Chapter 6 Genetics, Evolution, and Personality PDF

Chapter 6 Genetics, Evolution, and Personality Learning Objectives 6.1 Describe the procedures of twin studies and adoption studies 6.2 Identify some of the personality qualities that are genetically influenced 6.3 Identify two issues in behavioral genetics that complicate the process of drawing...

Chapter 6 Genetics, Evolution, and Personality Learning Objectives 6.1 Describe the procedures of twin studies and adoption studies 6.2 Identify some of the personality qualities that are genetically influenced 6.3 Identify two issues in behavioral genetics that complicate the process of drawing conclusions from findings 6.4 Examine the kind of work done in the field of molecular genetics and genomics 6.5 Examine four ways in which psychologists suggest that former evolutionary processes shaped present-day human behavior 6.6 Analyze how the assessment from the genetic viewpoint and the trait viewpoint differ 6.7 Outline two ways in which researchers have found evidence of genetic influence on problems in behavior 6.8 Identify two criticisms of using evolutionary ideas to understand personality Two newborns are lying in cradles behind the glass window of the hospital nursery. One lies peacefully for hours at a time, rarely crying and moving only a little. The other thrashes his arms and legs, screws up his face, and fills the air with piercing yowls. What could possibly make them so thoroughly different from each other so soon in life? A group of young men, 16 to 18 years old, have been hanging around the pool hall, acting cool, eyeing women who pass by, and trying to outdo one another with inventive insults. Occasionally, tempers flare, the lines of faces harden, and there's some pushing and taunting. This time, though, the taunting goes too far. A glint of dark steel, and the air is shattered by gunshots. Later, the dead one's grieving mother cries out, "Why do men do these things?" Part of who you are is the body you walk around in. Some people have big bodies, some have small ones. Some bodies are strong, some are frail. Some bodies are coordinated, some are klutzy. Some bodies turn toward dolls at a certain stage of life, others turn to Legos. Your body isn't your personality. But does it influence your personality? The idea that it does goes back at least to Hippocrates and Galen. As noted in Chapter 4, Hippocrates proposed four personality types. Galen added the idea that each reflects an excess of a bodily fluid. The idea that people's physical makeup determines their personalities has come up repeatedly ever since. The term physical makeup has meant different things at different times, however. In the early and mid-twentieth century, it meant physique or body build (see Box 6.1). Today, physical makeup means genes. Many people now believe that most qualities of personality are partly genetically determined. Box 6.1 Early Biological Views: Physique and Personality The idea that people's bodies relate to their personalities is reflected in popular stereotypes: the jolly fat man; the strong, adventurous hero; the frail intellectual. Is there any truth to it? The idea has had a long life. Kretschmer (1925) classified people as thin, muscular, or obese and found that each group was prone to a different set of disorders. W. H. ­Sheldon (1942) expanded the idea from categories to dimensions and looked at normal personality. He believed each quality relates to one of three layers of the embryo. For that reason, he named them after the layers: Endomorphy is the tendency toward plumpness ­(reflecting digestion). Endomorphs are soft and round. Mesomorphy is the tendency toward muscularity (reflecting predominance of bone and muscle). ­Mesomorphs are rectangular, hard, and strong. Ectomorphy is the tendency toward thinness (reflecting the skin and nervous system). Ectomorphs are delicate and frail, easily overwhelmed by stimulation. Most people have a little of each quality. In parallel with the physical dimensions, Sheldon proposed three aspects of temperament. Viscerotonia means qualities such as calmness, tolerance, sociability, love of comfort, and easygoingness. Somatotonia means qualities such as boldness, assertiveness, and a desire for adventure and activity. Cerebrotonia means avoidance of interaction, restraint, pain sensitivity, and a mental intensity approaching apprehensiveness. As he had predicted, Sheldon found that temperaments and somatotypes go together. Mesomorphy related to somatotonia, endomorphy to viscerotonia, and ectomorphy to cerebrotonia. Later studies also supported this view. These studies all said that body types relate to personality. But why? Does physique cause personality? Is the link more roundabout? The body types reflect well-known stereotypes, which include expectations about how people act. If we have such expectations, we may induce people to act as expected (Gacsaly & Borges, 1979). This can produce an association between physique and behavior. It would stem from social pressure, though, not body type per se. It's hard to know why associations exist between body type and personality. Partly because of this, many people were skeptical about the associations and interest in them gradually waned. Sheldon's ideas are no longer influential in personality psychology, but he stressed a theme that re-emerged only a couple of decades later. He believed that personality, along with body type, was inherited. He didn't test this belief. Indeed, in his time, it wasn't widely understood how to test it. Others found ways to do so, however, leading to the findings presented in the first half of this chapter. 6.1: Determining Genetic Influence on Personality 6.1 Describe the procedures of twin studies and adoption studies How do we decide whether a given personality quality is inherited? Family resemblance is one starting point, but it has a serious problem. Family members could be similar because of inheritance. But they also could be similar because they've learned to act in similar ways (see Chapter 10). To get a clearer picture required better methods. Psychologists turned to the discipline of genetics for ideas. The result was a mix of psychology and genetics called behavioral genetics. This is the study of genetic influences on behavioral qualities, including personality (Plomin, DeFries, Knopik, & Neiderhiser, 2013; Plomin & Rende, 1991). 6.1.1: Twin Study Method A method widely used in behavioral genetics is the twin study. It takes advantage of two reproductive events, which produce two types of twins. One kind of event occurs shortly after conception. A fertilized egg normally divides into two cells, then four, then eight, and eventually forms a person. Sometimes, though, the first two cells become separated, and each grows separately into a person. These persons are identical twins, or monozygotic (MZ) twins. Because they came from what was a single cell, they are 100% alike genetically. Comparisons between identical and fraternal twins can provide information about the heritability of characteristics. The second kind of event occurs in conception itself. Usually, only one egg is released from the mother's ovary, but occasionally two are. If both happen to be fertilized and develop simultaneously, the result is fraternal twins, or dizygotic (DZ) twins. Genetically, DZ twins are like any pair of brothers, pair of sisters, or brother and sister. They just happen to be born at the same time, rather than separately. As with any pair of siblings (brothers or sisters), DZ twins are, on average, 50% alike genetically (though specific pairs range from 0% to 100%). Interestingly enough, many twins are wrong about which kind they are, and errors are just as common for MZ as DZ twins. One study found that in about 30% of pairs, one twin was wrong, and in about 12% of pairs, both twins were wrong (Scarr & Carter-Saltzman, 1979). In a twin study examining some specific quality, a correlation is computed between sets of identical twins and their co-twins on that quality (see Figure 6.1). The same is done, separately, with pairs of same-sex fraternal twins. The two correlations are then compared. If identical twins are more similar to each other than fraternal twins, presumably it's because of the difference in degree of genetic similarity. Figure 6.1 A basic twin study method examines pairs of identical and same-sex fraternal twins raised together. Members of each twin pair are assessed on the variable of interest, and a separate correlation is computed for each type of twin. The correlation for fraternal (DZ) twins is subtracted from the correlation for identical (MZ) twins. ­Multiplying this difference by 2 gives an index of the heritability of the characteristic---an estimate of the proportion of variance in that characteristic that is accounted for by inheritance.  Figure 6.1 Full Alternative Text The index of genetic influence on a trait is termed a heritability estimate. This index represents the amount of variability in the population that's accounted for by inheritance in the trait under consideration. The higher the heritability, the stronger the evidence that genes matter. It's important to be careful here, because people sometimes read too much into this term. It does not represent the amount of a behavioral characteristic that's inherited by any one person. Nor does it explain why genes matter. The twin study method is based on the assumption that the degree of similarity of the life experiences of co-twins raised together is just as great for DZ pairs as for MZ pairs. This is critically important. You couldn't conclude that a difference between correlations comes from heredity if parents treated DZ twins differently from MZ twins. The difference in genetic overlap would be confounded with the difference in treatment. Are the two kinds of twin pairs treated more or less the same? The answer is a very cautious yes. MZ twins are more likely than DZ twins to be dressed alike, but the differences are slight (Plomin, DeFries, & McClearn, 1990). MZ twins also don't resemble each other morepersonality-wise if they were treated alike than if they were not (­Loehlin & Nichols, 1976). Even so, one study found that DZ twins who thought they were MZ twins were more alike than other DZ twins (Scarr & Carter-Saltzman, 1979). A later study found that MZ pairs recalled somewhat more similar experiences than DZ twin pairs, but these similarities didn't relate to personality similarity (Borkenau, ­Riemann, Angleitner, & Spinath, 2002). 6.1.2: Adoption Research Another way to study inheritance is an adoption study, which looks at how adopted children resemble the biological parents and the adoptive parents. Resemblance to biological parents is genetically based, whereas resemblance to adoptive parents is environmentally based. Another method combines features of the twin study with features of the adoption study. It's sometimes possible to study MZ twins who were adopted and raised separately. Because they grew up in different homes, environmental impacts should make them different, rather than similar. Similarity between these pairs can be contrasted with MZ twins raised together and DZ twins raised together. If heredity is important, then MZ twins---even if they were raised apart---should be more similar than DZ twins. If heredity is really important, then MZ twins raised apart should be nearly as similar as MZ twins raised together. 6.2: What Personality Qualities Are Genetically Influenced? 6.2 Identify some of the personality qualities that are genetically influenced Twin and adoption study methods have been used for more than five decades to study genetic effects on personality (Johnson, Vernon, & Feiler, 2008). Early work focused on temperaments. 6.2.1: Temperaments Arnold Buss and Robert Plomin (1984) used the term temperament to refer to an inherited personality trait present in early childhood. They looked for signs of possible temperaments in the behaviors of young children. Further work indicated to them that three dimensions of individual differences in personality deserve to be called temperaments: activity level, sociability, and emotionality.  Temperaments influence many kinds of behavior; for example, activity level expresses itself through the kinds of leisure activities people choose to engage in. Activity level is the person's output of energy or behavior. It has two highly correlated aspects: vigor (the intensity of behavior) and tempo (its speed). People high in activity level prefer high-intensity, fast-paced activities. Those lower in activity level take a more leisurely approach to things. Sociability is the tendency to prefer being with other people, rather than alone. It's a desire for sharing activities, along with the social responsiveness and stimulation that are part of interaction. Emotionality is the tendency to become emotionally aroused---easily and intensely---in upsetting situations. Early evidence that these temperaments are inherited came from twin studies in which parents rated their children (Buss & Plomin, 1975; Plomin, 1974; Plomin & Rowe, 1977). Correlations between parent ratings of activity, emotionality, and sociability were strong for MZ twins, and they were next to nonexistent for DZ twins. 6.2.2: More Recent Views of Temperaments Developmental researchers have become increasingly interested in temperaments over the past three decades, but they now view the nature of the temperaments a little differently. Mary Rothbart and her colleagues argue for approach and avoidance temperaments, which reflect tendencies to approach rewards and avoid threats, respectively (e.g., Derryberry & Rothbart, 1997; Rothbart, Ahadi, & Evans, 2000; Rothbart, Ahadi, Hershey, & Fisher, 2001; Rothbart & Bates, 1998; Rothbart, Ellis, Rueda, & Posner, 2003; Rothbart & Posner, 1985; see also Eisenberg, 2002; Eisenberg et al., 2004; Kochanska & Knaack, 2003; Nigg, 2000). The avoidance temperament, in some ways, resembles Buss and Plomin's (1984) emotionality. There also seems some resemblance between the approach temperament and sociability, though that one is less clear. The newer theorists also posit a third temperament that's generally termed effortful control. This temperament is about being focused and restrained. In part, it reflects attention management (persistence of attention during long tasks). It also reflects the ability to suppress approach when approach is situationally inappropriate. This temperament seems to imply a kind of planfulness versus impulsiveness. High levels of this temperament early in life relate to fewer problems with antisocial behavior later in life (Kochanska & Knaack, 2003). 6.2.3: Inheritance of Traits Early twin studies were done before trait theorists had begun to converge on the idea that personality has five basic factors (see Chapter 4). With the emergence of the five-factor model, work has increasingly focused on whether those five dimensions are genetically influenced (Bergeman et al., 1993; Heath, Neale, Kessler, Eaves, & Kendler, 1992; Jang, Livesley, & Vernon, 1996; Jang, McCrae, Angleitner, Riemann, & Livesley, 1998; Loehlin, 1992; Tellegen et al., 1988; Viken, Rose, Kaprio, & Koskenvuo, 1994). The answer is clearly yes. The effects are substantial and remarkably consistent across factors (Bouchard, 2004), although they decrease over the lifespan (Bleidorn, Kandler, & Caspi, 2014). Indeed, there's evidence of an invariant genetic influence on the five factors across cultures. Yamagata et al. (2006) concluded that the five factors may represent a common genetic heritage of the human species. Most twin studies of adult personality use self-reports or reports of people close to the twins. This approach has led to criticism of possible bias. To deal with this concern, Borkenau, Riemann, Angleitner, and Spinath (2001) conducted a twin study in which adult participants were videotaped and then rated by people who didn't know them. That study also found evidence of genetic influences on all five traits of the five-factor model. 6.2.4: Temperaments and the Five-Factor Model The supertraits that make up the five-factor model are broad and pervasive in influence. In that respect, they're a lot like temperaments. In fact, the five factors have considerable conceptual similarity to the temperaments described above (Caspi, Roberts, & Shiner, 2005; Digman & Shmelyov, 1996; Halverson, Kohnstamm, & Martin, 1994). One obvious similarity is that the temperament Buss and Plomin (1984) called emotionality and Rothbart and Posner (1985) called avoidance temperament very closely resembles neuroticism. Extraversion, from the "big five," also has overtones of an approach temperament. (Some people think extraversion is about approaching social rewards.) Extraversion suggests a preference for being with others, implying a possible link to sociability (Depue & Morrone-Strupinsky, 2005). Eysenck (1986) thought that activity was part of extraversion, suggesting that extraversion may blend sociability with activity. Another of the five factors---agreeableness---also has overtones of sociability, although again the two are not identical. Agreeableness suggests liking to be with people and enjoying social interaction. It goes beyond that, however, in having connotations of being easy to get along with. The trait of conscientiousness is a planful, persistent, focused orientation toward life's activities. Given the possibility that effortful control is a temperament (Pedersen, Plomin, McClearn, & Friberg, 1988; Rothbart et al., 2003), this would suggest another link between temperaments and the five-factor model. The last of the "big five" is openness to experience, or intellect. Recall from Chapter 4 that it's been hard to pin this trait down, so it has several labels. Some see links from this trait to intelligence. Intelligence is another quality that might be thought of as a temperament. It has the characteristics Buss and Plomin emphasized: It's genetically influenced (Bouchard, Lykken, McGue, Segal, & Tellegen, 1990; Plomin, 1989), and its effects on behavior are broad, manifest early in life, and continue throughout the life span. If we thought of intelligence as a temperament, the relationship between it and the fifth trait of the five-factor model would represent yet another link between temperament and trait models. In sum, although the fit isn't perfect, the set of qualities proposed as biologically based temperaments bears a strong resemblance to the qualities in the five-factor model. The places where the resemblance is less clear raise interesting questions. For example, why should activity and sociability be considered fundamental, rather than extraversion? Is extraversion really one trait, or two? As we said in Chapter 4, there are many ways to divide up the qualities of behavior, and it's sometimes hard to know which is best. 6.2.5: How Distinct Are the Genetics of Other Qualities? Evidence that genes influence behavior extends quite broadly. Many effects have emerged, some of which relate easily back to personality. For example, there's a genetic effect on risk of divorce (McGue & Lykken, 1992), which operates through personality (Jockin, McGue, & Lykken, 1996). There's a genetic effect on having adverse life events, which again appears to operate via personality (Saudino, Pedersen, Lichtenstein, McClearn, & Plomin, 1997). ­Heredity influences how much social support people have (Kessler, Kendler, Heath, Neale, & Eaves, 1992), which may reflect personality (Brissette, Scheier, & Carver, 2002; Kendler, 1997). People's attitudes on various topics are also genetically influenced (Eaves, Eysenck, & Martin, 1989; Olson, Vernon, Harris, & Jang, 2001; Tesser, 1993), which again may reflect personality. Findings such as these raise a question: To what extent are these various effects distinct and separate? The temperaments and supertraits discussed earlier are very broad. When evidence is found that some behavior is genetically influenced, one has to wonder whether this is a separate effect, or whether the effect is there because the behavior relates to a temperament or supertrait. For example, happiness has high heritability, but its heritability is fully accounted for by the heritability of neuroticism, extraversion, and conscientiousness (Weiss, Bates, & Luciano, 2008). The question of how many distinct qualities are separately influenced by inheritance hasn't been explored much. However, it's an important question. One study has explored it, within the framework of the five-factor model (Jang et al., 1998). This study found that not only were the five supertraits heritable, but so were most of the facet traits. Indeed, the genetic influences on facets were separate from the genetic influences on the overall traits. This suggests that many distinct qualities are genetically influenced, not just a few broad ones. It also calls into question the assumption that the superordinate traits derive from the facet characteristics. 6.2.6: Environmental Influences The twin studies that establish a powerful role for genetics in personality also show an important role for environmental factors. Surprisingly, however, the environment doesn't generally make twins alike. The environment seems to affect personality mostly by making twins different (Plomin & Daniels, 1987). This is called a nonshared environmental effect (Plomin & Daniels, 2011). What might be the sources of nonshared environmental influence? There isn't a lot of information on this. Several guesses sound reasonable, though (Dunn & Plomin, 1990; Rowe, 1994). For example, siblings often have different sets of friends, sometimes totally different, and peers have a big influence on kids. Having different friends may cause twins' personalities to diverge. If that happens, it's an environmental influence, but it's not shared by the twins. Another point is that siblings in families often develop roles that play off each other (e.g., Daniels, 1986; Hoffman, 1991). For example, if one child often helps another child with schoolwork, the two are developing styles of interacting that diverge. As another example, parents sometimes favor one child over another. This can affect the children's relationship, perhaps inducing differences between them. Again, the effects would be environmental, but they would differ from one child to the other. Questions still remain about these environment effects. For example, when behavior measures are used instead of rating scales, shared effects have been stronger (Turkheimer, 1998). For example, in the study in which videotaped behavior was rated by strangers, Borkenau et al. (2001) found a far larger shared environment effect than is typically found. Thus, variations in research methods may also influence what conclusions emerge. 6.3: Complications in Behavioral Genetics 6.3 Identify two issues in behavioral genetics that complicate the process of drawing conclusions from findings There are other complications, as well. We started this discussion with the idea that behavioral genetics methods give us heritability estimates. High heritability tells us that personality is genetically influenced. But things turn out to be more complicated than that. 6.3.1: Heritability Varies with the Environment Heritability is an estimate from a specific sample of data. That estimate may or may not be the same in another sample. The size of genetic and environmental influences depends partly on how much variability there is in each of them (Johnson, Turkheimer, Gottesman, & Bouchard, 2009). If either the population or the environment changes substantially, the heritability index can also change substantially. This point is illustrated by a study of genetic and environmental effects on a vocabulary IQ test (Rowe, Jacobson, & Van den Oord, 1999). As illustrated on the left side of Figure 6.2, among families in which the parents had little education, the shared environment had a large effect but genetics had no effect at all. On the right side of the figure, where parental education was very high, there was a huge genetic effect and no environmental effect. This sort of pattern means we have to be very cautious about generalizing estimates of heritability from one sample to the universe of people. Figure 6.2 Variability in vocabulary IQ accounted for by genetic factors and by shared environment factors, when examined as a function of ­parents' education level. Heritability is very low among children with poorly educated parents, but it is very high among children with highly educated parents Source: Adapted from Rowe et al., 1999. Figure 6.2 Full Alternative Text 6.3.2: Correlations between Genetic and Environmental Influences It is also increasingly recognized that genes and environment aren't just separate, unrelated things (Rutter, 2006). Oddly, there is often a correlation between a genetic influence and an environmental one. It was originally assumed that genetic and environmental influences are independent. But that turned out to be a naïve assumption. Dickens and Flynn (2001) illustrated this point using intelligence as an example. People with high intelligence (compared to people with less intelligence) gravitate to environments that foster learning. In those environments, they learn more. As a result, their IQs go up. The environment had the actual effect on their IQ. But the possibility for it to happen stemmed from their genetic makeup. Thus, the two influences are correlated. Why does this matter? It makes it very hard to sort out causal responsibility. Traditionally, the size of an environmental effect is judged by how much variability is left over---not explained by the genetic effect. If an environmental effect is mistaken to be a genetic effect (because they're correlated), the genetic effect gets the credit for what the environment is doing. Dickens and Flynn (2001) made this argument in the context of IQ, but it can easily be applied to personality. As we said in Chapter 4, people gravitate to environments that suit their interests---that let them be who they are. Maybe those environments even induce people to develop more of what first led them to go there. Someone who's slightly introverted who starts reading more may discover the joys of solitary pursuits and become even more introverted. Someone who's slightly extraverted who gets involved in group activities may discover he or she likes being in charge and develop greater extraversion. This issue arises any time a genetic factor makes it more likely that one person will enter an environment that's different from the environments other people enter. Sometimes, the impact comes from outsiders' genes, as when parents' genetic makeup leads them to create particular environments for their children. Sometimes, the impact comes when people's own genetic makeup influences what environments they seek out. Sometimes, it comes when people's genetic makeup affects the responses they induce from people around them. (As we said in Chapter 4, some people always bring a smile to your face, while others can make you frown just by entering the room.) 6.4: Molecular Genetics and Genomics 6.4 Examine the kind of work done in the field of molecular genetics and genomics As if things weren't already complicated enough, the world of research into genetic influences on behavior has changed radically in the past 15 years or so. The effort to map the human genome---the genetic blueprint of the body---was wildly successful. The "first draft" was completed in 2000, years ahead of schedule. The identification of gene sequences is becoming faster and less expensive all the time. It's increasingly possible to identify specific genes that influence differences among people---from vulnerability to disorders to normal personality qualities. Many believe the ability to identify genes linked to such differences will revolutionize medicine, psychiatry, and psychology (Plomin, 1995; Plomin & Crabbe, 2000; Plomin, DeFries, Craig, & McGuffin, 2003). A huge proportion of the human genome is identical for everyone. Interest focuses on the parts that vary. When different patterns of DNA (genetic material) can occur at a particular location, the different patterns are called alleles. The existence of a difference at that location is called a ­polymorphism. A genotype difference between persons means they have different alleles at some particular location. Whereas twin research is referred to as quantitative genetics, the attempt to relate differences in particular gene locations to other measurable differences among persons is called molecular genetics (Carey, 2003) or genomics. In the not too distant past, for most practical purposes genes were treated as abstractions, inferred from patterns of inheritance. Now, they are increasingly viewed as what they are: specific DNA sequences in specific locations of chromosomes (Cole, 2009). The question for personality is whether specific polymorphisms influence a given personality quality. The answer to this question isn't likely to be at all simple. It's very likely that many genes relate to any given personality quality (Plomin & Crabbe, 2000). Despite this, the first genomic studies on this topic used what's called a candidate gene strategy. This means that particular gene locations were examined selectively, based on evidence linking those genes to particular biological processes, as well as theoretical reasoning linking those biological processes to personality. Several genes have been identified that appear to have clear relevance to normal personality. An example is a gene called DRD4, which relates to receptors for dopamine in the brain. It has several alleles, one longer than the others. Two research teams found almost simultaneously that people with the long allele have high scores on personality scales that relate to novelty seeking (Benjamin, Patterson, Greenberg, Murphy, & Hamer, 1996; Ebstein et al., 1996). It has since been linked to risky decisions and difficulty delaying (Carpenter, Garcia, & Lum, 2011). Another candidate gene related to dopamine function, called DRD2 (now called ANKK1), has also been linked to personality measures of fun seeking (Reuter, Schmitz, Corr, & Hennig, 2006), impulsive responding to emotion (Carver, LeMoult, Johnson, & Joormann, 2014), and extraversion (Smillie, Cooper, & Pickering, 2011). These findings, along with those for DRD4, fit with the view that dopamine is involved in reward pursuit (a view that's discussed in Chapter 7). Another candidate gene relates to the use of serotonin in the brain. It's called the serotonin transporter gene, or 5HTTLPR. Several groups of researchers have found a link of the short allele of that gene to high scores on neuroticism and low scores on agreeableness (e.g., Greenberg et al., 2000; Lesch et al., 1996; Sen et al., 2004). Others have related it to impulsivity and aggressiveness (for review, see Carver, Johnson, & Joormann, 2008). The associations with neuroticism have been somewhat difficult to replicate. Evidence is beginning to accumulate that the 5HTTLPR polymorphism is more about impulse versus constraint than about neuroticism per se (Carver et al., 2008; Carver, Johnson, Joormann, Kim, & Nam, 2011). Single-gene discoveries can be very exciting. We repeat, though, that it's overwhelmingly likely that most genetic influences on behavior will involve small contributions from many genes (Plomin & Crabbe, 2000). Indeed, that may be one reason why single-gene discoveries have been hard to replicate. Even though the media continue to trumpet every new discovery as "the gene for" something or other, that's badly misleading (Kendler, 2005). Some researchers worry that candidate gene studies, in particular, are vulnerable to false positives. In part for that reason and in part because of the rapid advance of technology, other molecular geneticists argue that the candidate gene strategy should be abandoned. It's now possible to conduct genome-wide association studies (GWAS), in which the entire genome is examined for any and all differences that relate to an outcome of interest. Done properly, this kind of study involves a huge number of research participants (there are so many genes to test that the large number alone creates the potential for false positives). This kind of study is also very costly. Some believe, however, that this is the path of the future in behavioral genomics. Whether candidate gene studies continue or GWASs take their place, it's clear that the tools of molecular genomics radically change the nature of genetic research bearing on many topics, including personality. It's of some interest that this newer genetic approach (like the older one) doesn't really specify what aspects of personality matter. Rather, it provides tools for testing genetic contribution to whatever aspect of personality a researcher is interested in. 6.4.1: Gene-by-Environment Interactions A different kind of complication from the genomic approach comes from examination of interactions between genes and environment. The concept of interaction came up in Chapters 2 and 4. In Chapter 4, we talked about trait-by-situation interactions. We said there that a situation might cause one reaction in a person with one trait and a different reaction in a person with a different trait. The point here is the same, but substitute genetic makeup for trait. Geneticists long believed that gene-by-environment (GxE) interactions were rare (Rutter, 2006), but this is proving not to be true. A good many studies provide evidence of GxE interactions (see Rutter, 2006). Most of them have looked at how genetic factors interact with situations of life adversity or stress. Particularly common are studies examining consequences of childhood adversity. The typical strategy is to test whether early adversity affects people with one genotype differently than it affects people with a different genotype. Often it does (see Carver et al., 2014, for discussion of examples). How to test properly for such effects raises technical issues (Moffitt, Caspi, & Rutter, 2006), and there's a great deal of debate about the usefulness of research looking for them (Caspi, Hariri, Holmes, Uher, & Moffitt, 2010) and how to interpret them. For example, very positive environments sometimes have beneficial effects on the very genotype that is most affected by adversity. This has led to the argument that we should think of the genotype in terms of sensitivity to the environment rather than vulnerability (Belsky & Pluess, 2009; Pluess & Belsky, 2013). Given the large number of interactions that have emerged, the search for GxE effects is likely to remain an important part of the field in the future. 6.4.2: Environmental Effects on Gene Expression The idea of a GxE interaction is that genes render some people more susceptible than others to environmental influences. How does that happen? One possibility is that environments influence how genes act. Environments don't change the strands of DNA that make up the gene, but they do affect their ability to function. Gene expression is the term used when the gene engages in the processes that create a protein. Interestingly, gene expression is not the same throughout the body. Gene expression varies by region and type of cell involved (e.g., brain cells, blood cells). Gene expression is influenced by several factors that affect the gene's accessibility to other chemicals. One influence is called methylation: the attachment of methyl chemical groups to what's called the gene's promoter region (its "on" switch). When there's more methylation, there's less gene expression. This doesn't involve a change in the gene itself. For that reason, it's called an epigenetic effect (which in this context means "in addition to genetic"). Methylation can be affected by stress level and even by diet (Champagne & Mashoodh, 2009; Gilbert & Epel, 2009). There's growing evidence that gene expression can be affected by many kinds of variation in the environment (Cole, 2009, 2014; Gilbert & Epel, 2009; Rutter, 2006). Most of this evidence comes from research with laboratory animals, but more and more is being done with humans. Much of the human research thus far has involved genes implicated in stress responses. For example, chronic social isolation can greatly alter the expression of genes that are involved in immune responses (Cole, 2009). A particularly astonishing discovery from research into gene expression is that epigenetic changes (patterns of methylation) can be passed from one generation to the next, just as genetic influences are passed onward (Gilbert & Epel, 2009). Now, put that together in your mind with the fact that the epigenetic changes reflect experience with the environment. The inescapable conclusion is that changes that are caused by experience with the environment can be inherited by offspring (Champagne & Mashoodh, 2009)---an idea that would have prompted ridicule 40 years ago. The field of epigenetics introduces even greater complexity into the effort to separate the influences of genes from those of the environment. It is now clear that the environment can influence how the genes work, and the genes can influence how the environment works. We clearly cannot talk about just one or just the other. 6.5: Evolution and Human Behavior 6.5 Examine four ways in which psychologists suggest that former evolutionary processes shaped present-day human behavior We now change directions somewhat. Humans are all members of a species that evolved across millennia. The view that humans are a product of evolution leads to the possibility that ancient evolutionary processes have a major influence on present-day human behavior. This line of thought is tied to several labels, including sociobiology and evolutionary psychology (Barkow, Cosmides, & Tooby, 1992; Bjorklund & Pellegrini, 2002; Buss, 1991, 1995; Caporael, 2001; Heschl, 2002; Tooby & Cosmides, 1989, 1990). Work deriving from this group of ideas has grown rapidly in recent years. 6.5.1: Sociobiology and Evolutionary Psychology Sociobiology was proposed as the study of the biological basis of social behavior (Alexander, 1979; Barash, 1986, 2001; Crawford, 1989; Crawford, Smith, & Krebs, 1987; Dawkins, 1976; Lumsden & Wilson, 1981; Wilson, 1975). The core assumption was that many---perhaps all---forms of social interaction are products of evolution. That is, the patterns were retained genetically because at some point they conferred an adaptive advantage.  Evolutionary psychologists believe that even acts of altruism, such as volunteering for a rescue team, may have a genetic basis. Sociobiologists focused on the question of how behavior patterns might get built in (see also Box 6.2). Their work led in some surprising directions. For example, it led to a way to account for altruism, a tendency that seems very hard to explain in evolutionary terms. Altruism is acting for the welfare of others, to the point of sacrificing one's own well-being for someone else. Altruism would seem to confer a biological disadvantage. That is, being altruistic may help someone, but it also might get you killed. This would prevent your genes from being passed on to the next generation. If the genes aren't passed on, a genetically based tendency toward altruism should disappear very quickly. Box 6.2 Theoretical Issue: Universal Adaptations and Why There Are Individual Differences The basic concepts of natural selection and population genetics are simple. If a characteristic differs from person to person, it means that each gene contributing to that characteristic has several potential forms, or alleles. Selection means that one allele is more likely to show up in the next generation because it helped with survival or reproduction, or is less likely to show up because it interfered with survival or reproduction. This is directional selection: a shift toward a higher proportion of the adaptive allele in the population's next generation. If it goes on long enough, directional selection can even eliminate individual differences. Over many generations, those without the adaptive allele fail to reproduce, and a larger proportion of the next generation has the adaptive one. In principle, this is how a characteristic can become universal in the population. Many characteristics influence survival. For example, in a world where strength matters (which probably was true during human evolution), strength makes you more likely to survive long enough to reproduce. That sends genes for strength into the next generation. As long as these genes are well represented in the population, the population will tend to survive and create yet another generation. But wait. If some characteristics are more adaptive than others, why are there individual differences at all? Why aren't we all large and strong and smart and stealthy and whatever else is good to be? A tricky thing about selection is that whether a value is adaptive depends on the context. Sometimes, a value that's useful in one environment is not just ­useless---but even fatal---in another. For example, openness to experience is adaptive in a benign environment, but if there are lots of diseases around, it's adaptive not to be so open. Indeed, there's evidence that higher prevalence of disease in particular environments relates to lower level of openness among the population living there (Schaller & Murray, 2008). In the long run, genetic variability in the population is necessary for the population to survive in a world that changes. Thus, another kind of selection is important, termed stabilizing selection. It maintains genetic variability (­Plomin, 1981). Stabilizing selection occurs when an intermediate value of a characteristic is more adaptive than the value at either extreme. Presumably, intermediate values reflect combinations of alleles, rather than specific alleles, and probably involve multiple genes. Predominance of intermediate values thus implies genetic variability. How can an intermediate value of a characteristic be more adaptive than an extreme value? Here's an example. It's important for people to have some sociability, because humans are such a social species. Having too little sociability isn't adaptive. But neither is it adaptive to have too much sociability. A person with extremely high sociability can hardly bear to be alone, and life sometimes requires people to be alone. Intermediate values are especially adaptive in many of the domains that are relevant to personality. That's why personality traits vary from person to person: There's genetic diversity on those traits. Otherwise, there would be only a single personality, which everyone would have. However, the process of evolution isn't really entirely a matter of individual survival (Wilson & Wilson, 2008). What ultimately matters is a gene pool, in a population. If one group in a population survives, prospers, and reproduces at a high rate, its genes move onward into subsequent generations more than other groups' genes. This means there are ways to get your genes carried forward besides reproducing on your own. Your genes are helped into the next generation by anything that helps your part of the gene pool reproduce. This idea is called inclusive fitness (Hamilton, 1964). If you act altruistically for a relative, it helps the relative survive. If an extremely altruistic act (in which you die) saves a great many of your relatives, it helps aspects of your genetic makeup be passed on because your relatives resemble you genetically. This phenomenon is sometimes called kin selection. Thus, it's argued, a tendency to be altruistic may be genetically based. This implies that people will be more altruistic toward those in their kinship group than strangers (especially competitors). This seems to be true (Burnstein, Crandall, & Kitayama, 1994). Also fitting this view, there seems to be a genetic contribution to empathic concern for others, which may underlie altruism (Burnstein et al., 1994; Matthews, Batson, Horn, & Rosenman, 1981; Rushton, Fulker, Neale, Nias, & Eysenck, 1986). Indeed, emotional closeness, which increases with genetic relatedness, seems to underlie the effect of relatedness on altruism (Korchmaros & Kenny, 2001). This idea has been extended to suggest an evolutionary basis for cooperation even among nonrelatives. This idea in turn has been expanded even further by the argument that evolution has built into humans several different ways to regulate relationships. From an evolutionary view, the issue is whether such regulatory tendencies lead to better outcomes for the group. Because cooperation promotes better group outcomes, some conclude that a tendency to cooperate is part of human nature (Guisinger & Blatt, 1994; Kriegman & Knight, 1988; McCullough, 2008). But there's also evidence that punishing people who don't cooperate leads to better group outcomes (Fehr & Gächter, 2002). Maybe punishing people for such actions (taking revenge) is also genetically built into human nature (McCullough, Kurzban, & Tabak, 2013). Finally, even after people have transgressed and been punished, there may be important reasons to restore the damaged relationship. This suggests an evolutionary role for forgiveness (McCullough, Pedersen, Tabak, & Carter, 2014). Perhaps all of these human experiences are products of evolution. These are some of the themes of evolutionary psychology, the idea that human behavioral tendencies have a basis in evolution. 6.5.2: Genetic Similarity and Attraction The idea that people act altruistically toward relatives was extended by Rushton and his colleagues (Rushton, 1989a; Rushton, Russell, & Wells, 1984) to what they call genetic similarity theory. The core idea is what we've said already: A gene is represented in the next generation by anything that brings about reproduction of any organism in which copies of the gene exist. That may mean altruism to your kinship group, but Rushton says it means other things, as well. He argued that genetic similarity has an influence on who attracts you. Specifically, you're more attracted to strangers who resemble you genetically than those who don't. How does this help the survival of the gene? If you're attracted to someone, you may become sexually involved, which may result in offspring. Offspring have genes from both parents. By making you attracted to someone with genes like yours, your genes increase the odds that genes like themselves will be copied (from one parent or both) into a new person, thus passing into the next generation. Are people attracted to others whose genes resemble their own? Maybe. Rushton (1988) had couples take blood tests that give a rough index of genetic similarity. He found that sexually involved couples had in common 50% of the genetic markers. When he took the data and paired people randomly, the pairs shared only 43% of the ­markers--- significantly less. Rushton went on to compare couples who'd had children with those who hadn't. Those with children shared 52% of the genetic markers; those with no children shared only 44%. Thus, among sexually active couples, those who were most similar were also most likely to have reproduced. This attraction effect also applies to same-sex friendships. Rushton (1989b) repeated his study with pairs of men (all heterosexual) who were close friends. The pairs of friends shared 54% of the genetic markers, and the random pairs shared only 48%. Again, genetic similarity related to attraction. How do people detect genetic similarity in others? One possibility is that we are drawn to others who share our facial and body features. People who look like us seem like family and therefore attract us. Another possibility is that genetic similarity is conveyed by smell. Consistent with this, there's evidence that women prefer the odor of men who are genetically similar to their fathers (Jacob, McClintock, Zelano, & Ober, 2002). Outside your awareness, you may recognize those who resemble you by subtle physical cues. The general idea that people choose mates on the basis of particular characteristics is called assortative mating (Thiessen & Gregg, 1980). Mating definitely isn't random. People select their mates on the basis of a variety of characteristics. Often, the features that influence mate selection are similarities to the self (Buss, 1985; Rushton & Bons, 2005). 6.5.3: Avoidance of Incest Genetic similarity may be good up to a point. But too much similarity creates problems. If parents are very closely related to each other, it increases the chances that harmful recessive mutations will be expressed. The result can be poorer health and lower survival for the offspring (Ilmonen et al., 2008). The closer the parents' relationship, the greater the risk. Thus, animals of many species seem to have evolved mechanisms to avoid in breeding (Lieberman, Tooby, & Cosmides, 2007). In humans, this is often called an incest taboo. Biologically, it is most important that incest be avoided during periods of maximum fertility---ovulation---because it's conception that creates the problems. Consistent with this reasoning, women report greater disgust at the idea of incest during periods of high fertility than at other times (Fessler & Navarrete, 2004). In fact, there's evidence that college-age women avoid even verbal contact with their fathers during periods of high fertility (Lieberman, Pillsworth, & Haselton, 2011). This study used cell-phone records. During high fertility days, women called their fathers (but not their mothers) less often (Figure 6.3). If their fathers called them, they talked for shorter periods. Figure 6.3 Frequency with which college women called their mothers and their fathers during times of the month in which they were more fertile and less fertile. Women called their fathers less often (but not their ­mothers) when they were fertile than when they weren't. Source: Based on Lieberman et al., 2011. Figure 6.3 Full Alternative Text 6.5.4: Mate Selection and Competition for Mates We've talked at some length about the importance of getting genes to the next generation. (It was once said that a person is just a gene's way of creating another gene \[Barash, 2001\].) No surprise, then, that the evolutionary view on personality focuses closely on mating (Gangestad & Simpson, 2000). Indeed, from this view, mating is what life's all about (although other issues do arise when you think about the complexities of mating). Just as certain qualities confer survival advantage, certain qualities also confer reproductive advantage.  Both men and women are in competition for desirable mates. Mating involves competition. Males compete with one another; females compete with one another. But what's being competed for differs between the sexes. Trivers (1972) argued that males and females evolved different strategies, based on their roles in reproduction. Female humans have greater investment in offspring than males: They carry them for nine months, and they're more tied to caring for them after birth. The general rule in biology is that the sex with the greater investment can generate fewer offspring over the life span, because of the commitment of time and energy to each. The sex with greater investment thus is choosier about a mate. The sex with less investment can create more offspring and is less discriminating. Given the difference in biological investment, the strategy of women is to tend to hold back from mating until they identify the best available male. Best here is defined as quality of genetic contribution, parental care, and material support for the mate and offspring. In contrast, the strategy of males is to maximize sexual opportunities, copulating as often as possible. This also means seeking partners who are available and fertile (Buss, 1994a, 1994b). In this view, men tend to view women as sex objects, whereas women tend to view men as success objects. These differences in orientation should produce different strategies for trying to get the opportunity to mate. David Buss and David Schmitt (1993) examined differences in how men and women compete for and choose mates and how the strategies differ from short to long term (see also Buss, 1994a, 1994b; Feingold, 1992; Schmitt & Buss, 1996). If men are interested in finding fertile partners, women should compete by stressing attributes that relate to fertility---youth and beauty. If women want to find partners who will provide for them and their babies, men should compete by stressing their status, dominance and ambition, and wealth or potential for wealth (Sidanius, Pratto, & Bobo, 1994; Sprecher, Sullivan, & Hatfield, 1994). What do men and women actually do to compete for mates? College students report doing pretty much what we just described (Buss, 1988). Women enhance their beauty with makeup, jewelry, clothing, and hairstyles. They also play hard to get, to incite widespread interest among males. This permits women to be choosy once candidates have been identified (see also Kenrick, Sadalla, Groth, & Trost, 1990). Men, on the other hand, brag about their accomplishments and earning potential, display expensive possessions, and flex their muscles (Sundie et al., 2011). In fact, just seeing women around makes men do these things even more (Roney, 2003). Consistent with this picture, people selectively attend to signs of dominance among males and to signs of physical attractiveness among females (Maner, DeWall, & Gailliot, 2008). Buss (1989) examined mate preferences in 37 different cultures around the world. Cultural differences were relatively rare. The preferences of U.S. college students didn't differ much from those of people elsewhere. Males (more than females) were drawn to cues of reproductive capacity. Females (more than males) were drawn to cues indicating resources. The resource issue may not be a case of "more is better." It may just be that men who don't have an acceptable level of resources are out of the running (Kenrick, Sundie, Nicastle, & Stone, 2001). Females are also drawn to cues of dominance and high status (Cunningham, Barbee, & Pike, 1990; Feingold, 1992; Kenrick et al., 1990; Sadalla, Kendrick, & Vershure, 1987).Interestingly, when ovulating, women's desires for dominant and charming men can overwhelm their more rational judgments about reliability (Durante, Griskevicius, Simpson, Cantú, & Li, 2012). Despite these gender differences, the qualities just listed don't always rank high in people's lists of desired characteristics. This leads some people to be skeptical of their importance. But rankings can also be deceiving. Other research gave people tight "budgets" for getting what they want in a partner (Li, Bailey, Kenrick, & Linsenmeier, 2002). Given that they couldn't be choosy about everything, what did they go for first? In this situation, men saw attractiveness as a necessity rather than an option, women saw status and resources as necessities, and both saw kindness and intelligence as necessities. Researchers have studied implications of the evolutionary model in several ways. For example, research shows that men prefer younger women---especially as they grow older---consistent with the seeking of reproductive capacity. This comes from a study of the age ranges specified in singles' ads (Kenrick & Keefe, 1992). As illustrated in Figure 6.4, men past age 25 specified an age range that extended increasingly below their own age. Women, in contrast, tended to express a preference for men slightly older than themselves. Figure 6.4 Singles' ads placed by men and women often specify the age range of persons of the opposite sex whom the placer of the ad would like to meet. In this sample of ads, as men aged, they expressed an increasing preference for younger women. Women tended to prefer men slightly older than they were, and the extent of that preference didn't change over time. Source: Based on Kenrick & Keefe,1992.  Figure 6.4 Full Alternative Text Also consistent with predictions from the evolutionary model are results from several other studies of gender differences (see Table 6.1). Compared to women, men are more interested in casual sex (Bailey, Gaulin, Agyei, & Gladue, 1994; Buss & Schmitt, 1993; Clark & Hatfield, 1989; Oliver & Hyde, 1993), want more sexual variety (Schmitt, 2003), and are less selective in their criteria for one-night stands (­Kenrick, Groth, Trost, & Sadalla, 1993). Men also are more easily turned on by visual erotica than women are (Bailey et al., 1994). Men's commitment to their relationship is shaken by exposure to a very attractive woman, whereas women's commitment is shaken by exposure to a very dominant man (Kenrick, Neuberg, Zierk, & Krones, 1994). Men's confidence in their own value as a mate is shaken by exposure to a very dominant man (but not an attractive one), and women's confidence in their value as a mate is shaken by exposure to a very attractive woman (but not a dominant one) (Gutierres, Kenrick, & Partch, 1999). Men overinterpret women's smiles and touches as implying sexual interest, and women are overly conservative in judging men's commitment in relationships that are forming (Buss, 2001). Both men and women experience jealousy, but there may be a difference in what creates this emotion. In theory, it's evolutionarily important for men to be concerned about paternity. (They want to support their own children, not someone else's.) Thus, men should be especially jealous about sexual infidelity. In theory, women are most concerned about whether the man will continue to support her and her children. Thus, women should be jealous about a man's having emotional bonds with another woman, rather than sex per se. Data from some studies fit this view: Men in them were more disturbed by thoughts of sexual infidelity, and women were more disturbed by thoughts of emotional infidelity (Buss, Larsen, Westen, & Semmelroth, 1992; see also Bailey et al., 1994). This finding has been challenged, however, partly because asking the question differently erases the gender difference (DeSteno, Bartlett, Braverman, & Salovey, 2002; Harris, 2002, 2003). On the other hand, content analysis of a reality-TV program called Cheaters found a clear gender difference in what the wounded partner was most concerned about (Kuhle, 2011). Jealousy is partly about what your partner may have done, but it's partly about the presence of rivals. Again, there seems to be a gender difference in what matters. Men are more jealous when the potential rival is dominant than when he is physically attractive; women are more jealous when the rival is physically attractive (Dijkstra & Buunk, 1998). 6.5.5: Mate Retention and Other Issues The first challenge in mating is getting a mate. The next challenge is keeping the mate. Men and women both have the potential to stray, and other people sometimes try to make that happen (Schmitt, 2004; Schmitt & Buss, 2001). People use various tactics to prevent this (Buss & Shackelford, 1997). Some tactics are used by men and women alike, but others differ by gender. Those that differ look a lot like the differences in tactics men and women use to find a mate in the first place. For example, men report spending a lot of money and giving in to their mates' wishes. Women try to make themselves look extra attractive and let others know their mate is already taken. Use of retention tactics also relates predictably to other factors in the relationship, but differently for men and women. Men use their tactics more if they think their wife is physically attractive. Men also work harder at keeping a wife who is young---independent of the man's age and the length of the relationship. In contrast, women work harder at keeping a husband with a high income. They also make more efforts if their husband is striving for high status (independent of current income). Although mating strategies are the starting point for much of this research on gender differences, other researchers have applied the theme more broadly. (As noted earlier, issues involved in mating lead to several other complexities in life.) Several have suggested that evolutionary differences cause men and women to have very different styles---indeed different needs---in communication (e.g., Gray, 1992; Tannen, 1990). Men are seen as having an individualistic, dominance-oriented, problem-solving approach. Women are seen as having an inclusive, sharing, communal approach. It is also often said that these differences in goals and patterns of communication create a good deal of misunderstanding between men and women. We should note that our discussion has emphasized gender differences, not similarities. There are, of course, many similarities. Both genders are looking for partners who have a good sense of humor and a pleasing ­personality (­Feingold, 1992), who are agreeable and emotionally stable (Kenrick et al., 1993), intelligent (Li et al., 2002), and kind and loving (Buss, 1994b). Both also seem to prefer partners whose faces are symmetrical (Grammer & Thornhill, 1994). The way men and women look at each other goes far beyond seeing each other as sex objects and success objects (Buss, 1994b). Nevertheless, gender differences do also seem important. 6.5.6: Aggression and the Young Male Syndrome Competition for mating opportunities leads to a lot of male posturing. It's also been blamed for many problem aspects of young men's behavior, including risky driving (Nell, 2002). But it can also lead to more. When males face hard competition for scarce resources (females), the result sometime is confrontation and potentially serious violence (­Hilton, Harris, & Rice, 2000). This pattern has been referred to as the young male syndrome (Wilson & Daly, 1985). It's viewed as partly an effect of evolutionary pressures from long ago and partly a response to situations that elicit the pattern. That is, although the pattern of behavior may be coded in every man's genes, it's most likely to emerge when current situations predict reproductive failure. The worst case would be a single man who's unemployed and thus a poor candidate as a mate. In line with this analysis, there's clear evidence that homicide is primarily a male affair (Daly & Wilson, 1990). Figure 6.5 displays the homicide rates in Chicago during a 16-year period, omitting cases in which the person killed was a relative. Males are far more likely to kill one another than are females. It's also obvious that the prime ages for killing are the prime ages for mating. According to Daly and Wilson, these killings come largely from conflicts over "face" and status (see also Wilson & Daly, 1996). Trivial events escalate into violence, and someone is killed. Figure 6.5 Homicide rates for males and females killing nonrelatives of the same sex in Chicago during the period 1965--1981.  Figure 6.5 Full Alternative Text Why killing instead of a ritualized display of aggressiveness? No one knows for sure. It's certain that easy access to guns in the United States plays a role. When weapons aren't available, the same pressures are more likely to result in punching and shouting. Deadly violence certainly is possible without weapons, but weapons make it far more likely. We should point out explicitly that the theory underlying this area of study is very different from the ideas about aggression and human nature of a few decades ago. This view isn't that aggression is part of human nature, expressed indiscriminately. Rather, physical aggression is seen as largely a male phenomenon, which occurs specifically as a result of sexual selection pressures in the competition for mates (Buss, 2005). Recent laboratory results confirm that men become more aggressive when status is an issue, and that mating motives also matter more when men are around other men (Griskevicius et al., 2009). Our focus here is on violence by young men toward their genetic competitors. It's worth noting that genetic competition also may play a role in violence within families. In particular, children---especially very young children---are far more likely to be killed by stepparents than by genetic parents (Daly & Wilson, 1988, 1996). The overall frequency of this event is low; most parents don't kill children. Yet if it happens, a stepparent is far more likely to be guilty than a biological parent. As is true of the young male syndrome, this finding may reflect a deep-rooted desire to help one's own genes into the next generation instead of a competitor's genes. We noted earlier that part of mating is retaining one's mate. People have a variety of tactics for doing this. Most of them are quite benign. Some can even be viewed as efforts at solidifying the relationship to make it resistant to temptation. However, some tactics of mate retention are coercive. Some men are so concerned about losing their mates---or unknowingly supporting a rival's child---that they become quite controlling. Tactics to control the woman sometimes escalate to violence against her (Hilton et al., 2000; Wilson & Daly, 1996). Sometimes that violence is a warning: Don't stray! Sometimes the violence is murder, ending all possibility of straying (Buss, 2005). When killings occur within families, most of the victims are wives. Killing one's wife is not a very useful reproductive strategy. But more limited aggression may be a different matter. Among chimpanzees, males who are aggressive to their mates (intimidating them) have been found to father more offspring than males who do this less (Feldblum et al., 2014). 6.6: Assessment from the Genetic and Evolutionary Perspective 6.6 Analyze how the assessment from the genetic viewpoint and the trait viewpoint differ The genetic orientation to personality, discussed in the first part of this chapter, tends to approach assessment of personality in much the same way as the trait view. What it offers, primarily, is some further ideas about what traits to assess. As we said earlier, those who take this view on personality believe that certain temperaments are inherited as biological substrates of personality. These, then, are the qualities to assess. Given the rise in influence of molecular genetics, some researchers raise the possibility that gene assessment will eventually become a common way of assessing personality. Although it's far too soon to be sure, many people who are prominent in this area see this as unlikely (e.g., Plomin & Crabbe, 2000). They argue that personality traits are influenced by many, many genes, each exerting a small effect. It will be hard enough to identify those genes, never mind use them as convenient personality tests---at least, not any time soon. 6.7: Problems in Behavior, and Behavior Change, from the Genetic and Evolutionary Perspective 6.7 Outline two ways in which researchers have found evidence of genetic influence on problems in behavior The genetic approach has made a major contribution to the analysis of problems in behavior. Behavior geneticists have examined the possibility that several kinds of vulnerabilities to problems may be influenced by inheritance (see Box 6.3). Molecular genetics is also starting to weigh in, but with the same problem it has with respect to normal personality: that many genes are likely to be involved in any given problem, not just one or two. Box 6.3 Living in a Postgenomic World The human genome is mapped. Researchers today know more than ever about the makeup of the human body and the functions of some of our genes (Plomin et al., 2003). The technology behind these advances is continuing its rapid development, with no signs of slowing down. Mapping the human genome will surely yield benefits. Some disorders are caused by single genes. Knowing the map makes it easier to find those genes. This information can be used in genetic counseling. People can be warned if they carry a gene for a disorder they may pass on to a child. Another benefit is genetic therapies, which now exist for some disorders---for example, to correct defects in producing blood cells. Some say having the map of the genome and using it to identify genetic weaknesses will usher in a new era of preventive medicine, dramatically changing the way we deal with disease (Lewin, 1990). The mapping of the genome excites imaginations, but it also raises concerns (Buchanan, Brock, Daniels, & Wikler, 2000; Fukuyama, 2002; Lynn, 2001; Stock, 2002). Knowing what genes control behavior raises serious ethical issues. For example, a great deal of pressure will doubtlessly arise to modify genes to create specific characteristics in new children, creating so-called designer babies (Plomin & Crabbe, 2000; Stock, 2002). Should this happen? Who will decide what characteristics should be created? What happens to people whose genetic characteristics are viewed by society as inferior? Knowledge about disorders also raises ethical issues. Will there be discrimination against people with particular genetic profiles? What happens to the cost of medical insurance when it's possible to know who's susceptible to specific diseases? Will insurance even be available to people with susceptibilities? This isn't an idle question. Insurance policies have been cancelled for entire families because of genetic problems in specific family members (Stolberg, 1994). The issue is serious enough that a federal law was passed in 2009 banning use of genetic tests to set insurance rates or deny coverage. The same issue arises with respect to psychological disorders. If it's known that your genes predispose you to mania or antisocial behavior, will you be able to get a job? Will you be able to have insurance against the possibility of needing treatment? If it's known that certain genetic profiles are associated with criminal tendencies, how will people with those profiles be treated (Glenn & Raine, 2014)? In short, the project to map the genome holds out much promise, but it also raises very difficult issues that will have to be addressed. You may want to start thinking about them, because they're issues that are in your future---and the future of your children. 6.7.1: Schizophrenia and Bipolar Disorder For many years, research on the behavior genetics of problems focused mainly on schizophrenia and bipolar disorder. Most was on schizophrenia, which is characterized by disorientation, confusion, cognitive disturbances, and a separation from reality. A well-known early study of genetic influence on schizophrenia by Gottesman and Shields (1972) began by recruiting members of a twin pair who were admitted to a hospital with a diagnosis of schizophrenia. The researchers sought out each one's co-twin and evaluated the co-twin's status. The term concordance is used to describe similarity of diagnosis. A pair of twins is concordant if they were both diagnosed as schizophrenic. This study found ­concordance rates of 50% among identical twins and 9% among fraternal twins. It thus appears that inheritance plays a role in schizophrenia. Indeed, this conclusion ­follows from over a dozen studies similar to this one. It should be noted that the twin study data also indicate that life circumstances play a role in determining who shows schizophrenic symptoms openly (Plomin & Rende, 1991). Some people have the genetic susceptibility but don't develop the disorder. This interaction between a susceptibility and a suitable context to touch it off reflects a diathesis-stress view of disorder (a GxE interaction). This is a theme that recurs in studying genetics and disorder. Molecular genetic studies have also been done to try to isolate gene locations that relate to schizophrenia. Several locations have been suggested (Faraone, Taylor, & Tsuang, 2002; Owen, Williams, & O'Donovan, 2004; Straub et al., 2002). However, as with candidate gene studies of personality traits, findings from these studies are often very difficult to replicate (DeLisi et al., 2002). Thus, there remains great uncertainty about what genes are involved in schizophrenia. A second disorder that appears to be affected by heredity is bipolar disorder. Mania is characterized by episodes of frenetic, hyperactive, grandiose, and talkative behavior, accompanied by a rush of ideas. Often the manic pattern is accompanied by positive emotion, but anger is also common. The onset of this disorder is usually sudden. As with schizophrenia, twin studies reveal very strong evidence of genetic contribution (McGuffin et al., 2003). There has also been molecular genetic research on this problem. One study linked bipolar disorder to a specific dominant gene on chromosome 11 in a group of Amish families (Egeland, Gerhard, Pauls, Sussex, & Kidd, 1987). Two other studies, however, found no link from the disorder to that gene, so it can't be the only one responsible for the disorder (Detera-Wadleigh et al., 1987; Hodgkinson, Sherrington, Gurling, Marchbanks, & Reeders, 1987). Scientists continue to look for genetic markers of bipolar disorder using the techniques of molecular genetics (Badner & Gershon, 2002). It's clear that biology plays a major role in bipolar disorder. However, it's also clear that events in the environment are important to how the disorder is expressed. In this case, at least a little is known about what environmental influences matter. For example, lack of sleep makes people with the disorder especially vulnerable to manic episodes. So does experiencing success in attaining goals (Johnson, 2005; Johnson et al., 2000). Once again, at least in the short term, there is a GxE interaction. 6.7.2: Substance Use and Antisocial Behavior Another focus of research on the genetics of problems is substance abuse. Quite some time ago, Eysenck (1964b) found that MZ twins were more likely to share tendencies toward alcoholism than DZ twins. Similar findings, along with information about the metabolic processes that underlie the difference, were reported by Schuckit and Rayses (1979). A more recent finding has provided an interesting reflection of the interweaving of genetic and environmental influences. In a study by Dick and Rose (2002), genetic contributions increased from about one-third of the ­variance at age 16 to one-half the variance---in the same sample---at age 18. Recent research has also implicated a specific polymorphism in the craving for alcohol that some people experience after having a small amount (Hutchison, McGeary, Smolen, Bryan, & Swift, 2002). It turns out to be the long allele of the DRD4 gene that was described earlier in the chapter---the gene that relates to measures of reward seeking. That allele has also been linked to the creation of stronger social bonds while drinking alcohol (Creswell et al., 2012). It has also been linked to heroin addiction (Kotler et al., 1997; Li et al., 1997; Shao et al., 2006) and to attention deficit disorder (Wu, Xiao, Sun, Zou, & Zhu, 2012). Another dopamine-related gene, ANKK1, has also been linked to attention deficit disorder (Bobb, Castellanos, Addington, & Rapoport, 2006; Sery et al., 2006) and substance abuse (Munafò, Matheson, & Flint, 2007). Another fast-growing area of research concerns antisocial behavior. There is evidence that temperaments play a role inthis sort of problem, particularly the approach temperament (Honomichl & Donnellan, 2012). Long ago Eysenck (1964a) reported that there were higher concordance rates among MZ than among DZ twins on both childhood behavior problems and adult crime. Further research on adult criminality also tends to fit the picture of a genetic influence (DiLalla & Gottesman, 1991; Wilson & Herrnstein, 1985). Most observers now believe that there are clear and strong genetic influences on antisocial behavior (Baker, Jacobson, Raine, Lozano, & Bezdjian, 2007; Moffitt, 2005a, 2005b; Rhee & Waldman, 2002). Evidence implicating specific dopamine genes in this sort of behavior is also starting to accumulate (e.g., Bakermans-Kranenburg & van Ijzendoorn, 2006). In all of these kinds of problems, there also appears to be evidence of an interaction between predisposition and environment. Several of the effects described in the preceding paragraphs involved interactions. Moffitt (2005a, 2005b) reviewed research on antisocial behavior, looking specifically for GxE interactions. One of her conclusions was that we should not frame questions in terms of whether genes influence this disorder but rather who is at greatest risk for the disorder when placed in circumstances that elicit problem behavior. The search for GxE interactions will likely remain an important focus for studies of problems, including this one. 6.7.3: Evolution and Problems in Behavior A somewhat different view of certain behavior problems is suggested by evolutionary psychology. Barash (1986) argued that many difficulties in human life stem from the fact that two kinds of evolution influence people. There is biological evolution, a very slow process that occurs over millennia. There is also cultural evolution, which is much faster. Your experiences of life stem partly from what biological evolution shaped humans to be during prehistory and partly from the cultural circumstances in which you live. Barash (1986) pointed out that biological evolution prepared us to live in a world very different from the one we live in now. Cultural evolution has raced far ahead, and biological evolution can't keep up. Living in a world in which we don't quite fit biologically, we are conflicted and alienated. Barash's point is a general one---not specific to a particular disorder---but it's an interesting one: That is, problems emerge when behavioral tendencies that have been built in as part of human nature conflict with pressures that are built into contemporary culture. 6.7.4: How Much Behavior Change Is Possible? The genetic perspective raises a major question about therapeutic behavior change. Biologically based personality qualities---whether temperaments or not---are, by definition, firmly anchored in the person's constitutional functioning. How easy can it be to alter these aspects of personality in any major way, through whatever therapeutic processes are used? Psychotherapy may change the person to some extent. But how far against their biological nature can people be expected to bend? This is an important issue, about which little is known. It's been suggested that even true temperaments can be modified, within limits. But what are the limits? It seems likely that some kinds of change are more difficult to create and sustain for some people than for others. For example, it will be harder for a therapy aimed at reducing emotional reactions to be effective for someone high in emotionality than for someone lower in that temperament. In fact, there may be some people whose temperaments make some kinds of therapy so difficult as to be impractical. Nonetheless, it should also be recognized that the heritability of personality, though strong, is not complete. There's a good deal of influence from experiences. Thus, the data that establish a genetic influence on personality also show that genetic determination is not total. The extent to which genetic tendencies limit behavior change is an important issue. It's clear, however, that psychological processes matter, even for disorders that are strongly influenced by inheritance, such as bipolar disorder. Although medication is very important in the management of this disorder (see Chapter 7), psychological treatments of various kinds have also proven beneficial (Johnson & Leahy, 2003). 6.8: Problems and Prospects for the Genetic and Evolutionary Perspective 6.8 Identify two criticisms of using evolutionary ideas to understand personality The genetic perspective on personality has roots that go far back in history. Yet in many ways, today's views are quite new. Research makes a strong case that many aspects of personality have a genetic base, but complex issues still remain in understanding how genes interact with the environment to influence personality. With advances in molecular genetics, researchers are now trying to link particular genes with qualities of personality---an approach that's newer still. The ideas that form evolutionary personality psychology are also fairly recent. In considering the usefulness of these ideas in thinking about personality, several issues arise. For example, temperaments are broad tendencies reflected in fundamental aspects of behavior. The fact that temperaments are so basic, however, raises a question about how to view their role. Does it make more sense to think of temperaments as all of personality, as part of personality, or as the bedrock on which personality is constructed? Since many personality traits seem heritable and many of the traits relate conceptually to temperaments, perhaps we should view temperaments as the starting points from which the conceptually related traits emerge (Caspi et al., 2005). Here's another question: How many traits are genetically influenced, and how many just look heritable because they derive from the first group? Recent evidence suggests that facets of the five supertraits are separately heritable. This puts a different twist on the question. Maybe we should be asking whether temperaments are unitary, broad qualities that are just displayed in diverse ways or whether they instead are convenient aggregates of what are really separate traits. A final question concerns the fact that the genetic approach to personality intrinsically takes no position on how personality should be conceptualized or what aspects of personality matter. Rather, it provides tools for testing genetic contributions to diverse aspects of personality. Ultimately, the theoretical viewpoint being tested by the genetic research must be rooted somewhere else. One such place is trait psychology (see Chapter 4). Another is biological process model (see Chapter 7). Another aspect of the viewpoint discussed in this chapter is sociobiology and evolutionary psychology. This view on personality has been controversial during its relatively brief existence, and it has been criticized on several grounds (e.g., Miller, Putcha-Bhagavatula, & Pedersen, 2002). The early arguments were very theoretical and had little supporting evidence. Sociobiology was seen by some as a game of speculation, rather than a serious science. More than a few people scorned the ideas under discussion as unfalsifiable and indeed untestable. In the past couple of decades, however, this situation changed dramatically. As more precise ideas were developed about the implications of evolutionary theory, this way of thinking led to a surge of studies. Evolutionary psychology is now an area of vigorous research activity. It seems clear that evolutionary ideas provide a wealth of hypotheses for researchers. Moreover, the hypotheses are becoming more and more sophisticated. Nevertheless, there remains concern about whether the hypotheses being studied by these researchers really depend on evolutionary theory, as opposed to merely beingconsistent with it. Indeed, some recent critics argue that support for many key evolutionary hypotheses is highly ambiguous and does not support the conclusions drawn (Buller, 2005a, 2005b; Richardson, 2007). One challenge evolutionary psychology faces today is that of making clear predictions that resist alternative interpretations. This issue, of course, is faced by all views on personality. The issue, however, seems likely to remain an especially important one for this approach for some time. Evolutionary psychology has also been criticized because its statements sometimes have disturbing political and social overtones. Some regard arguments about how human nature evolved as thinly veiled justifications for unfair social conditions in today's world (see Kitcher, 1987, and the succeeding commentaries; Lewontin, Rose, & Kamin, 1984). That is, the ideas explain why men are bullies, why there's a double standard of sexual behavior for men and women, and why race and class differences exist. These explanations provide a basis for considering such conditions as natural, which is only a small step away from saying they should continue to exist (Pratto & Hegarty, 2000). Some people view these overtones of evolutionary thinking as racist and sexist, and some have shown considerable hostility toward the theories themselves. One response to this sort of criticism is to point out that evolution is a natural force that works dispassionately, based on the principles of reproduction and survival. In the arena of evolution, issues of equal rights and equal opportunities have no meaning. It may well be that in today's world, some of the results of evolution work against some people, because evolution prepared us to fit not this world but the world of prehistory. If people are disadvantaged by the consequences of evolution, it's something that must be dealt with by the cultures that people have built. The fact that the theory explains why inequity exists can't be used as an argument that the theory is wrong. As you might expect, though, this response isn't entirely satisfying to critics. Despite controversies such as these, there remains a huge interest in evolutionary ideas in today's personality psychology. These ideas will be an important part of the discussion of personality for years to come. Summary: Genetics, Evolution, and Personality The approach to personality rooted in inheritance and evolution has two facets. One emphasizes that your personality is tied to the biological body you inherit. This idea goes far back in history, but today's version of the idea is quite different, emphasizing the role of genes. Behavior genetics provides ways to find out whether personality differences are inherited. In twin studies, correlations among identical twins are compared with correlations among fraternal twins; in adoption studies, children are compared with their biological and adoptive families. Studies of identical twins raised apart provide yet a different look at the effects of inheritance and environment. Twin research has been used to look at genetic con­tributions to a variety of dispositions, starting with ­temperaments: broad, inherited traits that appear early in life. Early evidence supported genetic influences on activity level, emotionality, and sociability. Other views of temperaments have also been suggested, including temperaments for approach, avoidance, and effortful control. There's also evidence of genetic influence in the "big five" supertraits and other variables. It's unclear whether the "big five" derive from (or duplicate) the temperaments studied under other names. It's also unclear whether the influence of heredity on other variables depends on associations between the other variables and a temperament. Recent developments in molecular genetics provide a new tool in the search for genetic influences on personality. Now, there's evidence of specific genes playing roles in traits, including novelty seeking, neuroticism, and perhaps effortful control or impulsivity. This has been an active area of research in recent years. The idea that dispositions are genetically influenced can be extended to suggest that many aspects of human social behavior are products of evolution. This idea is behind an area of work termed sociobiology or evolutionary psychology. Sociobiologists propose ways to account for various aspects of human behavior---even behavior that, on the face of it, seems not to provide an evolutionary advantage. Altruism, for example, is understood as people acting for the benefit of their family groups, so that the family's genes are more likely to be continued (kin selection). This idea has been extended to the notion that people are attracted to other people who share their genetic makeup. The evolutionary view also has implications concerning mate selection, including the idea that males and females use different strategies. The male strategy is to mate whenever possible, and males are drawn to signs of reproductive capability. The female strategy is to seek the best male available, and females are drawn to signs of resources. People use the relevant strategies and act in ways that make them seem better candidates as mates. Mating pressures also may lead to aggression among young men. Theory suggests that violence is most likely among men of reproductive age who are in poor reproductive circumstances. Evidence seems to bear this out, along with the idea that much violence concerns conflicts over status. The genetic approach to personality says little about assessment except to suggest what dispositions are particularly important to assess---those that have biological links. Assessment directly from genes will not likely occur soon, due to the probable involvement of many genes in any given trait. With regard to problems in behavior, there is substantial evidence that schizophrenia and manic--depressive disorder are affected by heredity, as are tendencies toward substance abuse and antisocial behavior. Like other topics, the study of disorder is beginning to use the tools of molecular biology to search for genetic influences. With regard to therapeutic behavior change, this approach raises a question on the basis of studies of temperament: How much can people be expected to change, even with therapy, in directions that deviate from their biological makeup?