The Story of Psychology (66 page)

As a researcher, Sheldon spared himself no pains: he photographed no fewer than four thousand male college students in the nude and recorded their key physical measurements. From this mass of data he concluded that there are three basic body types much resembling Kretschmer’s: the
endomorph
, soft, rounded, and plump; the
mesomorph
, hard, square, big-boned, and muscular; and the
ectomorph
, tall, thin, and large of skull. These types, he believed, represent the special development of one or another of the three layers of cells that first differentiate in the embryo: the endoderm, from which arise the digestive tract and internal organs; the mesoderm, from which come bones and muscles; and the ectoderm, from which develops the nervous system.

To show the relation of personality traits to these somatotypes, Sheldon administered personality tests to two hundred of his subjects, and over the years gathered a wealth of other trait data from extensive interviews and his own observations of behavior. He found, as he had expected to, that a characteristic personality pattern was associated with each somatotype. The short, plump endomorph is usually social, relaxed, talkative, and sybaritic; the well-balanced mesomorph is energetic, assertive, courageous, optimistic, and sports-loving; and the tall, thin ectomorph is introverted, shy, intellectual, inhibited, and unsociable. Sheldon hypothesized that the genes determine which somatotype prevails as the fetus develops and thus which personality pattern the person manifests.
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His major publications, appearing in the 1940s, aroused much public and professional interest. But most psychologists found Sheldon’s typology
simplistic and his research methods faulty: he paid little attention to the socio-economic background of his subjects, although a child of poverty is hardly likely to grow up a fat, jolly endomorph or a child of wealth and advantage a shy, cerebral ectomorph. Psychologists were particularly leery of the extremely high correlations—+.79 to +.83— Sheldon reported between the three somatotypes and their associated personality types. Correlations of that magnitude are so unusual in psychology, where most phenomena have multiple causes, as to suggest a fundamental flaw in research design. And indeed there was one. To quote one eminent authority, Gardner Lindzey:

Supporters of Sheldon’s views sought to repair this shortcoming in later studies; they had the somatotype ratings made from photographs by raters who never met the individuals, and the personality evaluations made by other raters from questionnaire data rather than interviews. These studies confirmed Sheldon’s connections between body type and personality, but with considerably smaller correlations.
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Even these data, however, might not prove a direct link between somatotypes and personality; the link could be indirect and social. Because people expect strong muscular mesomorphs to be leaders, weak skinny ectomorphs to avoid physical competition and rely on their minds, children, sensing what people expect of them, may come to behave accordingly.
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Although the somatotype theory attracted attention and sparked much research during the 1950s, the trenchant criticisms of it, and the fact that the theory was hereditarian and thus out of tune with the prevailing liberalism of the time, caused it to fade in influence. By the 1960s, according to the distinguished historian of American psychology Ernest Hilgard, it had almost vanished from the scene. But stronger evidence of the innateness of personality, or of at least a predisposition toward one pattern or another, has continued to crop up.

In the 1940s, Alexander Thomas and Stella Chess, psychiatrists at the New York University Medical Center, began studying individual temperamental
differences in infants and young children. (“Temperament,” a part of personality, is the individual’s characteristic way of reacting emotionally to stimuli and situations.) Thomas and Chess collected data on babies’ behavior starting at birth, partly by personal observation and partly by asking parents specific questions, such as how the infant reacted to the first bath or the first mouthful of cereal. They found good evidence of what every mother of more than one child knows, namely, that infants are temperamentally different from one another from their first hours on.

After years of study, Thomas and Chess specified nine differences that are manifest from the beginning of life. Some babies are more active than others; some have regular rhythms of eating, sleeping, and defecating while others are irregular and unpredictable; some like everything new (they gobble up the first spoonful of new food) while others do not (they spit it out); some adapt quickly to change, while others are distressed by any alteration of their schedules; some react to stimuli strongly, either laughing or howling, while others only smile or whimper; some are happy most of the time, others unhappy; some seem aware of every sight, sound, and touch, while others respond only to some stimuli and ignore others; some can be easily distracted if they are uncomfortable, but others are more single-minded; and some have a good attention span and will play with one toy for a long time, while others shift quickly from one activity to the next.

Summing up, Thomas and Chess found that about two thirds of all babies show a characteristic temperament early in infancy. Four out of ten are “easy” (placid and adaptable), one out of ten is “difficult” (irritable and hard to pacify), and one out of six is “slow to warm up” (moderately fussy or apprehensive but able to get used to things and people).
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As Thomas and Chess watched some of the children develop to near adulthood, they were initially impressed by how often the temperament of a baby remained substantially unchanged in childhood and adolescence. Later, their more detailed findings led them to a more qualified conclusion. Frequently, some or many aspects of the basic temperament were modified by such major events as a serious accident or illness, or such changes in the environment as the death of a parent or a dramatic alteration in the family’s economic status. But when there were no such events or changes in the environment, the temperamental style of the first days of life was likely to be the temperamental style of the grown person.
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Even more impressive evidence that personality is partly innate has
come from research in behavior genetics. This specialty, formerly somewhat outside mainstream psychology but now becoming more central to it, deals with genetic influences on psychological characteristics. Its major method of inquiry, originated by Galton, is to see to what extent people related to each other in differing degrees have similar mental abilities, personality, and achievements. First cousins have an eighth of their 25,000 to 30,000 genes in common, siblings a half, and identical twins all. If genes exert an influence on psychological development, the closer the genetic relationship between two people, the more psychologically alike they should be.

A vast amount of research conducted over the past half century has shown this to be the case. Some studies have shown that the closer the genetic relationship, the more alike the people are in mental health or illness.
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Others have found the same to be true of general intelligence and of specific mental abilities.
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And in the past three decades a number of geneticists and psychologists have found that the closer the genetic relationship, the more alike the personalities of the individuals.

Some of the personality research is based on analyses of the correlations in the traits of fraternal twins and of identical twins; consistently, the identicals are much more alike than the fraternals. Still, if they have been reared together in the same home, the evidence is less than perfect; they have had the same or very similar environmental influences all along (and identical twins, in particular, are even treated alike by their parents). For that reason, the best data—but the hardest to gather because instances are so rare—come from studies of identical twins separated at or soon after birth and raised in different homes and areas, where the environments are at least somewhat dissimilar.

Consider the case of Jim Lewis and Jim Springer, identical twins who were separated a month after their birth in 1940 and reared forty-five miles apart in different families in Ohio. They were totally unaware of each other’s existence until 1979, when they were thirty-nine. In that year they met, but not by accident. They had been tracked down by Professor Thomas Bouchard, director of the Minnesota Center for Twin and Adoption Research at the University of Minnesota, who was conducting a study of fraternals and identicals reared apart. Jim Lewis and Jim Springer, except for their clothing, were physically indistinguishable, as are almost all pairs of identicals. Remarkable as this always seems, what was far more remarkable were other similarities. Both men had wives named Betty, were heavy smokers of Salems, drove Chevrolets, bit their fingernails, and had dogs named Toy.

This sounds as if it had been concocted by a writer for one of those supermarket tabloids filled with accounts of such wonders as babies borne by eighty-year-olds. But the story was not concocted. Of course, some of the peculiar coincidences may have been due to the twins’ living in the same part of the country, others to chance. What was more important was the evidence adduced by psychological testing. Bouchard and his research team put the twins through a battery of personality tests and found their responses and trait scores nearly identical.
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From 1979 to 1990, Bouchard and his researchers tracked down nearly eighty pairs of identicals and thirty-three pairs of fraternals reared apart (out of some eight thousand pairs in their files), and put each twin through about fifty hours of intensive tests and interviews. For comparative purposes, they did the same with a number of identical and fraternal twins reared together. Statistical analysis of all the correlations within the twin pairs and among these various groups led the team to conclude that about 50 percent of variance in personality is due to heredity.
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(They reported similarly remarkable findings for many other psychological variables, including general intelligence, language ability, social attitudes, homosexuality, substance abuse, and even religious interests.)

Some other studies in behavior genetics, however, have yielded more modest estimates. John C. Loehlin, of the University of Texas, Austin, recently reviewed a large number of twin studies and found that on the whole the evidence indicated that heredity accounts for about 40 percent of the variance in personality.
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Several studies comparing adopted children to their adoptive mothers and to their biological mothers found only 25 percent of the variance attributable to heredity (although, interestingly, the adopted children resemble their biological mothers more than those who reared them in personality).
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Clarifying the matter, in 2003 Bouchard and a colleague, Matt McGue, performed a comprehensive review of Bouchard’s and other researchers’ twin, family, and adoption research. Sophisticated mathematical analysis produced cumulative evidence that “genetic influence on personality trait variation is in the 40%–55% range” and that “common (shared) family influence on personality traits is very close to zero.” Nonshared—that is, different—environmental influences account for much or most of the other personality variations, but have been extremely difficult to identify.
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The figures do not mean that 40 to 55 percent of any individual’s personality results from hereditary influences. Variance refers to the range
of differences among people in any trait or set of traits. Data from Bouchard’s center show, for example, that if a group of adults range in height from, say, four feet to seven feet, 90 percent of that span of differences is due to heredity, 10 percent to environment. Similarly, the twin studies mean that 40 to 55 percent of the range of personality differences among any group of people are of hereditary origin. This may explain why Americans have so many more variations in personality than the members of a more genetically homogeneous population, like the Japanese.

The findings of behavior genetics yield new understanding on a theoretical level—a level very different from that which interests most personality psychologists, namely, insight into the emotions and social relations involved in personality, and ways of testing and influencing them. It is even possible to see behavior genetics as diminishing the hope that psychology can improve the quality of human life, since to the degree that personality is hereditary in origin, it is not amenable to parental or social influence, therapy, or any other potentially controllable environmental factor. Many psychologists, therefore, including those in the field of personality, consider the findings of behavior genetics valuable as science but of no benefit in practice. What matters to them is the rest of variance in personality—the extent to which it can be influenced for better or worse.

Personality is no longer the most prominent field of psychology, not because it has shrunk in size but because by a generation ago certain newer fields had expanded and become the foci of attention. Also, as in any mature field of science, many personality researchers now churn out overspecialized studies of minutiae; happily, some others are still doing expansive and exciting work.

Among the more interesting developments in the field has been the study of the influence of personality on “well-being” (the general sense of contentment) in the middle and later years. Paul T. Costa and Robert R. McCrae, working with people enrolled in the Baltimore Longitudinal Study of Aging, a long-running research project of the National Institute on Aging, found that extraverts, who score high on such traits as sociability, general activity, and “ascendance” (similar to dominance), were happier in midlife and beyond than most introverts. They also found that
people who score low on neuroticism adapted better to the changes of middle age and old age than people who score high on neuroticism (measured by such traits as chronic anxiety, hostility, self-consciousness, and impulsiveness). The latter were likely to see the problems of middle age as a crisis, worry about their health, be frustrated and disappointed by retirement, and be at risk for depression and despair.
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