamental theorem of natural selection' implied that
selection should decrease genetic variance, driving disfavoured alleles to extinction, thereby
decreasing the heritability of fitness to zero at evolutionary equilibrium. The 'heritability of
fitness' debate continued today, but evidence is accumulating that fitness remains heritable in
many species much of the time, probably through a combination of ever-changing selection
pressures (e.g. geographic diversity of habitats plus migration, and host-parasite co-evolution),
and ever-recurring deleterious mutations. The remainder of the book takes for granted the
heritability of a general 'fitness factor' (analogous to, and superordinate to, the g factor) in
humans, though much more research needs to be done to demonstrate such a fitness factor
(see Miller, in press). Recent genetic analyses suggest that at least 1.6 harmful new mutations
per individual per generation have been arising in our lineage for the last several million years
(Eyre-Walker & Keightley, 1999). This probably exceeds the mutation rate that natural selection
could contain in the absence of sexual selection for genetic quality.
22. Fitness indicators also raise reliability issues: what keeps low- fitness individuals from
cheating by displaying the high-quality ornament? Economists working on 'signalling theory' (a
branch of game theory) showed in the 1960s that when there are incentives for deception,
signals of quality or intention must be costly in order to be reliable. This point was independently
applied to animal signalling, especially sexual ornaments, by Amotz Zahavi (1975), with his
'handicap principle'. In his view, mate preferences should only favor sexual ornaments that have
such high marginal costs that low-fitness pretenders could not afford to display a high-quality
form of the ornament. Sick, starving, inbred peacocks cannot afford to grow large tails, for
example, and this makes a large peacock tail as reliable fitness- indicator. If peacock tail size
was uncorrelated with general fitness, peahens would soon lose the sexual preference for such
an uninformative ornament. The handicap principle was vigorously debated for twenty years in
biology, in ignorance of the economic game theory work. Only recently have biologists started to
accept that prodigious, survival-reducing waste is a necessary feature of most sexual
ornaments, in order to keep them reliable as fitness indicators.
23. In some cases, however, ornaments can function as direct 'indexes' of fitness, reliably
revealing an individual's fitness without imposing high survival costs. Indexes depend on the
existence of some intrinsic genetic or developmental correlation between fitness and ornament
quality. Human intelligence is likely to be a fitness index, whereas art, music, and humor are
more likely to be fitness-indicating handicaps (unfortunately, the book did not make this
distinction very clear).
24. The book argues that our most distinctive psychological adaptations evolved mostly through
mutual sexual selection as fitness indicators. Of course, these species-unique courtship
adaptations are far out- numbered by the psychological adaptations for social intelligence,
foraging, predator avoidance, etc. shared with other primates. Yet we still need some
explanation of why small, efficient, ape-sized brains evolved into huge, energy-hungry
handicaps spewing out useless luxury behaviors such as flirtatious conversation, music, and art.
V. CHAPTER V: ORNAMENTAL GENIUS.
25. This chapter examines how psychological biases (including sensory, perceptual, cognitive,
and emotional attunement to certain stimuli) influence mate choice and hence the design of
sexual ornaments. It then makes some analogies between courtship and marketing, and
between sexual selection and venture capital, and considers the possible interactions during
mental evolution between runaway sexual selection, sexual selection for fitness indicators, and
psychological biases.
26. Mate choice is mediated by the senses and the mind. Both include a large number of
'biases' or selective sensitivities that are evolutionarily contingent outcomes of their design
details, or of adaptation to certain environmental conditions. Biologists can sometimes predict
which stimuli will excite a perceptual system that evolved to detect certain biologically relevant
objects and events, but (as ethologists realized in the 1950s) it is often hard to predict which
artificial super-stimuli might excite the system even more. Many sexual ornaments may have
originated as accidental super-stimuli (arising from novel mutations) that just happened to
attract the attention of the opposite sex given how their perceptual systems work. Since the
super-stimulus sensitivities are often evolutionarily contingent, the design of the sexual
ornaments that they favor may be evolutionarily contingent as well. This is yet another reason
why sexual selection is an unpredictable, diversifying process that rarely happens the same way
twice.
27. As Darwin (1871) realized, the psychological biases affecting mate choice are not restricted
to low-level perception, but can include propensities for novelty-seeking and pleasure-seeking.
Given that primates are unusually neophilic and derive pleasure from social interaction, these
cognitive and motivational biases may have led mate choice to favor more creative courtship
with more social content during hominid evolution.
28. Any given sexual ornament, including the human mind, probably evolved through some
combination of runaway sexual selection, sexual selection for fitness indicators, and
psychological biases that happened to favor certain details of ornament design. The interaction
of these three sexual selection principles also helps to explain the mechanisms of speciation,
the proliferation of biodiversity, and the origins of evolutionary innovations. Sexual selection
works like venture capital, extending a line of reproductive credit to potentially useful
evolutionary innovations before they show any ecological profitability. This may help to explain
hominid encephalization before significant signs of any cultural or technological progress. The
obsession with survival selection is analogous to the early 20th century corporate obsession
with production as opposed to marketing and advertising. Business had its 'marketing revolution'
in the last half century; it is time for evolutionary psychology to recognize that creative social
behavior is to the opposite sex what products are to consumers.
VI. CHAPTER 6: COURTSHIP IN THE PLEISTOCENE.
29. This chapter reconstructs Pleistocene hominid mating patterns using a variety of evidence,
and identifies the opportunities for mate choice to have influenced reproductive success in small
groups of hunter- gatherers.
30. Popular culture images of prehistory sustain the myth of rapacious, unchoosy cave-men and
helpless, unchoosy cave-women. Likewise, early primatology suggested that 'alpha males'
attained the 'right to mate' with all females in a group. More recent studies of human tribal
societies and of other primates suggests these views are wrong, and that both sexes exercise
mate choice among chimpanzees, bonobos, and tribal humans, which are all characterized by
multi-male, multi-female social groups. Other evidence (ranging from comparative morphology
to evolutionary psychology) suggests that hominids were not lifelong monogamists, but followed
a pattern of serial social monogamy (with relationships lasting a few days to a few years)
augmented by extra- pair copulations and some polygyny. Rapists would have been ostracized
or killed, and these costs would have usually exceeded the reproductive benefits of a single
copulation, given concealed ovulation.
31. It remains unclear how much paternal investment there was, as opposed to step-parental
investment functioning as a kind of altruistic courtship display. Data suggesting that women
favor self-confident, high-status men may reveal a preference for high heritable fitness, rather
than an expectation of long-term paternal investment. Given that most individuals would have
had their first child by their early 20s, and sought additional mates thereafter, there must have
been considerable overlap between parenting and courtship -- stories told to children while
within earshot of a potential mate may have functioned more as courtship displays than as
parental investment. Conversely, the mate choices of adult females (i.e. mothers) may have
been influenced by the preferences of their children regarding which prospective step-father
appeared kinder and more entertaining. Given frequent interaction with kin, mate choice may
have also worked as a distributed decision-making process, taking into account the collective
wisdom of parents, siblings, and offspring. Equally, if individuals were choosing for heritable
fitness, kin of all ages would have had incentives to advertise their own fitness on behalf of their
fertile relatives, giving rise to various collective courtship rituals in which kin groups show off to
other kin groups. Even 'arranged marriages' impose sexual selection, if the parents are using
consistent mate choice criteria on behalf of their children (who may inherit the same
preferences).
32. A key section discusses a 'fitness matching' model of mutual choice for fitness affordances,
based on game theory models of 'two- sided matching'. The model posits a mating market in
which individuals assortatively mate for indicators of heritable fitness, and those indicators
evolve through an interaction between parental mate choice and survival selection on offspring.
Surprisingly, fitness matching can drive the evolution of elaborate courtship behavior even
under the limiting case of strict lifelong monogamy. Fitness matching also maximizes the
genetic variance in fitness in the next generation, giving natural selection more raw material on
which to work. The fitness matching process automatically generates sexual equality in
courtship adaptations. Such sexually-selected adaptations with no sexual dimorphism have
usually been dismissed as 'species recognition markers' by biologists, though they are
displayed in the courtship of many species. Fitness matching based on creative courtship
behavior may have been the key sexual selection process in human mental evolution.
VII. CHAPTER 7: BODIES OF EVIDENCE.
33. This chapter examines human morphological features that evolved under mate choice,
especially features that reveal mutual choice. These physical traits can work as metaphors for
sexually-selected mental traits, as both fitness indicators and aesthetic ornaments resulting from
runaway and perceptual biases.
34. Male human beards, penises, and upper-body muscles, and female breasts, buttocks, and
orgasmic capacities, show evidence of evolving through sexual selection. There are also some
monomorphic traits such as long head hair, hairless skin, highly expressive faces, and full lips
that function as sexual attractants. These fleshy parts don't fossilize, and so have been
somewhat neglected in human evolution theorizing. However, all these traits are valued in
modern mate choice, are displayed during courtship, and are mostly unique to humans. Also,
the dimorphic traits develop fully only during puberty, in time for sexual attraction. These criteria
also apply to many mental traits.
35. The chapter concludes by discussing how sexual selection shaped the evolution of physical
and mental capacities for playing sports, which function as non-lethal domains of sexual
competition.
VIII. CHAPTER 8: ARTS OF SEDUCTION.
36. The last four chapters offer four case studies of uniquely human mental traits that appear to
have evolved under mate choice: art, morality, language, and creativity. This chapter considers
body ornamentation, art, and aesthetics.
37. Art is an easy example because no one has posited a credible survival function for art,
whereas it has obvious analogues to the sexually-selected visual displays of other species such
as peacocks and bowerbirds. Male bowerbirds construct large ornamental bowers to attract
females, decorating them with brightly colored flowers, pebbles, shells, and feathers. Females
inspect multiple bowers, choose the one they find most attractive, and mate with its creator,
raising her brood in a separate, simple nest of her own construction. The bower is part of the
bowerbird's 'extended phenotype' -- a genetically evolved display constructed outside the body.
Human aesthetic behavior also functions as an extended phenotype, ranging from ochre
pigments applied on as skin decoration, to cave paintings and Venus figurines.
38. Human aesthetic preferences could have arisen (as mechanisms of mate choice for good
artisans) through runaway sexual selection, through sensory biases, and/or through selection as
fitness indicators. However, runaway can't make any predictions about which particular
preferences will evolve, and sensory bias theory doesn't work very well here because other
primates do not share the same aesthetic preferences as humans, despite sharing almost
identical visual systems. The idea that beautiful artefacts carry information about the fitness of
their makers makes more sense. Thorstein Veblen (1899) and Franz Boas (1955) insisted that
an artist's manifest virtuosity (manual skill, access to rare resources, creativity,
conscientiousness, intelligence) is the major criterion of beauty in most cultures. Their view was
eclipsed in aesthetic theory by 20th century Modernism (which rejected the concepts of beauty
and virtuosity), but remains relevant to most popular culture, interior design, folk art, craft, and
fashion. This beauty-as-virtuosity theory also helps make sense of the hand axe, which can be
viewed as a sexually-selected feature of hominid extended phenotypes for over 1.5 million
years.
IX. CHAPTER 9: VIRTUES OF GOOD BREEDING.
39. This chapter examines our sexual abhorrence of selfishness, cheating, and lying, and
suggests that mate choice shaped our distinctive human capacities for sympathy, kindness,
sexual fidelity, moral leadership, magnanimity, romantic gift-giving, and sportsmanship. It
suggests that sexual selection explains much of human altruism that cannot be explained
through kin selection or reciprocal altruism, and tries to take seriously David Buss's (1989)
finding that 'kindness' was the top-ranked, most-desired trait in a potential mate across all 37
cultures he studied.
40. All evolutionary theories of morality have to find a hidden genetic benefit to apparently
altruistic acts. Kin selection does it by pointing out that genetic benefits can be spread across
relatives by helping them, and reciprocal altruism theory does it by pointing out that benefits to
oneself can be spread across time, through repeated interactions with trusted trading partners.
These theories are good at explaining parental solicitude, nepotism, economic prudence, and
instincts for cheater-detection. However, they leave most of human morality unexplained.
Sexual selection provides a complementary way of explaining how selfish genes can give rise to
altruistic individuals.
41. Basically, the hidden genetic benefits of altruism could have been reproductive: conspicuous
magnanimity and other moral behaviors became sexually attractive because they were good
fitness indicators. Their reliability was guaranteed by the costs of altruism, under the handicap
principle. Only the fit could afford to be generous. Sexual selection can favor almost any degree
of generosity or heroism, despite their survival costs, just as it can favor almost any length of
peacock tail. Mate choice can work as a moral filter from each generation to the next.
42. The evolution of big-game hunting provides one example of sexual selection for
magnanimity. Kristen Hawkes (1991) has argued that male hunting of large, dangerous prey
evolved not to 'feed one's family' (monogamous nuclear families being rare in the Pleistocene),
but to attract multiple female partners, who appreciated hunting ability as a fitness indicator, and
as a direct nutritional benefit to themselves and their offspring. Anthropological data show that
good hunters have more extra-pair copulations than poor hunters.
43. The most complicated argument in the book concerns the evolution of moral displays
through an interaction between sexual selection for costly signals, and group selection among
alternative signalling equilibria. This relies on the recent evolutionary game theory research on
games with very large numbers of Nash equilibria. (At each equilibrium, by definition, all
individuals are acting rationally selfish -- the issue is which equilibrium will be favored by
evolution given competition between groups.) The argument is too intricate to outline here, but it
reaches the surprising conclusion that evolution can favor precisely those sexual display
equilibria that bring the highest group benefits, without any conflict between individual-level
selection and group-level selection (see Boyd & Richerson, 1990). The relevance to human
morality is that, given competition between groups, sexual preferences will evolve to favor
apparently altruistic capacities for sympathy, magnanimity, group leadership, and punishment of
cheaters -- rather than purely wasteful, non-altruistic displays such as the peacock's tail.
44. The chapter applies this logic to understand charitable behavior, male gift-giving during
courtship, the emotional capacities for sympathy and sexual fidelity, the sexual aversion to
psychopaths, the female preference for generous fathers and step-fathers, and the capacity for
sportsmanship (where cheating implies any behavior that lowers the meritocratic correlation
between a competitor's fitness and their success in the sport). It concludes by urging
evolutionary psychology to broaden its concept of human morality from what Nietzsche called
the Christian 'morality of the herd' (fairness, conscience, equality, fidelity, altruism), to what he
called the pagan virtues (e.g. bravery, beauty, skill, leadership, stoicism, sacrifice, good
manners).
X. CHAPTER 10: CYRANO AND SCHEHEREZADE.
45. This chapter addresses the evolution of language, emphasizing that if talking gives away
useful information to others, it raises the same evolutionary dilemma as altruism in general -- a
dilemma that, as with morality, can be resolved by reference to sexual selection.
46. The debates over language's innateness and uniqueness have been resolved in favor of
Steven Pinker's (1994) view that language is a uniquely human, genetically-based psychological
adaptation that evolved for some set of biological functions. The question remains: what
functions? Most theories of language evolution do not identify any specific selection pressures
in favor of communication ability, and those that stress survival benefits cannot explain why no
other species evolved such a supposedly useful ability. Moreover, most such theories fail to
explain the selfish genetic benefits from the apparently altruistic (information-giving) act of
speaking, and fail to explain why people compete to say things rather than to listen in group
conversations.
47. Almost all complex acoustic signals in other species evolved as courtship displays through
sexual selection: frog croaks, bird song, whale song, etc. Human verbal courtship (i.e.
conversation between lovers) serves an analogous function, with mutual advertisement of
capacities for speaking, listening, thinking, remembering, story-telling, and joke-making.
Assuming they spoke three words a second for two hours a day during courtship, with an
average of three months of sex before a viable pregnancy, the average hominid would have
uttered a million words of verbal courtship before reproducing. This million- word hurdle would
have given prospective mates ample opportunity to assess verbal ability, creativity, and
intelligence, and to reject dumb, boring mumblers. The importance of verbal courtship is
exemplified by the legends of Cyrano de Bergerac and Scheherezade, who provoked love
through their poetic and story-telling abilities.
48. In Turing's (1950) original 'imitation game', a male interrogator tries to determine whether he
is interacting via computer with a real woman, or a computer program that imitates a woman.
Turing assumed that verbal courtship (including capacities for making jokes and composing
poems) was the most challenging test for artificial intelligence, but this sexual-selection aspect
of the Turing test was stripped away by later AI researchers as an irrelevant distraction.
49. Once language evolved, much more of our mental life became subject to sexual selection.
Verbal courtship could reveal whole new areas of mental functioning -- personality, intelligence,
beliefs, desires, past experiences, future plans -- that are hidden in the more physical courtship
of other species. As language gave a clearer window on the mind, the mind became more easily
shaped by mate choice. This sexual selection feedback loop between mate choice, language
ability, and creative intelligence was probably the mainspring of human mental evolution.
50. A detailed analysis of vocabulary size provides a quantitative case study of how modern
human language exceeds any plausible demands of survival and social reciprocity. Our average
60,000 word vocabularies far exceed the 850-word vocabulary of the artificial language 'Basic
English', invented by I. A. Richards and C. K. Ogden in the 1920s. Basic English, like most
small-vocabulary pidgin languages, suffices for all ordinary aspects of trade, cooperative work,
and survival, including the exchange of threats, promises, warnings, and news. Biology and
astronomy textbooks have been written in Basic English. This suggests most of our words are
pragmatically redundant, and must be serving some self-advertisement function. Since
vocabulary size is highly correlated with general intelligence, and is highly heritable, it appears
to function as a reliable indicator of heritable mental fitness. People are generally unaware of
their sexual preferences for large vocabularies (rare is the personal ad asking for a partner who
knows 50,000 useless synonyms), but assortative mating for vocabulary size is higher than for
almost any other mental trait.
XI. CHAPTER 11: THE WIT TO WOO.
51. The final chapter explores how evolution can favor benignly unpredictable behavior,
suggests hominids developed sexual preferences for interesting, funny mates over boring
mates, and proposes that these sexual preferences for unpredictable courtship behavior drove
the evolution of human creativity.
52. The earliest game theorists such as John von Neumann recognized that many games
require 'mixed strategies' -- strategies that randomize moves from one play to the next.
Unpredictability often brings strategic advantages. With the theory of 'protean behavior',
biologists independently developed the same principle in considering anti-predator behavior: an
unusual appearance and unpredictable evasion movements could protect prey from being
noticed and captured. The unpredictability of animal behavior may reflect capacities for
adaptively protean behavior, more than some side-effect of neural noise or 'random error' (N. B.
analysis of variance, psychology's favorite statistical method, can't distinguish proteanism from
noise).
53. With the evolution of 'Machiavellian intelligence' (the capacity for predicting and
manipulating the social behavior of conspecifics), primates would have been under selection to
be socially unpredictable to their reproductive competitors (Miller, 1997). The unpredictability of
primate aggression noticed by field researchers probably reflects a mixed strategy. This sort of
'social proteanism' may have provided some genetic and neurological foundations for human
creativity, by endowing our brains with mechanisms for randomizing social behaviors in general,
which could be applied to the special case of courtship, to produce amusingly unpredictable
romantic behavior. Creativity could have been favored initially as a reliable indicator of social
proteanism ability, and of youthfulness, insofar as juvenile primates tend to be more playful and
unpredictable than adults. In modern humans, creativity is also correlated highly with general
intelligence, and moderately with health and energy level; its heritability appears to be a side
effect of its correlation with intelligence, which is highly heritable.
54. Creative courtship may have also played upon neophilia, a fundamental attentional and
cognitive attraction to novelty. In terms of the psychological bias theory of sexual selection,
neophilia is just another bias that might influence mate choice. Darwin (1871) argued that
neophilia was an important factor in the diversification and rapid evolution of bird song. Primate
and human neophilia is especially strong, with boredom often cited as a reason for terminating
sexual relationships. Partners who offered more cognitive variety and creativity in their
relationships may have had longer, more reproductively successful relationships -- as
symbolized, again, by Scheherezade. A good sense of humor is the most sexually attractive
variety of creativity, and human mental evolution is better imagined as a romantic comedy than
as a story of disaster, warfare, predation, and survival.
55. Sexual selection for creativity undermines some of the evolutionary epistemology claims
about the reliability of human knowledge. Whereas natural selection might tend to favor minds
with accurate, survival-enhancing world-models, sexual selection might favor minds prone to
inventing attractive, imaginative fantasies -- as long as fantasy-invention ability remains a
reliable fitness-indicator. (Brigham Young's religious visions revealed his imagination and
intelligence, and attracted his 27 wives, but that does not guarantee the veracity of his belief
that dead ancestors can be retroactively converted to Mormonism.) Sexual selection rarely
favors displays that include accurate representations of the world -- peacock tail eye-spots catch
attention by resembling eyes, but they are not very good likenesses. Likewise for human
ideologies: they may be sexually attractive be revealing an individual's character, intelligence,
and moral ideals, but they need not be good representations of reality. Sexual selection can
explain why most people prefer fiction to non-fiction, religious myth to scientific evidence, and
political correctness to intellectual coherence.
XII. EPILOGUE.
56. The epilogue lists the theory's limitations, emphasizing that it is not a complete theory of
mental evolution, only a theory of the more distinctive, display-oriented human capacities that
have proven hard to explain in 'survival value' terms. It admits that my ideas may have been
unduly influenced in some cases by my being male, and calls for further refinements by
researchers of both sexes. Without committing the 'naturalistic fallacy', it notes that debates
about moral values and social ideals can and should be informed by our concepts of human
nature and human evolution -- especially debates over educational policy, consumerism,
political philosophy, and bioethics. It calls for the conscious suppression of our instincts for
discriminatory mate choice in social contexts where such discrimination is inappropriate, and
concludes with a hint about how sexual selection may continue to shape human evolution in the
future.
XIII. THE THEORY'S LIMITATIONS AND WEAKNESSES AND FURTHER DIRECTIONS.
57. This final section goes beyond the book's contents somewhat to provide some clarifications
for Psycholoquy readers. First, the theory's limitations. 'The mating mind' offers a snap-shot of a
provisional theory under construction. It does not pretend to be a complete account of human
mental evolution, because it addresses only those psychological adaptations manifest in sexual
courtship. It accepts that natural selection and other forms of social selection account for all the
other adaptations for perception, cognition, and movement, and all the other important domains
of behavior such as foraging, parenting, making friends, trading goods and services, and
avoiding predators and parasites. The theory does not apply to all the psychological adaptations
that we share with other vertebrates, mammals, primates, and apes. It does not address the
quandary of 'consciousness' or the dynamics of cultural change, though it might have some
bearing on these issues. It is best at explaining behaviors that young adults display more than
children or older people do, that men display more conspicuously than women do, that highfitness people display more than low-fitness people, that take lots of energy, time, and skill, that
reveal genetic quality, and that people cite as sexually desirable traits. I leave it to others to
discuss the existential and theological implications of living in a lineage that directed its own
evolution through its powers of mate choice.
58. One weakness of any theory that relies on sexual selection is that sexual selection theory
(like natural selection theory) is still very much under development, with debates continuing
about the heritability of fitness, the relative importance of indexes versus handicaps, the
dynamics of sexual selection given diverse preferences and multiple ornaments, and the gametheoretic complexities of mating markets given mutual mate choice. As the higher-level metatheory of sexual selection develops, some of my mid-level hypotheses about human mental
evolution may turn out to be evolutionarily implausible. Given the minimal sex differences in
most human courtship abilities discussed in the book, a high priority should be given to the
development of better models of sexual selection under mutual mate choice.
59. Another weakness concerns traits like language, that probably evolved through some
interplay of sexual selection and other forms of social selection (including group selection
between different evolutionary equilibria). Arguably, the theory over-emphasizes the courtship
functions of language and creative intelligence, while neglecting their other fitness benefits in
teaching children, making friends, helping kin, trading services, making commitments,
sustaining social norms, fighting other tribes, and so forth. However, my intention was not to
dismiss these other benefits, only to stress a sexual-attraction benefit that had been neglected
in previous theorizing.
60. A third weakness is the provisional nature of the reconstruction of hominid mating patterns.
This reconstruction is based on current data from archaeology, anthropology, psychology,
primatology, and genetics. However, today's data may be supplanted by tomorrow's. Given the
number of radical re-thinks that have occurred about prehistory over the last several decades, it
would be foolish to pretend that the current reconstruction of Pleistocene mating is the last word
on the subject. Nevertheless, the requirements for sexual selection to influence the mind's
evolution would remain valid under a fairly wide range of mating patterns, because only
perfectly random mating would render mate choice irrelevant.
61. The book also has some pseudo-weaknesses that aren't really specific to this theory.
Evolutionary accounts of the most cherished human abilities are often criticized as 'genetic
determinism' by those who wish to retain the mystique of the humanities and the performing
arts. Such criticisms are generic to all adaptationist accounts of human creativity, and are
especially inappropriate to this sexual selection account, which emphasizes the feedback loop
between psychology and biology via mate choice, and sexual selection's ability to favor nondeterministic, unpredictable, creative forms of courtship.
62. Another pseudo-weakness is that the theory only has patchy evidence in its support at
present. Any evolutionary theory that relies on existing data can be dismissed as a 'Just-so
story' that just offers post-hoc interpretations of known facts; whereas any that sticks its neck
out and makes novel predictions not yet supported by evidence can be dismissed as
'speculative'. Obviously, the best theories must rely on some evidence and make some
predictions, so may appear both post-hoc and speculative. That quandary is generic to all
scientific theories, from physics through psychology. The real issue is testability (a broader,
more realistic, Lakatosian version of Popper's falsifiability criterion), and fortunately, the last two
decades of biological research on animal mate choice have produced ever-better
methodologies for testing hypotheses about sexual selection, which can also be applied to
humans. Likewise for genetic and neuroscientific evidence supporting the existence of these
courtship adaptations: most senior scientists with power to allocate time on the relevant lab
equipment won't bother looking for such evidence until someone points out the possible
scientific benefits of doing so.
63. Much more empirical research is needed on mate choice for mental traits among humans
across diverse cultures, ranging from tribal hunter-gatherers to affluent Westerners. We need
more behavior- genetic work on the inheritance of mate preferences and courtship abilities, and
the heritability of variance in those adaptations. We need more developmental psychology work
on the emergence of these adaptations over the life-course, and their facultative sensitivity to
changes in personal mate value, mating markets, and parental responsibilities. The hypothesis
that there is a general fitness factor (superordinate to both the g factor and general physical
health) needs to be tested with large, representative datasets that include psychometric,
anthropometric, health, social status, and other diverse measures of fitness-relevant traits. More
data is needed on the metabolic costs (e.g. glucose burn rates) of different mental activities, to
see whether courtship draws disproportionately on the costliest. Cognitive neuroscience could
try to localize courtship adaptations in the brain. Most importantly, we need much better
observations concerning real-life human courtship, including the measurable aspects of
courtship that influence mate choice, the reproductive (or at least sexual) consequences of
individual variation in those aspects, and the social-cognitive and emotional mechanisms of
falling in love.
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