evolutionary psychology

n. Evolutionary psychologists propose that the human mind consists predominantly of highly specialized mechanisms designed to solve specific problems. The specific problems that the human mind is designed to solve are those that repeatedly confronted our ancestors over evolutionary time.

The ancestral environment that humans evolved in is termed the environment of evolutionary adaptedness (EEA). This environment consists of a set of problems that must be solved if the animal is to avoid extinction. For example, over evolutionary time, humans and their primate ancestors had to be able find mates and raise children, and they had to form alliances with others. They had to be able to find food, and they had to avoid dangerous predators and poisonous plants and animals. The problems that humans faced during their evolution were quite different from the problems faced by other living organisms. For example, an ocean-dwelling mammal such as a whale must solve a wide range of problems stemming from its need to adapt to living in the ocean, and parasites must often adapt to the internal environment of a variety of hosts.

For humans, the EEA is considered to be the Pleistocene geological era, which spanned a period from 1.8 million years ago to 12,000 years ago. During this period, humans lived as hunter-gatherers, so it is expected that human psychological adaptations are adapted to life during this period. Because human culture has changed so dramatically, there may be mismatches between psychological adaptations and the modern world. An example is that food was relatively scarce and unpredictable in the EEA compared to the modern world of readily available high- calorie, high-fat food. The result is that modern humans are prone to obesity because our psychological mechanisms are geared to an environment of scarcity that no longer obtains in many parts of the world.

Evolutionary psychologists emphasize that all of these problems presented themselves repeatedly over evolutionary time so that there would be sufficient opportunity for natural selection to design mechanisms that would solve the problems. According to evolutionary psychology, these problems were solved by evolving a set of specialized psychological mechanisms designed to deal with these specific problems. These mechanisms are adaptations - mechanisms designed by natural selection to solve a particular problem. For example, on the basis of a large body of theory and data, evolutionary psychologists argue that humans evolved mechanisms that allow them to choose mates in an adaptive manner: women are attracted to men willing and able to invest in their children, and men are attracted to youthful, physically attractive women because these traits are signs of fertility.

When the environment presents longstanding problems and recurrent cues relevant to solving them, the best solution is to evolve domain-specific mechanisms, or modules, specialized to handle specific inputs and generate particular solutions. Modules are designed to solve problems in specific domains by mapping characteristic inputs onto characteristic outputs. For example, the human visual system contains specialized cells that are designed to respond to particular types of sensory input (horizontal lines, vertical lines, motion), and there are specific pathways in the brain that are specialized to transmit visual information. These pathways are specific to the visual system and are unresponsive to other stimulation, such as sound. Modules are therefore domain specific. That is, each module processes information peculiar to its own area of "expertise," so that, for example, verbal and spatial information are processed with different mechanisms.

The operation of modules is mandatory (i.e., they are automatically triggered in the presence of appropriate environmental stimulation), fast, and unconscious. For example, when we look around the room, our brains are automatically carrying out millions of operations that allow us to see the objects in the room. The calculations are done very rapidly, and we are unaware of them. Modules operate in parallel, processing massive amounts of information in a variety of relatively independent circuits at the same time. For example, when we converse with people in garden-variety social contexts, we unconsciously process their facial expressions, age- and gender-related cues, vocal intonation, posture, psychological traits, and language.

Research in evolutionary psychology has been influenced by several theories compatible with general evolutionary theory. The most important of these theories are parental investment theory, inclusive fitness theory, parent-offspring conflict theory, and the theory of senescence.

Inclusive fitness theory emphasizes that genes are selected for their beneficial effects not only on the reproductive success of individuals but also on their relatives. This occurs because relatives share genes depending on how closely related they are (e.g., full siblings share half of their segregating genes). This theory predicts that psychological mechanisms sensitive to kinship will favor helping relatives over nonrelatives and more closely related kin over more distantly related kin.

Parent-offspring conflict theory is based on the hypothesis that differing degrees of genetic relatedness within families produce conflicts of interest. For example, parents and children are expected to differ on the ideal amount of investment parents provide children: parents share half of their segregating genes with each of their children, but it is in each child's interest to favor itself over its siblings. This theory predicts that parents will encourage children to be more cooperative than is in the children’s interest. And it predicts conflicts of interest over time of weaning, with parents more inclined to invest in new children and children seeking more investment in themselves.

Senescence theory proposes that genes that promote reproductive success early in life will be retained even if they shorten the life span. This follows from the fact that offspring produced relatively early in life have a greater effect on an individual's reproductive success than offspring produced later in life. These effects are especially pronounced in males because sexual competition is expected to be higher for males than females. Senescence theory therefore predicts that males will have shorter life spans than females on average.

Although mapping modular mechanisms and exploring the predictions resulting from evolutionary theory characterize the great bulk of research in evolutionary psychology, there has been increasing interest in the evolution and function of domain general mechanisms, especially among evolutionary psychologists interested in human development. An important set of domain general mechanisms comprises general intelligence, particularly working memory and attentional control. Unlike the unconscious workings of the modular mechanisms described earlier, general intelligence involves explicitly conscious, effortful problem solving. Whereas the modules are relatively independent processors operating in parallel, the explicit mechanisms of general intelligence operate on very limited bits of information in a sequential manner. And whereas the modules are domain specific, general intelligence is domain general: it operates on a wide range of input, including verbal and spatial information.

Because general intelligence is fundamentally concerned with coping with environmental novelty, there are three types of hypotheses regarding the main factor driving the increase in human intelligence: climatic variation, ecological pressure, and social competition. The climatic variation hypothesis proposes that human intelligence was mainly beneficial in decoupling humans from dependence on any particular ecology defined by a constant climate or other invariant features. According to this hypothesis, general intelligence allowed humans to adapt to rapidly changing climates of the Pleistocene and greatly increased their range of settlement. The foraging hypothesis highlights the advantages to be gained from better methods for extracting resources from the environment (e.g., managed foraging) and in enlarging the range of human settlement and supporting larger populations. The foraging hypothesis is supported by data indicating that humans evolved as superpredators and manufacturers of highly complex tools by around 50,000 years ago, resulting in a wave of mass extinctions of large animals. These changes coincide with not only a larger brain but a smaller gastrointestinal tract and higher metabolism dependent on high-quality food made possible by these improved foraging techniques. The social competition hypothesis proposes that after humans achieved ecological dominance, intelligence evolved because it was beneficial for between-group and within-group competition among humans. This hypothesis emphasizes that cognitively, socially, and behaviorally sophisticated individuals are able to outmaneuver and manipulate other individuals to gain control of resources in the local ecology and to gain control of the behavior of other people. This hypothesis is supported by correlations between brain size and group size, especially where there are complex social relationships within groups.

-KM

► See also PARENTAL INVESTMENT THEORY