Early theories of culture tended to reject the importance of biology in explaining cultural phenomena. Instead culture was seen as a superorganism unaffected by human nature. In contrast to the view of the cultural relativists, Donald Brown argued that there are many cultural universals, and some of these might be the product of a comparatively fixed underlying human nature. Tooby and Cosmides propose that evoked culture might give rise to contingent universals, practices that are the result of mental models being sensitive to certain environmental conditions. Many evolutionists argue that many cultural practices are constrained by genes; culture exists to improve our inclusive fitness. Richerson and Boyd are more concerned with how our ability to acquire and learn culture evolved, what factors led to the ‘cultural revolution’. They argue that culture provides us with a second mode of inheritance that evolved as a way of adapting to an environment.

The cognitive approach sees behaviour as resulting from the operation of internal mental processes. Our visual systems did not evolve to present us with a true description of the world; rather, they evolved to give us a useful description of the world that supports our actions upon it. We can see this in perceptual constancies in which a changing world is stabilized by the actions of our visual system, resulting in visual illusions. Although problems such as under-age drinking are often thought of as problems of logic (such as the abstract Wason task), they are perhaps better thought of as problems of duties and obligation and play a role in detecting freeriders to better enable cooperation. Statistical misconceptions such as the gambler’s fallacy and the hot hand fallacy may arise from our sensitivity to the patchiness of the world that we inhabit.

Evolutionary psychopathology is concerned with understanding physical and mental health-related disorders through evolutionary principles. The symptoms caused by microbial parasites such as viruses, bacteria, fungi and protozoa can be viewed as adaptations either of the pathogen to aid its multiplication or of the host in order to kill off or expel it. Evolutionary explanations for current-day physical and mental symptoms include the notion that our bodies and minds are adapted to the pressures of a stone-age existence but are living under modern-day conditions – the mismatch or time lag argument. Other explanations include the idea that genes which cause illness might also have positive facets associated with them – the pleiotropy argument; that selection pressures act on increasing inclusive fitness, not on perfecting systems – the compromise argument; and that disorders might be viewed as the extremes of normal variation – the trait variation argument.

By the mid-nineteenth century many scientists considered the notion of evolution seriously but the mechanism for this was lacking. In 1859 Charles Darwin introduced just such a mechanism – natural selection which is based on heritable variation and differential reproductive success. Hence individuals with characteristics which allow them to survive and outbreed others pass on such characteristics to future generations. The work of Williams, Hamilton and Trivers led evolutionists to reconsider the level at which selection operates. In The Selfish GeneRichard Dawkins made explicit the notion of the gene as the unit of selection and introduced the concepts of the replicator and the vehicle. The replicator is the gene and the vehicle the organism. Debates concerning individual versus gene selection continue. Generally, selection pressures which act on individuals will also act on genes directly. In the case of altruistic behaviour, however, this may not always be the case.

Comparisons with chimps, bonobos and gorillas reveal a number of substantial differences between apes and humans. Humans eat far more meat than primates, and, due to a lack of an oestrous swelling, a woman’s oestrus cycle is a mystery to men. Human infants require high parental investment. Neonate survival benefits from the lengthy pair bond that humans generally form. For long-term relationships both men and women look for loving and dependable partners who are in good health. Where the sexes differ lies in men’s greater emphasis on good looks and women’s preference for status and wealth. The reproductive strategy of an individual will depend on a number of factors such as the availability of suitable partners and the perceived attractiveness and age of a person. Evolutionary psychologists suggest that a woman’s mating strategy may be influenced by the nature of her parents’ relationship during her childhood.

In 1872 Darwin published The Expression of the Emotions in Man and Animalswhere he argued that there are a number of emotional expressions which are innate and common to all cultures – universal emotions. Such expressions include sadness, anger, surprise and enjoyment. The universality of human emotions is supported by three forms of evidence. Comparison with other primates suggests a common evolutionary ancestor; cross-cultural studies suggest that different cultures recognize and experience the same basic emotions; and certain areas of the human forebrain appear to be particularly associated with emotional states. Specifically, the amygdala and the orbitofrontal cortex. Negative states such as fear and anger may have evolved in order to place people in the correct psychological and physiological state to deal with aversive circumstances. Positive emotions such as love might serve the function of placing us in the appropriate psychological state to help build up social relationships.

Individual differences researchers investigate many kinds of psychological variation, but the most widely studied of these are personality and intelligence. Personality is defined in many ways, but one way of thinking of it is as a form of motivational system which predisposes people to seek out particular situations and respond in particular ways. Personality is measured most frequently by self-report questionnaires. These questionnaires usually describe a personality on a number of dimensions of factors (e.g. extraversion, neuroticism, psychoticism). Research using twin studies suggests that personality is moderately heritable. Theories developed to explain variation in personality have to account for both heritable and non-heritable components. It is necessary not only to understand why personality might be passed on through the genes, but also why so much of the variation in personality appears to be due to the environment. Various theories were advanced to explain both of these aspects of personality.

In 1871 in The Descent of Man and Selection in Relation to Sex, Darwin introduced the notion of sexual selection. Sexual selection leads to features that help individuals gain access to mates and takes two forms – intrasexual and intersexual selection. Intrasexual selection involves competition between members of one sex for access to the opposite sex, while intersexual selection involves members of one sex attempting to attract members of the opposite sex. In nature these forces are believed to lead to elevated levels of aggression, greater body strength and the development of attractive features in males. For females sexual selection leads to choosiness over mates. Sexual selection theory and the notion of female choice have recently become important concepts for the understanding of behaviour. There is now clear evidence from a number of species that female choice has been a driving force in the evolution of male adornment and aggressive behaviour.

Evolutionary psychologists used the concepts of inclusive fitness theory, evolved psychological mechanisms and kin altruism to help explain social behaviour in ourselves and animals. Inclusive fitness is an estimate of the number of genes that individuals pass on both directly via their offspring and indirectly via their effects on the survival of other kin. Kin altruism is the term used for self-sacrificing acts towards kin. The tendency to provide aid to relatives appears to be related to the proportion of genes shared by common descent (the coefficient of relatedness). Evolutionists explain many acts of social behaviour in animals in terms of nepotistic strategies. Parental investment consists of the amount of time and effort that an individual puts into rearing each of its offspring. The grandmother hypothesis is the notion that the menopause came about because, by shifting their investment from offspring to grandoffspring, a woman can increase her inclusive fitness.

Evolutionary psychology attempts to provide ultimate as well as proximate explanations of human behaviour. Proximate mechanisms are those that directly cause a particular behaviour (for instance we have sex because we enjoy it), whereas ultimate explanations are cast at the level of design by natural selection (we have sex because it leads to offspring). The concept of evolution is an old one. What was missing from these earlier accounts was a workable model of how change occurs. Darwin provided this mechanism with his theory of natural selection. Much of twentieth-century psychology has been influenced by the cultural relativist position and the biological bases of human behaviour have tended to be ignored or downplayed. The sociobiology movement attempted to formulate evolutionary explanations of human behaviour. Such attempts led to a great deal of scientific and political controversy that continues to this day.

A life history theory of development claims that, from an early age, children monitor their environment and make decisions about their future reproductive value. Based on their assessment of environmental conditions, they can choose to maximize current or future reproductive success. Attachment theory claims that early attachments can have a substantial effect on subsequent personality and behaviour. Central to this theory is that a child forms a ‘working model’ of the self and relationships that is used to guide subsequent behaviour. Secure working models generally lead to more satisfactory and stable relationships in later life than insecure ones. Ainsworth proposed that there are three attachment styles, secure, insecure-avoidant and insecure-anxious/resistant. Evidence suggests individuals exhibiting insecure attachment styles generally suffer more relationship problems later in life. Unlike chimpanzees, which prefer to act alone unless it is impossible to do so (such as a hunt), children prefer to cooperate with others.