adaptation A biological trait that evolved through natural selection or sexual selection to promote survival or reproduction in a particular way.
adaptive radiation The branching out of a number of species from a common ancestor, as a result of that ancestor having evolved a useful new adaptation that allows it to spread into new ecological niches.
altruism Helping others without direct benefit to oneself. Apparent altruism can evolve only through indirect or hidden benefits to one’s genes.
anthropology The study of human evolution (physical anthropology) and human cultures (cultural anthropology).
archaic Homo sapiens Ancestral hominids that lived in Africa, Europe, and Asia from about 400,000 to about 100,000 years ago, fairly similar to modern humans, with large brains.
archeology The study of prehistoric artifacts and human remains.
artificial selection The selective breeding and domestication by humans of other species, e.g. breeding dairy cattle for maximum milk yield.
assortative mating Sexual choice for traits similar to one’s own, e.g. tall women favoring tall men.
Australopithecine One of a set of hominids that lived about 4 to 1 million years ago; bipedal, with strong jaws and small, ape-sized brains. The earlier ones were probably ancestral to humans.
band A social group of hunter-gatherers, usually around 20 in number, occupying a local territory.
behavior genetics The study of the inheritance of human and animal behavior, often using twin and adoption studies (to separate genetic from environmental effects) and molecular genetics methods to identify specific genes.
behaviorism A school of psychology, flourishing from about 1920 to 1970, that tried to explain behavior through learned associations between stimuli and responses, without reference to minds, intentions, behavior genetics, or evolutionary functions.
bonobo A species of great ape previously known as the “pygmy chimpanzee.” Very sexual and very clever, bonobos are found in Zaire and are closely related to the common chimpanzee.
bowerbird One of the 18-odd species of birds in New Guinea and Australia in which males attract females by building ornamental nests called bowers.
brain size A convenient indicator of the number and complexity of psychological adaptations that have evolved in a species. Brain size can be estimated from fossil skulls, and correlates 40 percent with intelligence in modern humans.
cognitive psychology An area of psychology that studies the mental processes that underlie perception, categorization, judgment, decision-making, memory, learning, and language.
cognitive science The interdisciplinary study of intelligence based on the computer metaphor for the mind, excluding research on individual differences in intelligence, its heritability, or its evolution.
condition-dependence A trait’s sensitivity to an animal’s health and energy level. For example, dance ability is condition-dependent because tired, sick animals can’t dance very well.
consortship Exclusive association between a male and a female in estrus, during which the male tries to keep the female sexually separated from other males.
conspicuous consumption Costly indicators of wealth displayed to achieve social status—the human cultural analog of sexually selected handicaps.
convergent evolution The independent evolution in separate lineages of adaptations that serve the same function.
copulatory courtship Energetic, prolonged copulation that provides mutual evidence of fitness through mutual pleasure.
courtship effort The time, energy, skill, and resources spent trying to impress potential sexual partners.
Darwinian aesthetics The evolutionary analysis of what people find beautiful, by viewing human aesthetic preferences as adaptations for favoring habitats, foods, tools, and sexual partners that promote one’s reproductive success.
death A misfortune that precludes further courtship or reproduction.
developmental stability An organism’s ability to grow a complex body part in its normal form, despite various environmental and genetic stresses. For body parts that are normally symmetrical, symmetry is an indicator of developmental stability.
dimorphism bodily differences between males and females.
discriminative parental solicitude The tendency of parents to direct their care and attention to offspring that are more likely to survive and reproduce.
display A conspicuous behavior shaped by evolution to advertise fitness, condition, motivation, or desperation.
dominance The ability to intimidate other individuals into giving up food, territory, or sexual partners.
ecological niche The position of a species within an ecology, including its habitat, food supply, and relations to predators and parasites.
equilibrium In game theory, any situation in which no player can do better by changing their strategy, given what other players are already doing.
equilibrium selection Any process that leads a population to play one equilibrium rather than another in a strategic game that has more than one possible equilibrium. It can occur through genetic evolution, cultural history, or individual learning.
estrus Signs of ovulation manifest in a female’s body or behavior, evolved to attract males and incite male–male competition.
ethology The study of the mechanisms and functions of animal behavior in the wild.
evolution Descent with cumulative genetic modification, due to natural selection, sexual selection, and various random effects.
evolutionary psychology The study of human psychological adaptations, including their evolutionary origins, adaptive functions, brain mechanisms, genetic inheritance, and social effects.
extended phenotype An organism considered as a set of adaptive effects that reach out into the environment to promote its survival and reproduction. It can include evolved traits like beaver dams, spider webs, bowerbird bowers, and hominid handaxes.
female The sex that produces larger gametes called eggs.
fitness (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.
fitness indicator An adaptation that evolved to advertise an individual’s fitness during courtship and mating, typically by growing an ornament or performing a behavior that a lower-fitness individual would find too costly to produce.
fitness matching 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.
foraging Finding wild plant and animal foods to eat.
function How an adaptation evolved to promote survival or reproduction under ancestral conditions.
g factor The basic dimension of general intelligence and brain efficiency that accounts for the positive correlations between scores on mental tests. Basically, it is what IQ tests try to measure.
game theory The study of interdependent decision-making in situations where each player’s payoffs depend on how their own strategies interact with the strategies of other players. Game theory is studied mostly by economists.
gamete A reproductive cell such as a sperm or egg.
gene A piece of DNA long enough to code for some biological information but short enough to survive many generations of sexual recombination. The gene is the basic unit of replication and selection in evolution.
gene–culture co-evolution The hypothesis that the human brain enlarged to learn more culture, which allowed cultures to become more complex, which in turn selected for larger brains, and so forth.
gene pool The total set of genes in a population.
genetic algorithm A computer program that evolves solutions to specified problems by applying selection, mutation, and genetic recombination to populations of simulated individuals that represent possible solutions.
genome The complete set of genetic information in an organism. The human genome contains over 60,000 genes and 3 billion DNA base pairs.
group selection Competition between groups that favors group-benefiting adaptations such as altruism or equilibria with high mutual payoffs.
handaxe A stone artifact with a roughly triangular outline, two symmetric faces, and a sharp edge around the circumference Handaxes were made from about 1.6 million years ago until 50,000 years ago by various hominids.
handicap A costly, reliable indicator of fitness, often a result of sexual selection.
handicap principle The idea that fitness indicators can be reliable only if they impose such costs that low-fitness pretenders cannot afford them.
heritability For traits that vary between individuals, the proportion of that variation that is explained by genetic differences between the individuals. Heritability can range from 0 to 100 percent.
Holocene The geological era from 10,000 years ago to the present.
hominid Any of the bipedal apes of the last few million years, whether our direct ancestors or not.
Homo erectus A medium-brained hominid that flourished from about 1.8 million years ago to about 400,000 years ago (in Africa) and 50,000 years ago (in parts of east Asia).
human nature The complete set of psychological adaptations that has evolved in our species.
hunter-gatherers Humans or proto-humans living in small bands without farming or animal herding. Females typically raise the children and gather water, firewood, fruits, tubers, vegetables, berries, and nuts. Males sexually compete by playing status games such as warfare, hunting, and pretending to have spiritual powers. Before 10,000 years ago all humans were hunter-gatherers.
ideology A system of beliefs that has become sufficiently popular in a culture that believers stand a decent chance of finding a like-minded mate.
indicator A trait that evolved to advertise a particular aspect of an individual’s fitness, condition, or motivation.
intelligence Mental fitness, as measurable by intelligence tests and displayed in verbal courtship. In this book, intelligence means the highly heritable “g factor” that underlies individual differences in a vast array of behavioral and cognitive abilities.
kin selection An evolutionary process that tends to favor generosity to blood relatives, in proportion to their genetic relatedness.
lek A place where males congregate to attract females with songs, dances, and visual ornaments.
lineage A line of common descent; a succession of organisms linked by genetic inheritance.
love An emotional adaptation for focusing courtship effort on a particular individual.
Machiavellian intelligence theory The idea that the large brains and high social intelligence of apes and humans evolved to deceive and manipulate others within a social group.
male The sex that produces smaller gametes called sperm.
marketing Designing, producing, advertising, delivering, pricing, and selling products that satisfy consumer preferences: the economic analog of sexual selection through mate choice.
marriage A socially legitimated sexual relationship in which sexual fidelity and parental responsibilities are maintained through the threat of social punishment.
mate choice Choice of sexual partners. This book prefers “sexual choice,” which is less confusing for Anglo-Australian cultures, in which a “mate” is a non-sexual friend who reciprocates beer-buying behavior.
meme A unit of cultural information transmitted by imitation.
mixed strategy A strategy that randomizes behaviors in a certain proportion to keep an opponent guessing about a player’s next move.
Modern Synthesis The integration of Darwinian evolutionary theory and Mendelian genetics that was achieved in the 1930s.
monogamy An exclusive sexual relationship of one male with one female.
morphology The physical structure of an organism; its body form.
mutation A spontaneous change in the structure or sequence of a DNA strand that changes how a gene works. Usually a bad idea.
mutation–selection balance An evolutionary equilibrium in which selection removes harmful mutations at the same average rate that harmful mutations arise.
mutual choice When both sexes are choosy about their sexual partners.
natural selection Changes in the gene pool of a species due to differences in the ability of individuals to survive and reproduce. Against current biological fashion, this book follows Darwin in using “natural selection” to cover differences in survival ability only, and “sexual selection” to cover differences in reproduction ability.
Neanderthal A species of hominid that flourished in Europe and western Asia from about 300,000 years ago until 50,000 years ago. Stocky, large-nosed, and large-brained, they were apparently not our direct ancestors.
neoteny The persistence of juvenile traits into adulthood, including bulbous heads, small jaws, and playful gregariousness.
ornament (1) In biology, a trait that evolved through sexual choice to appear sexually attractive. (2) In aesthetics, a hard-to-fake display of artistic skill and time, viewed as wasteful decadence by the Bauhaus and other 20th century modernist movements.
ornamental mind theory The idea that the human mind evolved through sexual choice as a set of entertainment systems used in courtship.
parasite load The number of parasites carried by an organism. High parasite loads impair condition, reducing health and sexual attractiveness.
parental investment Any care, protection, or effort given by parents that increases offspring fitness at a cost to the parent.
phenotype The observable traits of an organism, including body and behavior.
Pleistocene The geological epoch that began 1.64 million years ago and ended 10,000 years ago, during which almost all of human evolution happened.
polyandry (“many men”) A sexual relationship in which one female copulates regularly with more than one male partner. Sometimes observed in Tibet.
polygamy (“many marriages”) A legal system in which an individual can legitimately marry more than one spouse.
polygyny (“many women”) A sexual relationship in which one male copulates regularly with more than one female partner, found in most human cultures throughout history.
population A group of individuals that tend to mate with each other.
population genetics The area of biology that models how evolution changes gene frequencies in populations.
primatology The scientific study of the 300-odd species of primates, including apes, monkeys, lemurs, lorises, tarsiers, marmosets, and tamarins.
promiscuity Mating by a female with many males to maximize sperm competition within her reproductive tract; favored by chimpanzees.
protean behavior Adaptively unpredictable behavior, as when prey zigzag randomly to escape from predators. Named for the mythical Greek shape-shifter Proteus.
psychological adaptation An inherited behavioral capacity that evolved to promote survival or reproduction in a particular way under ancestral conditions.
reciprocal altruism The theory that mutual generosity can evolve if individuals take turns giving and receiving benefits across many encounters.
reportability The ability to talk about one’s subjective experiences.
reproductive success The number of viable offspring produced by an individual. Reproductive success is the basic currency of evolutionary success.
ritualization Evolutionary modification of a behavior for greater effectiveness as a display, through standardization, repetition, and amplification.
runaway brain theory The idea that the human brain evolved through runaway sexual selection.
runaway sexual selection A positive-feedback process that amplifies the size and complexity of sexual ornaments.
savanna Open grassland with scattered shrubs and trees, and alternating dry and wet seasons (rather than winters and summers), typical of East Africa where humans evolved.
Scheherazade strategy Keeping a sexual partner interested in oneself by telling good stories and being a good conversationalist.
selection pressure Any feature of the physical, biological,
social, or sexual environment that causes some individuals to survive or reproduce better than others.
selfish gene A gene that acts as if it is trying to replicate itself; the gene considered as the unit of evolutionary selection.
sensory bias theory The idea that animal senses are more responsive to some stimuli than others, and that this can influence sexual selection to produce ornaments with sensory appeal.
serial monogamy A mating strategy in which individuals go through a series of monogamous sexual relationships (lasting a few weeks to several years) over the course of their lives. Serial monogamy has probably been the norm in human evolution.
sexual choice Choice of some sexual partners in preference to others. It has been a driving force behind sexual selection and evolution.
sexual preferences The criteria for sexual choice, whether perceptual, cognitive, emotional, or social.
sexual reproduction The production of offspring by combining an egg from a mother with sperm from a father; the prerequisite for sexual selection.
sexual selection Evolutionary change due to heritable differences in the ability to attract sexual partners, repel sexual rivals, or do anything else that promotes reproduction.
signal Any behavior that evolved to convey information from one animal (the signaler) to another (the receiver). Most signals convey information about a signaler’s fitness, condition, motivation, or location.
social selection Selection for the ability to promote one’s survival and reproduction by attaining social status and managing social relationships, including sexual relationships.
sociolinguistics The study of the social variations and uses of human language, especially as a function of age, sex, class, and ethnicity.
speciation The splitting apart of one population to form two species that no longer interbreed with each other.
species A group of organisms willing to breed with one another. The species is the basic unit of biological classification.
sperm competition Competition between sperm to fertilize an egg, which occurs when a female has mated with two or more males.
status Socially recognized merit, often used as a fitness indicator in sexual choice.
strategic handicap A costly behavioral display, such as dance or speech, that can easily be turned off if an animal is in poor condition. A strategic handicap is very efficient as a fitness indicator.
survival of the fittest A catchy but misleading phrase invented by Herbert Spencer to describe natural selection, which led biologists to neglect sexual selection.
Theory of Mind The ability to attribute beliefs and desires to other individuals, in order to better understand their behavior. The theory of mind is a key component of Machiavellian intelligence theory.
tribe A small society with a distinctive language and culture, typically a cluster of kin groups that interbreed.
universal Typical of all normal humans across cultures and history, suggesting an evolutionary rather than a cultural origin.
verbal courtship Talking to attract a sexual partner.
virtues Behavioral abilities and motivations that are socially approved and sexually desired.
waste The apparently pointless costs (in time, energy, resources, and risk) of sexual display that keep the displays reliable as indicators of fitness (in biology) or wealth (in modern culture).