Imagine writing a story about the people you know. To capture their special qualities, you might describe their traits: Keesha is friendly, aggressive, and domineering; Seth is flaky, humorous, and superficial. The trait approach to personality uses such trait terms to characterize differences among individuals. In attempting to create manageable and meaningful sets of descriptors, trait theorists face two significant challenges: narrowing down the almost infinite set of adjectives and answering the more basic question of why people have particular traits and whether they arise from biological or hereditary foundations.

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One way to think about personality is as a combination of traits. This was the approach of Gordon Allport (1937), one of the first trait theorists, who believed people could be described in terms of traits just as an object could be described in terms of its properties. He saw a trait as a relatively stable disposition to behave in a particular and consistent way. For example, a person who keeps his books organized alphabetically in bookshelves, hangs his clothing neatly in the closet, and keeps a clear agenda in a daily planner can be said to have the trait of orderliness. This trait consistently manifests itself in a variety of settings.

The orderliness trait describes a person but doesn’t explain his or her behavior. Why does the person behave in this way? There are two basic ways in which a trait might serve as an explanation: The trait may be a preexisting disposition of the person that causes the person’s behavior, or it may be a motivation that guides the person’s behavior. Allport saw traits as preexisting dispositions, causes of behavior that reliably trigger the behavior. The person’s orderliness, for example, is an inner property of the person that will cause the person to straighten things up and be tidy in a wide array of situations. Other personality theorists suggested instead that traits reflect motives. Just as a hunger motive might explain someone’s many trips to the snack bar, a need for orderliness might explain the neat closet and alphabetically organized bookshelves (Murray & Kluckhohn, 1953). Researchers examining traits as causes have used personality inventories to measure them, whereas those examining traits as motives have more often used projective tests.

Picking a single trait such as orderliness and studying it in depth doesn’t get us very far in the search for the core of human character: the basic set of traits that defines how humans differ from one another. How have researchers tried to discover the core personality traits?

Classification Using language

The study of core traits began with an exploration of how personality is represented in the store of wisdom we call language. Generation after generation, people have described people with words, so early psychologists proposed that core traits could be discerned by finding the main themes in all the adjectives used to describe personality. In one such analysis, a painstaking count of relevant words in a dictionary of English resulted in a list of over 18,000 potential traits (Allport & Odbert, 1936)! Attempts to narrow down the list to a more manageable set depend on the idea that traits might be related in a hierarchical pattern (see FIGURE 11.3), with more general or abstract traits at higher levels than more specific or concrete traits. The highest-level traits are sometimes called dimensions or factors of personality.

But how many factors are there? Different researchers have proposed different answers. Cattell (1950) proposed a 16-factor theory of personality (way down from 18,000, but still a lot), whereas Hans Eysenck (1967) simplified things nicely with a model of personality with only two major traits (although he later expanded it to three). Eysenck identified one dimension, Extraversion, that distinguished people who are sociable and active (extraverts) from those who are more introspective and quiet (introverts). He also identified a second dimension, Neuroticism, ranging from the tendency to be very neurotic or emotionally unstable to the tendency to be more emotionally stable. The third factor he proposed was Psychoticism, which refers to the extent to which a person is impulsive or hostile. (Notably, the term “psychotic” nowadays refers to an abnormal mental state marked by detachment from reality. This is discussed further in the Disorders chapter.)

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The Big Five Dimensions of Personality

Today, most researchers agree that personality is best captured by 5 factors rather than by 2, 3, 16, or 18,000 (John & Srivastava, 1999; McCrae & Costa, 1999). The Big Five, as they are affectionately called, are the traits of the five-factor personality model: openness to experience, conscientiousness, extraversion, agreeableness, and neuroticism (see TABLE 11.1; remember them by the initials O.C.E.A.N.). The five-factor model, which overlaps with the pioneering work of Cattell and Eysenck, is now widely preferred for several reasons. First, this set of five factors strikes the right balance between accounting for as much variation in personality as possible while avoiding overlapping traits. Second, in a large number of studies using different kinds of data (people’s descriptions of their own personalities, other people’s descriptions of their personalities, interviewer checklists, and behavioral observation), the same five factors have emerged. Third, and perhaps most important, the basic five-factor structure seems to show up across a wide range of participants, including children, adults in other cultures, and even among those who use other languages, suggesting that the Big Five may be universal (John & Srivastava, 1999). It turns out that the Big Five personality traits also predict people’s online behavior on social networking sites such as Facebook (see the Hot Science box).

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Interestingly, research on the Big Five has shown that people’s personalities tend to remain fairly stable through a lifetime: Scores at one time in life correlate strongly with scores at later dates, even decades later (Caspi, Roberts, & Shiner, 2005). William James offered the opinion that “in most of us, by the age of thirty, the character has set like plaster, and will never soften again” (James, 1890, p. 121), but this turns out to be too strong a view. Some variability is typical in childhood, and though there is less in adolescence, some personality change can even occur in adulthood for some people (Srivistava et al., 2003).

Can we explain why a person has a stable set of personality traits? Many trait theorists have argued that unchangeable brain and biological processes produce the remarkable stability of traits over the life span. Brain damage certainly can produce personality change, as the classic case of Phineas Gage so vividly demonstrates (see the Neuroscience and Behavior chapter). You may recall that after the blasting accident that blew an iron rod through his frontal lobes, Gage showed a dramatic loss of social appropriateness and conscientiousness (Damasio, 1994). In fact, when someone experiences a profound change in personality, testing often reveals the presence of such brain pathologies as Alzheimer’s disease, stroke, or brain tumor (Feinberg, 2001). The administration of antidepressant medication and other pharmaceutical treatments that change brain chemistry also can trigger personality changes, making people, for example, somewhat more extraverted and less neurotic (Bagby et al., 1999; Knutson et al., 1998).

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Genes, Traits, and Personality

Some of the most compelling evidence for the importance of biological factors in personality comes from the domain of behavioral genetics. Simply put, the more genes you have in common with someone, the more similar your personalities are likely to be. For example, in one review of studies involving over 24,000 twin pairs (Loehlin, 1992), identical twins (who share 100% of their genes) proved markedly more similar to each other in personality than did fraternal twins (who share on average only 50% of their genes). And identical twins reared apart in adoptive families end up at least as similar in personality as those who grew up together (McGue & Bouchard, 1998; Tellegen et al., 1988). These and other studies suggest that simply growing up in the same family does not make people very similar. Rather, when two siblings are similar, this is thought to be largely due to genetic similarities.

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People who share genes often have striking similarities in behavior and attitude. One study that examined 3,000 pairs of identical and fraternal twins found evidence for the genetic transmission of conservative views regarding topics such as socialism, church authority, the death penalty, and mixed-race marriage (Martin et al., 1986). It is very unlikely that a specific gene is directly responsible for a complex psychological outcome such as beliefs about social or political issues. Rather, a set of genes (or, more likely, many sets of genes interacting) may produce specific characteristics or tendencies to think in a conservative versus liberal manner. One study examined the DNA of 13,000 people and measured the extent to which they reported conservative versus liberal attitudes, and the study found associations between conservatism–liberalism and chromosomal regions linked to mental flexibility, or the extent to which people change their thinking in response to shifts in their environment, which could be one of the factors influencing our views on social and political issues (Hatemi et al., 2011). Current research by psychological scientists is aimed at better understanding how variations in our genetic code may contribute to the development of personality.

Traits in the Brain

What neurophysiological mechanisms might influence the development of personality traits? Eysenck (1967) speculated that extraversion and introversion might arise from individual differences in cortical arousal. Eysenck suggested that extraverts pursue stimulation because their reticular formation (the part of the brain that regulates arousal or alertness, as described in the Neuroscience and Behavior chapter) is not easily stimulated. To achieve greater cortical arousal and feel fully alert, Eysenck argued, extraverts seek out social interaction, parties, and other activities to achieve mental stimulation. In contrast, introverts may prefer reading or quiet activities because their cortex is very easily stimulated to a point higher than optimal alertness.

Behavioral and physiological research generally supports Eysenck’s view. When introverts and extraverts are presented with a range of intense stimuli, introverts respond more strongly, including salivating more when a drop of lemon juice is placed on their tongues and reacting more negatively to electric shocks or loud noises (Bartol & Costello, 1976; Stelmack, 1990). This reactivity has an impact on the ability to concentrate: Extraverts tend to perform well at tasks that are done in a noisy, arousing context (such as bartending or teaching), whereas introverts are better at tasks that require concentration in tranquil contexts (such as the work of a librarian or nighttime security guard; Geen, 1984; Lieberman & Rosenthal, 2001; Matthews & Gilliland, 1999).

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In a refined version of Eysenck’s ideas, Jeffrey Gray (1970) proposed that the dimensions of extraversion–introversion and neuroticism reflect two basic brain systems. The behavioral activation system (BAS), essentially a “go” system, activates approach behavior in response to the anticipation of reward. The extravert has a highly reactive BAS and will actively engage the environment, seeking social reinforcement and being on the go. The behavioral inhibition system (BIS), a “stop” system, inhibits behavior in response to stimuli signaling punishment. The anxious person, in turn, has a highly reactive BIS and will focus on negative outcomes and be on the lookout for stop signs.

Recent studies have suggested that the core personality traits may arise from individual differences in the brain. For instance, self-reported neuroticism is correlated with the volume of brain regions involved in sensitivity to threat; agreeableness with areas associated with processing information about the mental states of other people; conscientiousness with regions involved in self-regulation; and extraversion with areas associated with processing information about reward (DeYoung et al., 2010). Research aimed at understanding how the structure and activity of our brains can contribute to the formation of our personality traits is still in its early stages, but such research represents a growing area of the field that many believe holds great promise for helping us better understand how we each develop into the unique people that we are.