After reading this debate on stability versus change, explain the debat

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Why Are Some People Different From Others? Understanding the Causes of Personality

In the previous chapter, we discussed some of the major theories of personality. In particular, we examined the so-called “trait approach,” which many personality experts see as the most useful approach for examining

individual differences in personality. Within this approach, the Five Factor Model (FFM) has become the global language for describing both differences and similarities between people’s consistent patterns of behavior, thought, and emotion; Just as we measure a region’s climate in Celsius or a person’s height in meters, we can describe what a person is like by reference to his

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or her Extraversion, Neuroticism, Openness, Agreeableness, and Conscientiousness levels (though laypeople will use less techni- cal terms for each of these factors). Indeed, the FFM provides a rather general classifi cation of human personality, enabling us to compare people from every culture, as well as within a given society. So, when we hear someone say “my friend and I are very similar,” the FFM enables us to assess “how” (for instance, we are both sociable or extraverted).

In addition to the question of how people differ, however, personality researchers also want to know why. For example, we could ask ourselves why some people are talkative and outgoing, while others seem shy and reserved. Or, why some are relaxed before an exam or comfortable in front of a crowd, while others experience anxiety when facing those situations. These questions refer not to how a person behaves (and thinks or feels) but rather to why they behave the way they do. That is, what is the reason behind a person’s extraverted, agreeable, or conscientious per- sonality? Is it the way they were brought up by their parents? Is it the school they went to and the education they received? Or is it perhaps simply the genes they inherited from their extraverted and agreeable mother or conscientious father? Questions about the causes of personality allude to one of the oldest debates in psychology, namely the nature versus nurture debate.

When we refl ect upon these questions, we wonder to what degree we may be biologically predisposed to act in certain ways. Laypeople tend to believe that personality simply refl ects the various life experiences that we are exposed to, such that a person’s character is the result of his or her life experiences. In contrast, more and more personality researchers seem obsessed with emphasizing the genetic and biological factors underly- ing individual differences. From twin studies to molecular genetic studies, the quest for the biological basis of personality has excited a growing number of personality psychologists and neuroscientists. As will be seen in this chapter, although there is mixed enthusiasm among the wider psychological commu- nity about the success of this enterprise, it is quite clear that

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nurture and nature are not mutually exclusive, but that they interact and have reciprocal effects. Around the time this book was being written, a student of psychology approached one of us after a class and asked: “Can people change their personali- ties?” This is an important question from the standpoint of sci- entifi c inquiry, of course. However, many people will probably also fi nd this question to be personally relevant. After all, most of us have at least one bad habit that we would like to change (if you don’t think that’s your case, you may be a narcissist . . . or perfect). Many people would also like to change some generic aspects of their behaviors; for instance, how proactive they are, how organized they are, how confi dent they are, how kind or ruthless they are, and so on. These concern changing at least some aspects of our personality.

It is interesting to note that self-improvement products and services constitute a vast (and growing) market, particularly in the western world. According to a market report, the U.S. self-improvement market is worth $9.6 billion, with annual growth rates reaching 25% (Marketdata Enterprises, 2005). To some extent, most of these products and services are focused on personality change: how to change one’s ways of doing things, thinking about things, or feeling about them. Some very popu- lar self-help books will tell you to acquire new habits—habits that are common to all successful people (Covey, 1989). Others will tell you that “anyone can do it” (Bannatyne, 2007). The message here is often to be more determined, more assertive, more in control, less negative, and so on. In brief, self-help prod- ucts tell us that we can change the way we think, the way we feel, and the way we act; they tell us that we can change our per- sonality. The fact that these products and services are so popular indicates that the question of change in itself may be a very sig- nifi cant and personally relevant one for a lot of people. So, the question for psychological and empirical enquiry, therefore, is as follows: Can people change?

While the answer may be complex, people are often divided between one of two opinions: nature or nurture. That

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is, for some, personality is determined by biological factors and people cannot change. A shy person will always be shy, a lazy person will always be lazy, and a disorganized person will always be disorganized. Others believe that personality is formed through various life experiences and by the environ- ment, which means that people can indeed change (whether they actually do is a different question). A shy person can become outgoing and assertive, a lazy person can become hardworking and determined, and a disorganized person can become disciplined and effi cient. Unfortunately, however, the relationship between nature and nurture is not as straightfor- ward. As you will see, there are additional and differing ways in which nature and nurture can interact to “form” personality (i.e., stable patterns of behavior, thoughts, and feelings), and the causality underlying this relationship is not always one- directional.

The aim of this chapter is twofold: fi rst, to describe the main causal theories of personality, which deal with the ques- tion of why; that is, why people differ in various ways. Second, and following from the fi rst point, to address the question of personality change and development; that is, whether people can change, and if so, the extent to which they actually do. In the fi nal section, we will discuss the main factors that contrib- ute to change.

GENES AND PERSONALITY

To tackle the fi rst question of why personality differences between people exist, psychologists have generally occupied three different fi elds of investigation: the genetic, the biochemi- cal, and the evolutionary. While these paradigms are all focused on the nature part of the argument, they are useful for assessing the relative infl uence of both biological and environmental fac- tors on personality.

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While psychologists have been interested in the biologi- cal/genetic underpinnings of personality since the times of the ancient Greeks, the greatest progress in this area has been made only in the past 50 to 60 years. The most successful and infl u- ential of these attempts have undoubtedly been in the fi eld of behavioral genetics. Nevertheless, more recent research within molecular genetics and evolutionary psychology has contributed a great deal to our understanding of the biological roots of per- sonality. Before we outline the major fi ndings from each of these fi elds, however, it is useful to delineate some basic principles of the discipline of genetics.

Genetics as a discipline deals with the molecular structure and function of genes. Everything we inherit—traits that are common to all people and those that are unique to only one person—is passed through biological components known as genes. When we talk about inherited traits, we often refer to physical attributes, such as hair color, eye color, and height, because these are traits we can observe. Nevertheless, the dis- cussion of heritability, as we will see, is not limited to physical traits, and extends also to psychological traits.

As everybody knows, genes are passed onto us by our bio- logical parents. We inherit 23 pairs of chromosomes—one of each pair from each of our biological parents—and these chro- mosomes are made up of thousands of genes. A core function of genes is to synthesize proteins that build, maintain, and regu- late our bodies. In most basic terms, therefore, genes can be seen as basic bodily components that direct the biological develop- ment of the organism. Given that around 99.9% of the genetic makeup is identical for all people (indeed humans and chim- panzees share roughly 98% of their genes), minute differences in how certain genes synthesize proteins appear to somehow snowball into visible behavioral differences between individu- als (this is the bit we observe or measure). However, we should note that genes do not infl uence behavior directly. That is, there is no gene causing differences in intelligence or Extraversion between people. Rather, genes infl uence behavior and

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psychology indirectly, by affecting the biological functioning of the body (e.g., nervous system, hormonal regulation, etc.).

Behavioral Genetics

Now that we have outlined some basic components of the human genome, we will provide an overview of the three dis- ciplines that have informed our understanding of the causes of personality, starting with behavioral genetics.

Behavioral genetics is an area of psychology concerned with the assessment of the relative contribution of genetic and nongenetic infl uences on various individual variables of dif- ference, including personality, intelligence, and psychological disorders. It attempts to estimate the degree to which indi- vidual differences are the product of experience (e.g., learning, education, acquired values, etc.) or of “genetically imprinted” information.

One of the salient psychological traits examined in behav- ioral genetics research is intelligence or cognitive ability. Indeed, the link between genetics and intelligence remains one of the most controversial topics in psychology. This is hardly surpris- ing: If we acknowledge that there are individual differences in intelligence, a natural question that follows is “Why?” Put dif- ferently, if we accept that some people are smarter than others, then the question is as follows: Are these individual differences caused by genes or by the environment?

One problem is that common sense is pretty useless when it comes to answering this question. Consider, for instance, the rather typical case of a family of four—two parents and two children. Imagine that the parents in this family are very bright and wealthy. Imagine, in addition, that the children in this family also are very bright. Would that be suffi cient evi- dence for the fact that the children’s intelligence was inherited from their parents? Although one would certainly think so in the case of height, eye color, and other physical traits, when it comes to intelligence or psychological traits, the answer could

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be different. Indeed, an equally plausible explanation for the higher intelligence levels of these children would be that they have received a good education because of their higher socioeco- nomic status. Furthermore, it would also be possible that their parents exposed them to books, quizzes, academic tasks, and other intellectually stimulating environments, which nurtured their levels of intelligence. Thus, the children’s intelligence may, in actual fact, have little to do with genetic inheritance, but rather have indirectly been affected by the upbringing provided by the smart parents.

As you can see from this scenario, the question has two plausible answers—and the same problem applies to personal- ity and other psychological traits. We could say that a person is more sociable, assertive, and determined than another, because of his or her genes. On the other hand, we could also argue that it is because they were raised in a competitive environment, where they had to fi ght for attention and failure was not an option. Again, logically, both arguments may be equally valid. So, how can we determine whether a psychological quality is inherited or not? This question concerns a more fundamental issue in science, namely the difference between prediction and explanation. So, while it is common sense that children are more likely to resemble their parents in personality and intel- ligence, the reasons for this may not be obvious. In other words, although we can predict a child’s personality and cognitive abil- ity profi le from their parents’ profi les, there are different expla- nations for that association.

The task of behavioral geneticists is to determine the rela- tive contribution of genetic heritability and environmental infl uences. To do this, they employ two main research meth- ods: twin studies and adoption studies. Twin studies provide a very convenient and scientifi cally rigorous way to determine biological versus environmental effects. They are often referred to as “experiments of nature” because they enable researchers to capitalize on the systematic differences that exist between identical and nonidentical twins. Identical or monozygotic twins

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develop from the same fertilized egg and therefore share 100% of their genes, whereas nonidentical or dizygotic twins develop from two separately fertilized eggs and share around 50% of their genes (this is the same amount as siblings share with each other, and parents share with their children). Thus, by compar- ing identical and nonidentical twins, researchers are able to “manipulate” (though naturally rather than experimentally) the genetic variability between individuals, while keeping con- stant the environmental variability (i.e., the environment that the twins shared as they were growing up). It follows that if there is a genetic underpinning for personality, then identical twins should be more alike than nonidentical twins, because they have a higher genetic resemblance. If identical twins display no more similarity to one another (in terms of their personal- ity, IQ, or any other trait) than do nonidentical twins, then we can conclude that genes are not involved in the formation of that trait and that the environment is therefore the sole cause of individual differences in personality.

The alternative method for determining whether person- ality is inherited or not is adoption studies. Adoption studies are often referred to as “experiments of society” because they allow researchers to manipulate the environmental variability, while keeping constant the genetic variability. To illustrate this method, consider a child, Jasmine, who is separated from her biological parents and siblings immediately after birth. She is adopted by another family (i.e., her adoptive family). Imagine that the adoptive parents also have two biological children. After many years, Jasmine, who is now a grown woman, is reunited with her biological family. They meet for the fi rst time in more than 20 years. Now imagine that a group of psycholo- gists, as part of a research study, administer a personality test to Jasmine and the members of both her adoptive and biological families (i.e., parents and siblings of both families). She has not met her biological family since she was an infant. The question is as follows: Would we expect Jasmine to be more similar to her adoptive parents or her biological parents?

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As you can probably see, such case studies are extremely useful for examining the relative contribution of genes and of the environment on personality differences. It follows that if environment and upbringing exert the main infl uence on a person’s personality, then Jasmine should be far more simi- lar to her adoptive family members than her biological fam- ily members. If genes exert the main infl uence, the opposite should be true.

A more robust but rather rare variation of this method involves doing research with identical twins reared apart (i.e., separated at young age). In these studies, we have biologically related individuals who share 100% of their genes but have been exposed to completely different environments for most of their lives. Again, if the environment and life experiences are central to personality, then identical twins reared apart should not be very similar to one another, or at least much less similar than they are to their adoptive family members. Any similarity between identical twins should be attributed to genetic factors (or chance).

The Relative Contribution of Genes

As discussed, the methods used by behavioral geneticists are extremely useful for disentangling the relative contribution of genes versus environment and provide a reliable method for addressing this complicated issue. In statistical terms, indicators of genetic infl uences are represented by the so-called heritabil- ity estimate (HE). The HE tells us how much of the variability between people’s personalities is accounted for by genes. For instance, if we fi nd that identical twins show no more resem- blance to each other than nonidentical twins, or if adopted chil- dren have no resemblance to their biological parents, then we would estimate the heritability to be .0. That is, 0% of the vari- ability in personality is accounted for by genes. If, on the other hand, identical twins were far more similar to each other than nonidentical twins, or if there was a high resemblance between

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adopted children and their biological parents, we would esti- mate the heritability to be closer to 1. That is, 100% of the vari- ability is accounted for by genes.

So, how heritable is personality? A good amount of research has been carried out to address this question. In a highly infl u- ential meta-analysis, Zuckerman (1991) concluded that there is a substantial hereditary aspect underlying most personality dimensions, and that environmental infl uences on personality traits are far less important than genetic ones. In his review of the literature, Zuckerman found some consistent results; corre- lations between identical twins are always higher than between nonidentical twins. Indeed, in most studies examined, the cor- relations for identical twins were at least twice as large as those for nonidentical twins. Several other reviews and infl uential studies have been carried out in the past decades, and fi ndings seem to show a consistent pattern; virtually every personality trait studied has a substantial heritability. Recent estimates of the heritability of personality traits suggest it ranges from .4 to .6 (Spinath & Johnson, 2011), that is, between 40% and 60% of the variability in personality is due to genetic factors (in case you were wondering, the heritability of intelligence ranges from .5 to .8). Given that a large portion of the variance will be accounted for by measurement error (because our measures are not perfect), the relative contribution of environmental fac- tors is at least somewhat smaller. Indeed, the genetic infl uences on personality have often been found to be quite substantial. The most compelling evidence derives from studies with identi- cal twins who grew up in completely different environments and had never met, but had almost identical vocational inter- ests, hobbies, and pets (Lykken, Bouchard, McGue, & Tellegen, 1993)! These studies are not abundant but they do remind us of the hidden power of genetics underlying many emblematic psychological traits.

At this point, we should note an important and sometimes overlooked point: HE is an estimate of the infl uence of genes on individual differences within a population. That is, it does not

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necessarily show the degree to which genes explain the charac- teristics of one specifi c person. For instance, although the HE of reading ability may be high, whether a person can read or not will also be infl uenced by whether he or she has been exposed to books and other reading material. Thus, heritability is a pop- ulation estimate and only implies a statistical propensity rather than an inescapable necessity to have a particular characteris- tic. Second, HEs are specifi c to time and place. That is, different HEs for the same personality trait could be found in different populations. For instance, when environmental infl uences on individuals in one population are very diverse and wide (such as in large cosmopolitan cities), the HE is likely to decrease. On the other hand, when conditions within an environment are homogenous (such as in small villages), the HE is likely to increase. Thus, HE should be seen as an estimate associated with variation in a population in a given study, rather than an explanation for one particular person’s behavior.

The Contribution of Environment

Although research on the heritability of personality has clearly demonstrated the importance of genes and biological factors underlying individual differences in personality differences, it has also illuminated the relative contribution of the environ- ment. Given that genes do not explain nearly as much as 100% of the variance in personality, the same studies provide evidence for the importance of the environment (although, as mentioned before, one cannot simply subtract the genetic variance from the total variance to obtain the estimate of the environmental infl uence, but rather needs to take into account error variance associated with measurement issues).

Before we outline the research on environmental infl uences, however, we should note that behavioral geneticists distinguish between two types of environment: shared environment and non- shared environment. Shared environment entails the aspects of the environment that are the same for people within a family.

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