Making the Connection: Strategies to Build Effective Personal Relationships (Collection) (59 page)

Useful though this may be, it is important to remember that the Top Ten are not sharply defined natural categories. For example, there are all kinds of narcissistic bosses. Nevertheless, identifying someone as narcissistic, using the characteristics I’ve described, still communicates real content that further observation and analysis can either confirm or reject. The same is true for the other patterns on the list.

When viewed in this way, the hunch that a person has a potentially troublesome pattern can be a useful starting
point for thinking about all his or her notable Big Five traits. In the case of narcissism, it might first focus your attention on the facets of low A that tipped you off. If your hunch is confirmed, Conscientiousness might be the next one to consider: High C can propel people with the narcissistic pattern to great achievements, while low C may move them in an antisocial direction. Rankings on N, O, and E also change the complexion of this pattern in many different ways. So building a Big Five assessment around an initial hunch about someone can be more fruitful than just going through the list of traits without a working hypothesis.

As you learn to think of people in terms of both their traits and their patterns, you will not only start seeing them more clearly—you will also become increasingly aware of the great variety of human personalities. This raises questions about the origins of these many variations, questions that I turn to in the following chapter.

Part II: Explaining Personality Differences

Every night and every morn

Some to misery are born,

Every morn and every night

Some are born to sweet delight.

—William Blake,
Songs of Innocence

Three. How Genes Make Us Different

In considering the cast of characters I described in the last chapter, you may have wondered how they got to be so different. If you’re like most people, you probably assumed that their personality patterns were mainly caused by social circumstances and upbringing. But it’s likely that you also toyed with another explanation that is becoming increasingly popular: genes.

The growing interest in the genetics of personality is reflected in its extensive media coverage. Consider, for example, this excerpt from a
New York Times
column about the genetics of excitement-seeking:

Jason Dallas used to think of his daredevil streak—a love of backcountry skiing, mountain bikes and fast vehicles—as “a personality thing.” Then he heard that scientists at the Fred Hutchison Cancer Research Center had linked risk-taking in mice to a gene. Those without it pranced unprotected along a steel beam instead of huddling in safety like the other mice. Now Mr. Dallas, a chef in Seattle, is convinced he has a genetic predisposition for risk-taking, a conclusion that researchers say is not unwarranted, since the similar variations in human
genes can explain why people perceive danger differently. “It’s in your blood,” Mr. Dallas said. “You hear people say that kind of thing, but now you know it really is.”
¹

What I find remarkable about this report is that Jason Dallas so readily accepts the idea that a gene that affects the personality of a mouse may also affect his own. Although there is no evidence that the gene in this study,
²
neuroD2, has anything to do with his love of excitement, Dallas has been primed to make this connection by the widely publicized findings that there is, in fact, a close relationship between mouse genes and human genes, and between mouse brains and human brains. Needless to say, there are also important differences. But as I show in this chapter, Dallas does have good reason to believe that his daredevil streak has some genetic basis, even though his neuroD2 may have nothing to do with it.

The belief that some personality traits are innate is hardly new. What is new is our growing understanding of the degree and nature of this genetic influence. In this chapter, I take you beyond the vague idea that genes affect personality, to a deeper conception of the role they play in making us who we are.

A New Foundation for Psychology

Charles Darwin, who revolutionized our understanding of the origins of personality differences, didn’t begin with a particular interest in this subject. He was after something much bigger: the origin of
all
the differences among
all
living things. Of the clues that led him to that answer, the most revealing came from domestic animal breeding.

Dogs were especially informative. People already knew in Darwin’s time that breeds as different as greyhounds and spaniels descended from the same wild ancestors. Darwin also understood that their selective breeding depended on the transmission of inherited characteristics from parents to pups, and that new breeds arose “by the careful selection of the individuals which present the desired character.” Furthermore, the creation of strikingly different breeds was a gradual affair, accomplished through a succession of little steps. As Darwin explained this in 1859 in
Origin of Species
:

[W]hen we compare the many breeds of dogs, each good for man in different ways ... we cannot suppose that all the breeds were suddenly produced as perfect and useful as we now see them; indeed, in many cases, we know this has not been their history. The key is man’s power of accumulative selection: nature gives successive variations; man adds them up in certain directions useful for him. In this sense he may be said to have made for himself useful breeds.
³

Once Darwin recognized that the creation of dog breeds depends on the breeder’s selection of heritable variations, it occurred to him that nature does the same thing: It selects those heritable variations—spontaneous modifications of genes, now called mutations—that are advantageous in the wild. This process of natural selection ensures that desirable mutations are passed on from generation to generation and may eventually become stable features of the species.

A good example is a mutation in a gene, SLC24A5, that controls the deposit of melanin, a black pigment. What makes this mutation so interesting is that it caused a dramatic change in the color of human skin, from black to white. In sunny Africa black skin is favored to block harmful ultraviolet rays while still allowing enough through to stimulate the skin’s production of vitamin D. This explains why the native African population has SLC24A5 genes that provide lots of black pigment. But in regions far from the equator, where sunlight is scarce, a mutation that inactivates this gene
⁴
took over because the pale skin that results lets through more of the limited light to make vitamin D.
⁵
As with the evolution of many other human differences, this one became prevalent through accidental DNA mutations and natural selection based on adaptation to specific environmental conditions.

Darwin wasn’t in a position to provide such a persuasive illustration. But this didn’t stop him from extending his idea from biology to psychology. It was clear to him that selective breeding affected not only physical characteristics, but also behavioral ones. For example, breeders have selected dogs not only for their shape and size, but also for their skills, such as herding or pointing, and for personality traits such as agreeableness or aggressiveness. So why wouldn’t natural selection of behavioral traits also increase fitness in the wild? By the end of
Origin of Species,
Darwin was sufficiently convinced of this to predict that “In the distant future...psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation.” To put this in modern terms, Darwin predicted that
our understanding of psychology would one day rely on knowledge of the genetic variations that affect behavior.

But Darwin was initially reluctant to extend this prediction from animals to people. The mere hint that physical features of humans had animal origins would cause him trouble enough. He would, for some time, leave human psychology to others.

Experiments of Nature

The man who first took up the challenge was Darwin’s cousin, Francis Galton, whom you met in
Chapter 1
, and he was willing to take it even further. It seemed to Galton that if the characteristic behaviors of a species are inherited, the behavioral differences between individual people—our distinctive intellectual abilities and personality traits—might also be inherited.

Such variations in human talents and traits were already of great personal interest to Galton. A precocious child who was proud of his intelligence and achievements, he had long believed that both he and Charles Darwin had inherited their special gifts from their common grandfather, the distinguished physician and scientist Erasmus Darwin. But Galton was aware that his family also provided him with a privileged upbringing that fostered whatever gifts he inherited by placing him “in a more favourable position for advancement than if he had been the son of an ordinary person.”
⁶
So was he gifted because of favorable heredity or favorable upbringing?

To address this question, Galton turned to an experiment of nature: twins. Galton knew that some twins looked so much alike that they were probably genetically identical, whereas others were no more similar than siblings born at different times. Because both identical and fraternal twins were usually raised together by their parents, the members of each pair would have a comparable upbringing. If he found that the behavior of identical twins was more similar than that of same-sex fraternal twins, this would support his hunch that greater genetic similarity leads to greater behavioral similarity.

In 1875, Galton reported that 35 sets of identical twins showed much greater behavioral similarities than 20 sets of fraternal twins, which he took as support for the importance of heredity. In “The History of Twins As a Criterion of the Relative Powers of Nature and Nurture,” he announced, “[T]here is no escape from the conclusion that nature prevails enormously over nurture.”
⁷
His observations that adopted children of gifted adoptive parents are no more gifted than ordinary children, even though they are provided with a privileged environment, also supported this conclusion.
⁸
This was the first use of another natural experimental approach—adoption—in assessing the role of inheritance and upbringing.

Although Galton’s ways of studying behavior were crude, his results were sufficiently persuasive to convince his most eminent critic. As Darwin wrote to him after studying some of Galton’s publications, “I do not think I ever in all my life read anything more interesting and original—and how well
and clearly you put every point! ... You have made a convert of an opponent in one sense, for I have always maintained that, excepting fools, men did not differ much in intellect, only in zeal and hard work.”
⁹
While Darwin’s praise was not wholly merited in its time, it was subsequently justified by more persuasive research using Galton’s approach.

How Much of Our Personality Differences Is Heritable?

The biggest impediment to Galton’s research is that he didn’t know how to measure personality differences. He had tried to make objective assessments in his work with twins, but he was painfully aware that his methods weren’t very good. Frustrated by these difficulties, Galton turned his attention to the inheritance of height, which he could measure accurately. His studies of the relationship between the heights of parents and their children led him to develop the formula for calculating correlations that I mentioned earlier, and that was later adapted to create the Big Five personality tests.

The Big Five tests are just what Galton had hoped for, and they are now routinely used to investigate the influence of genes on the personalities of identical and fraternal twins. In a typical study, each twin is given a Big Five test, and the scores are compared with those of the other twin. If genes influence these personality traits, both twins should have scores that are somewhat similar. But the similarities of pairs of identical twins, who share 100% of their genes (because they are derived from a single fertilized egg that split after conception), should be twice as great as the similarities of
same-sex fraternal twins (derived from different eggs), who share only 50% of their genes.

This is just what researchers have found. For example, in a study using hundreds of subjects, the Extraversion scores of the two members of a pair of fraternal twins had an average correlation of 0.23 (on a scale of 0 to 1). In contrast, the two members of a pair of identical twins had an average correlation about twice as large, 0.48. The difference in correlations (0.48 − 0.23 = 0.25) is assumed to reflect the difference between having all the same genes (identical twins) and having half the same genes (fraternal twins). Therefore, this difference measures only half the effect of having all the same genes. To get the full effect, which geneticists call heritability, 0.25 is doubled to get 0.5, or 50%.
¹⁰
Studies of Agreeableness, Conscientiousness, Neuroticism, and Openness also found heritability to be around 50%.
¹¹

When the evidence for such substantial heritability of personality traits was first published, critics pointed out another possible explanation for the greater psychological resemblance of the identical twin pairs. Instead of resulting from genes alone, it might also result from the identical twins being treated more alike than the fraternal twins. Fortunately, the contribution of shared family environment can be evaluated through another experiment of nature: studying identical twins separated after birth and raised in different families.