Differences in temperament exist in many other species. In a cross-species review of temperament in nonhuman animals, “extraversion” was the most universal. Seventeen out of nineteen studies identified a factor related to extraversion, such as sociability in pigs and dogs, “vivacity” in donkeys, or a “bold approach versus avoidance” dimension in octopuses. The reviewers point out that the manner in which temperament shows itself depends upon the species: “Whereas the human scoring low on Extraversion stays at home on Saturday night, or tries to blend into a corner at a large party, the octopus scoring low on Boldness stays in its protective den during feedings and attempts to hide itself by changing color or releasing ink into the water.” (Scientists find significant differences between octopuses on several dimensions of behavior, most consistently in levels of activity, reactivity, and avoidance. These differences show themselves early, by the third week of life, and researchers believe that the diversity of temperaments increases the likelihood that the octopuses will better adapt to their highly variable habitats, predators, and prey. Octopuses often live in exceptionally fluctuating near-shore environments that are subject to violent storms, extreme changes in tide and season, and pollution. Variability in temperament is also seen in animals that rely upon learning in order to adapt to changing circumstances; octopuses, it has been known for a long time, are good learners.)
Some species—rhesus and vervet monkeys, for instance, as well as hyenas and pigs—score particularly high on measures of curiosity, playfulness, and exploration. Primates vary a great deal from one species to another. Chimpanzees are more outgoing and impulsive than gorillas, who are shyer; rhesus monkeys are more exploratory and socially active than pigtail macaques. Primatologists speculate that species with the most diverse diets, those who must forage farther afield and actively defend against predators, need to be bolder, more curious, more energetic, and more exploratory than, for example, the less active fruit-eating monkeys.
Cats, dogs, and monkeys vary enormously within their own species in how fearful or bold they are in approaching new situations or unfamiliar individuals. Perhaps one house cat in seven, for instance, will avoid new situations and strangers and only unusually attack a rat. One in five young rhesus monkeys is easily distressed and fearful, a figure comparable to that found in human infants. Similar differences may also be seen in some species of birds and fish. Among zebra finches and pumpkinseed sunfish, for example, those animals most likely to explore novel objects are less likely to fly or swim in close proximity to other animals of their species; they are also more likely to be leaders, to forage independently and over a greater range, and to be better able to adapt to novel environments. They, by dint of their behavior, are also more likely to put themselves in danger’s way. The anthropologist Melvin Konner has discussed at length the importance of such risk-taking behavior in his excellent book Why the Reckless Survive. If an animal is designed for survival and reproduction, he points out, it is not designed for perfect safety.
Joyce Poole studied a family of twenty-four elephants in Kenya and found significant personality differences among them. Some elephants, she says, were “just plain boring,” others were timid, and yet others were “full of games and mischief.” She believes that some elephants are inherently “mercurial,” while others “just plod along.” One of the elephants she observed, for instance, a female named Ebony, was “always up for some mischief and full of life and exuberance most of the time.” Others were more phlegmatic and only intermittently ebullient.
Few animal researchers have looked at exuberance per se, although one intriguing study of brown bears living in an open area of sedge and flats on Admiralty Island in Alaska did assess “sparkliness,” “liveliness,” and “spiritedness.” Robert and Johanna Fagen, zoologists at the University of Alaska, collected data on seven adult bears during three years of summer salmon runs. “Sparkly” bears were defined as “bubbly, cheerful and full of sprightly movements.” “Spirited bears,” in like vein, were defined as “vivacious, animated and energetic, [approaching] life with abundant physical and mental energy.” The Fagens repeatedly rated the bears on a wide variety of measures and concluded that there are four general dimensions—liveliness, irritability, confidence with other bears, and fishing behavior—that best describe the personality of brown bears. They noted that although liveliness is an essential characteristic in bears, it is very little studied: “We find it interesting that a dimension (Lively) that includes lively curiosity and spirited movements, animation, flamboyance, sparkle, and a tendency to show off should emerge as a prominent feature of bears’ individual personalities.… It seems to measure qualities of behaviour and personality rather than absolute levels of activity or amount of movement. Previous studies of individuality in nonhumans and in humans did not report lively curiosity, spirited movements, or the other items included in our Lively dimension.” Rosemary Bolig and her colleagues at Ohio State University did find a related personality trait in rhesus monkeys, however, which consisted of opposing behavior patterns of “exuberance” and “nurturance” (the researchers referred to the monkeys with these qualities as “party animals” and “homebodies”). The exuberant animals were assessed by the researchers as highly active, curious, and playful; the nurturant animals, on the other hand, scored high on maternal and protective behavioral dimensions.
Extraversion in humans, extensive research shows, predisposes the individual to experience and display more positive emotions such as enthusiasm, interest, excitement, and joy. The relationship between positive emotions, or pleasant affect, and extraversion is one of the most consistent findings in studies of personality; it is also one of the strongest (the correlation between the two traits approaches 0.80 in several studies). Indeed, some psychologists have argued that positive emotionality is the glue that holds together the component parts of extraversion. Extraversion is also closely related to the number of close friends an individual has and to how likely he or she is to be selected for leadership roles. Extraverts as a group tend to be happier than their more introverted peers. The psychologists Ed Diener and Martin Seligman studied more than two hundred undergraduates, for example, and found that those students who described themselves as “consistently very happy” were much more extraverted than those who described themselves as less happy. It is to some extent a self-perpetuating phenomenon. Extraverts are gregarious and enthusiastic; such characteristics tend to be attractive to others and to create more opportunities for pleasure through greater contact with other people and the surrounding world. Enthusiasm itself leads to a more fervent engagement with ideas and an impassioned pursuit of interests.
Extraverts are not only more likely than introverts to experience positive moods, they also feel a greater intensity in such moods. In responding to questionnaires, they tend to agree with items like “When I feel happy it is a strong kind of exuberance,” “When something good happens, I am usually much more jubilant than others,” and “When I’m happy I bubble over with energy.” Introverts do not. In addition to experiencing more intensely positive moods, extraverts also feel and perform better in stressful and challenging circumstances.
People who are extraverted are more likely to act, to move, to engage. They lope, not amble; they fizz. They are like the infectiously exuberant writer Eugene Walter, who says, “We are the ones who gallop ahead two hundred miles and then stop and say, ‘What country is this?’ If we could organize, we would have taken over the world way back, but we are interested in so many things that when we head for California, we end up in Florida. You know. Our emblem is the centaur: half animal, half man. And shooting that arrow at the moon. Centaurs have all four feet on the ground, but that arrow is whizzing off to a distant planet.”
Why are some so vital and others not? Why do some people gallop full throttle into adventure while others fall back, fearful, intent on avoiding misadventure? There are many reasons, but the most notable differences in temperament are rooted in genetics an
d in the architecture and chemistry of the brain. Heredity unequivocably plays a critical role in temperament. Some individuals are simply more biologically predisposed to respond with fear when confronted with a new or uncertain situation; others are inclined to enjoy or investigate the unfamiliar. The genetic contribution to temperament, especially to extraversion, is strong. An analysis of 24,000 twins found that if one identical twin is an extravert, the other is very likely to be one as well. This is not nearly as true for fraternal (nonidentical) twins. (The correlation between identical twins is 0.5 or more, suggesting that at least 50 percent of extraversion is due to genetic factors. The correlation between fraternal twins is 0.2.)
Thomas Bouchard and his colleagues at the University of Minnesota examined identical twins who had been raised apart and found that if one twin was extraverted, the other twin, who had identical genetic material but a different environment of upbringing, was very likely to be extraverted as well (the correlation was high: 0.6). This gave strong support to the argument that there is a powerful genetic influence on temperament and that family upbringing has less of a determining role. “Joy, good cheer, and bubbliness,” the Minnesota researchers reported, were particularly heritable in their study. Studies of young children who are identical twins and who have been classified as having either an inhibited or an uninhibited temperament, analogous to extraverted and introverted temperaments in adults, also show correlations of between 0.5 and 0.6 for these types of temperament. If only those twins classified as extremely inhibited or extremely disinhibited are examined, the correlation is even higher, ranging between 0.7 and 0.9.
We are not so different from domestic dogs in our heritability and differences in temperament. All breeds of dog show a powerful genetic influence on behavior (again, generally in the range of 0.5). As with humans, there are significant differences in temperament between individual dogs within a breed, but there are also striking differences across breeds. The behavioral traits that most reliably differentiate breeds of dogs are excitability and general activity level, traits related to extraversion in humans. Basset hounds, for example, who would be on few judges’ lists for Most Exuberant in Show, are among the lowest scorers on both activity and excitability; terriers, on the other hand, are highly excitable and propulsively active. Breeds of dogs also vary enormously in the extent to which they demonstrate inhibited or excitable social behaviors, such as body and tail posture, tremor, exploratory and escape behaviors, and changes in heart rate. Some breeds are timid, others more curious or fierce. Swedish researchers studied behavior in more than 15,000 dogs of 164 species and found a major “personality” factor which consisted of playfulness, the tendency to explore, an interest in the chase, and sociability. This trait, which pervasively influenced the dogs’ behavior, is also observed in seven- to nine-week-old wolf pups. Confronted with a novel situation, the most fearless pups are also the most playful and exploratory. The shyer dogs, on the other hand, are uninterested in playing, more cautious, and less curious. The most exploratory and fearless pups, when tested a year later, are the most “dominant” within their pack.
There is little difference in playfulness between male and female dogs; studies of human children, on the other hand, find boys are more likely than girls to be physically spontaneous, to explore more and to explore larger areas, to engage in “rough-and-tumble” play, and to be less socially inhibited. Studies of adult humans also find that men are more likely than women to be energetic and to be perceived by others as enthusiastic and unrestrained.
Our species, like others, shows a wide diversity of temperaments: some of us rush toward the new and assume that it will bring pleasure, not wretchedness. As many at least step back from life, stay within a sprint of our foxholes, and watch as others make the forward moves. The disposition to advance or to retreat, to be enthusiastic or to be fearful, shows itself early in life. In a landmark series of studies, Jerome Kagan and his colleagues at Harvard identified temperament profiles in infants and young children that are strikingly similar to those seen in adults. Behaviorally inhibited infants and children, like introverted adults, will, when confronted with new people or new situations, actively avoid engagement with the unfamiliar. If they do approach, they do so slowly and reluctantly. They cling to their parents, are quieter, and move less energetically than their more extraverted peers.
Uninhibited children, on the other hand, readily initiate contacts with others, laugh and smile a lot, and are unusually talkative. They are extraverts in the making. A subgroup, perhaps one in ten of those studied by Kagan and his coworkers, displays an unusually high level of energy, smiles frequently, and laughs with “zeal.” This quality, the researchers conclude, is “difficult to name, for it is not captured simply by activity level. Other children run a lot but do not possess the enthusiasm and vibrancy that is distinctive of these children. The term vitality comes closest.” The Harvard scientists found that this characteristic manifests itself at a remarkably young age. At four months, the infants who show a vibrant and positive mood also babble and smile a lot, exhibit little or no anxiety, and are “utterly fearless.” When examined more than ten years later, these high-mood and high-energy infants—whom Kagan calls “Ethel Merman types”—are very likely to have remained extraverted and energetic.
Uninhibited children, in addition to being more exuberant, are far more likely to take risks than those who are inhibited. In a study of five-and-a-half-year-olds, for example, children were asked to choose the distance from which they preferred to throw a ball into a basket. The inhibited children opted to stand very close to the basket, only one or two feet away. The uninhibited children, on the other hand, more often chose to stand four or five feet back. The investigators noted that these children looked as though they enjoyed the greater challenge.
Nathan Fox, of the University of Maryland, describes a group of highly energetic and enthusiastic infants whom he and his colleagues have studied. Characterized by the researchers as “exuberant,” these infants are highly and eagerly reactive to novelty; they smile, coo, and gurgle a great deal, are sociable and enthusiastic, and seem exceptionally eager to explore the world around them. They show little fear in unfamiliar situations. “From the youngest age,” the researchers observe, “these infants appeared to exhibit exuberance for novelty and social interaction that was unique.” Their description of the moods and behaviors of these exuberant infants was strongly confirmed by the observations made by the children’s parents. Fox and his colleagues found, as Kagan did, that the “exuberant” infants made up about 10 percent of those they studied.
The psychologist Ellen Winner, who studies artistically and intellectually gifted children, states that even in infancy exuberant children show very high energy levels and are unusually alert and curious. “From an early age,” she writes, “these children find things that interest them and they throw themselves into these domains.” One eight-year-old child she studied “created hundreds of soldiers, each wearing a uniform of a particular country and rank (which he learned about by reading). He made these soldiers out of paper. When he was finished with this project, he created hundreds (literally) of zoo animals, each one very realistic, and designed cages for them.” She describes his behavior as exuberant, she says, because “he became completely immersed in this activity for months, it required high energy, and it clearly gave him pleasure. He lived in his own private world.”
Many studies find a strong positive relationship between curiosity, a preference for novelty, and subsequent measures of intelligence and academic performance. Infants who gaze more at novel objects, for example, score higher on later tests of cognitive ability. (Likewise in our primate cousins. Curiosity predicts successful problem-solving in small-eared bushbabies.) Shy and anxious children, who tend to avoid novel objects or situations, perform less well on tasks measuring creativity. Seeking out novelty shows itself early. Researchers at the University of Southern California tested the tendency to seek out stimulation
in 1,795 three-year-olds and then assessed their cognitive abilities when they were eleven. Children who scored high on stimulation-seeking when young—defined by the researchers as greater exploratory behavior away from their mothers, more friendliness and talking to strangers, and more active social play—scored significantly higher on IQ tests (12 points). They also had higher scholastic and reading ability than the children who had scored lower on stimulation-seeking.
There are several possible explanations for this unusually strong correlation (0.5 to 0.9) between an active, curious temperament and cognitive ability. Young children who are shy or anxious may so fear criticism from others and be so desirous of pleasing that they do not take the risks necessary to enhance their lives of play and imagination. These children, often more afraid of failing than excited by the chance of winning, put such a premium on “getting it right” that they limit their exploration of the field of possibilities. Young children who seek out novelty or actively explore the world around them, on the other hand, create a very much enriched environment in which to learn. They are probably innately more highly energetic and motivated, as well. Research indicates that curious, enthusiastic, and cheerful children also have a more positive effect on their parents, as well as on other children, teachers, and other adults. This in turn positively affects the child’s overall social and learning environment. Exuberant children create more complex and rewarding environments for themselves than do shyer, more timid children.