Chapter 9: The Inheritance of Personality
behavior genetics and twins
4 When a trait or behavior is influenced by genes, then the trait and behavioral scores of identical (MZ) twins ought to be more highly correlated than the scores of fraternal (DZ) twins. By the same logic, closer relatives (siblings) ought to be more similar on a gene-influenced, inherited trait than more distant relatives (cousins).
genome-wide association studies
A large-scale analysis of the genomes of many people having a certain phenotype or disease, with the aim of finding genetic markers that correlate with that phenotype or disease.
agression & altruism
A tendencyto be aggressive can help a person to protectterritory, property, and mates, and also lead to dominance in the social group and higher status. But the same tendency can produce fighting, murder, and the industrial-scale murder called war.
asians vs cauasians 5-htt gene
Asian cultures emphasize cooperation and avoiding conflict over the kind of individualistic striv- ing said to be characteristic of Western cultures because of the emotional sensitivity associated with this allele, Asians might tend to find interpersonal conflict more aversive than do Westerners, and so make extra efforts to smooth it over
depression
Depression that follows a social loss—such as a breakup with a boyfriend or girlfriend, or bereavement—is characterized by pain, crying, and seeking social support. Depression that follows failure—such as flunking an exam or being fired from a job—is more often characterized by fatigue, pessimism, shame, and guilt. these reactions may have promoted survival. Pain signals that something has gone wrong and must be fixed.
Adaptation
Diversity is what makes adaptation to changing conditions possible. At the level of the species, a trait that used to be maladaptive or just irrelevant can suddenly become vital for survival. A trait that is adaptive in one situation may be harmful in another. The Big Five personality trait of neuroticism can cause needless anxiety in safe situations, but might promote lifesaving worry in dangerous ones.
biological reductionism
Everything about the mind can be reduced to biology Biological approaches to psychology, by themselves, tell us much more about biology than about psychology.
Sociosexuality, Agreeableness, and the Accuracy of Perception of Mate Value
Figure 9.4
accounting for individual differences
First, behavioral patterns evolve as reactions to particular envi- ronmental experiences. Only under certain conditions does the evolved tendency come "on line," sort of like the way the skin of a Caucasian has a biological ten- dency to darken if but only if it is exposed to the sun. people may have evolved several possible behavioral strategies, but ac- tually use the one that makes the most sense given their other characteristics. some biologically influenced behaviors may be frequency dependent, meaning that they adjust according to how common they are in the population at large. For example, one theory of psychopathy—a behavioral style of deception, de- ceit, and exploitation—is that it is biologically influenced in only a small number of people (Mealey, 1995). If more than a few individuals tried to live this way, nobody would ever believe anybody, and the psychopathic strategy for getting ahead would become evolutionarily impossible to maintain.
evolutionary theorists response to criticism
For any theoretical pro- posal in science—not just those in evolutionary psychology—alternative explanations are always possible. Moreover, whole, complex theories are seldom judged on the basis of one crucial, decisive study. Instead, numerous studies test bits and pieces as methods become available. Complex evolutionary theories of behavior are difficult to prove or disprove in their entirety, and some alternative explanations may never be ruled out, but empirical research can address specific predictions. the evolutionary theory of sex differences not only predicts that males should prefer mates younger than themselves and females should prefer mates who are older, but that this should be true in all cultures This finding does not prove that the reproductive motives described by evolutionary theory cause the age differences, nor does it rule out all possible al- ternative explanations; but in fairness it must be considered encouraging empirical support.
stress tests for evolutionary psychology: methodology
How can such evolutionary speculations be put to empirical test? What sort of experiment could we do to test the sexy son hypothesis, or to see whether men re- ally seek multiple sexual partners in order to maximize their genetic propagation? t is unwise to assume that every genetically influenced trait or behavior pattern exists because it has an adaptive advantage.
slow life history
Long time to sexual maturity Long life spans Low numbers of offspring High parental investment
biological determinism
Many behavioral phenomena might be the result not of evolutionary history but of humans responding to changing circumstances, especially social structure. The difference comes not from a specific innate module, but from a reasonable and flexible response to the biological and social facts of life According to the evolutionary view, the differences between men and women in mate selection and other behaviors are built-in through biological evolution. This view implies that it might be almost impossible to change these differences; at best, any change will occur at the speed of evolution, thus likely requiring thou- sands of years. his difference reverses the traditional sex roles and, from an evolutionary perspective, may counteract biology as well. How flexible will men and women turn out to be in the face of changing social circumstances? Time will tell.
human similarities
More than 99 percent of all human genes are identical from one person to the next. MZ twins are effectively the same in all of these varying genes; DZ twins share about half of them, on average, as is also the case for parents and offspring. , the statement that a mother shares 50 percent of her genetic material with her child really means that she shares 50 percent of the material that varies across individuals.
What heritability tells you: genes matter
Not all of personality comes from experience; some of it comes from genes.
why he estimates of heritability garnered from non-twin studies are about 20 percent, or half the average heritability estimated from twin studies?
One likely explanation is that the effects of genes are interactive and multiplicative rather than additive. That is, estimates of heritability based on twin studies assume that individual genes and the environment act independently to influence personality, and these influences can simply be added up. If that were true, then because DZ twins share (on average) half of the variable genes that MZ twins do, we could assume they are half as similar in gene expression. But things aren't so simple. As will be described later in the chapter, genes often operate dif- ferently depending on the other genes that are present. Moreover, genes will ex- press themselves in different ways in different environments and even members of the same family may grow up and live in different social contexts. As a result, while heritability estimates based on twins may be too high, those based on broader family relationships may be too low.
active person-environment transaction
People tend to select and even create environments that are compatible with and may magnify their ge- netically influenced tendencies. A person who inherits a predisposition toward sensation seeking may take dangerous drugs.
fast life history
Short time to sexual maturity Short life spans High numbers of offspring Little parental investment
molecular genetics
The dopaminergic systems of the brain (the parts of the brain influenced by dopamine) also play broad roles in the control and regulation of behavior and even bodily movement
evolution & behavior
The evolutionary approach to personality assumes that human behavioral patterns developed because they were helpful or necessary for survival in the evolutionary history of the species. The more a behavioral tendency helps an individual to survive and reproduce, the more likely the tendency will be to appear in subsequent generations.
gene-environment interaction
The genotype only provides the design, andso affects the behavioral phenotype indirectly, by influencing biological structure and physiology as they develop within an environment The environment can even affect heritability itself. Well-fed children will grow near the maximum of their genetic potential while poorly fed children will grow closer to their genetic minimum, and the height of the parents will not matter so much; the heritability coefficient for height will be much closer to 0.
reproductive instinct
The idea that people tend to want many offspring is not valid. There are individual differences. Theorists argue that the instinct need not be conscious. lthough you might or might not wantchildren, it cannot be denied that you would not behere unless somebody (your ancestors) had children. (Neither sterility nor absti- nence runs in anyone's family.) The same tendencies (e.g., sexual urges) that caused them to produce offspring are also present in you. Thus, your sexual urges are based on a reproductive instinct, whether or not you are consciously aware of it or wish to reproduce. It is also the case that your sexual urges do increase your chances of reproducing, whether you want them to or not, since birth control methods some- times fail. According to evolutionary theory, people have tendencies toward sexual behaviors in general because of the effects of similar sexual behaviors on past gen- erations' reproductive outcomes—not necessarily because of any current intention to propagate.
reactive person-environment transaction
The most basic way in which genes and environments interact is that the same environments that promote good outcomes for some people can promote bad outcomes for others, and vice versa
Borkenau implications
The result was that "extraversion was the only trait that seemed not to be influenced by shared environment. Every other trait measured in the study was affected by the shared environment. 1.The first is that the widely advertised conclusion that shared family en- vironment is unimportant for personality development was reached too quickly, on the basis of limited data. For many years, behavioral genetics research was based almost exclusively on self-report personality questionnaires, and these S data show little similarity across siblings raised together. But when personality is assessed by directly observing behavior, the picture looks different 2.Personality research can em- ploy many kinds of data, and they all should be used. Conclusions based on only one kind are at risk; consistent results across several kinds of data are more likely to hold up in the long run.
inclusive fitness
The total effect an individual has on proliferating its genes by producing its own offspring and by providing aid that enables other close relatives to increase the production of their offspring.
sexy son hypothesis
This hypothesis proposes that a few women consistently—and many women occasionally—follow an atypical reproductive strategy. Instead of maximizing the reproductive viability of their offspring by mating with a stable (but perhaps unexciting) male, they instead take their chances with an unstable but attractive one.
A model of sources of neuroticism
This trait can interact with specific experiences to create phobias or other vulnerabilities that may, over time, lead to mental illness. Notice that although biological vulnerability is an important factor, it does not lead to either neuroticism or mental illness unless the person also has negative experiences in his or her environment.
sociosexuality
Those who are more "re- stricted"—who score lower—are more interested in partners' personal qualities and their potential to be good parents women understand exactly what these high-sociosexuality men are up to. They know that someone who flashes wealth in a dating context is more likely to be interested in a short-term fling than a long-term relationship.
genes and relatability
To the degree that a trait is influenced by genes, people who are closer genetic relatives ought to be more similar on that trait than people who are more distantly related.
women and sexual partners
Women report more interest in having sex with someone other than their primary partner when the "other man" is significantly more attractive than their regular partner and they are themselves near ovulation (Pillsworth & Haselton, 2006). Moreover, women's short-term sexual partners tend to be more muscular than men with whom they have longer-term relationships (though it turns out to be important that they not be too muscular; Frederick & Haselton, 2007). But male attractiveness is more than just a matter of muscles: Women in their fertile period also find creative men espe- cially attractive (Haselton & Miller, 2006). It might be in order to attract these at- tractive, muscular, creative men that women tend to dress more provocatively when they are in the middle of their cycle
biological contributions of gender
a man's biological contribution to reproduction is relatively minimal Women bear and nurse children, so their youth and physical health are essential.
evolutionary psychology
addresses how patterns of behavior that characterize all humans may have originated in the survival value these characteristics provided over the history of the species. Two people with the same genes might have very different attributes, depending on the environments in which they are raised, and, as recent research is beginning to show, environments can actually shape how and even whether genes are expressed
behavioral genetics
addresses how traits are passed from parent to child and shared by biological relatives examines how personality traits are shared among biological relatives, including recent studies seeking to uncover the molecular genetic basis of personality.
5-HTT gene
associated with a serotonin transporter protein, has two variants, or alleles. They are called "short" and "long" based on their chromosomal structure. Several studies have shown that people with the short allele score higher on measures of neuroticism, a broad person- ality trait that (as we saw in Chapter 6) is relevant to anxiety and overreaction to stress This gene also appears to regulate the degree to which the amygdala and the prefrontal cortex work together, which may offer an important clue to the brain structure of depression prevalence of the short allele of the 5-HTT gene may vary across cultural groups. In particular, the allele appears to be present in about 75 percent of Japanese people, more than double its frequency in Caucasians
what another way to estimate heritability
calculate similarities in personality across relatives other than twins
Monozygotic
developed from a single fertilized ovum, as identical twins
why are twins are simple and elegant?
easy because MZ twins share on average twice as many variable genes as do DZ twins. However, these studies are not the only way to estimate heritability. Other kinds of relatives also vary in the degree to which they share genes. children share 50 per- cent of their variable genes with each of their biological parents, whereas adopted children (presumably) share no more of their personality-relevant genes with their adoptive parents than they would with any other person chosen at random. Full siblings also share, on average, 50 percent of the genes that vary, whereas half-siblings (who have one parent in common) share only 25 percent, and first cousins 12.5 percent
individual differences in evolution
evolution requires individual differences. Species change only through the selective propagation of the genes of the most successful individuals in earlier generations, which simply cannot happen if everybody is the same. So not only is it fair to expect a "theory of everything" like evolutionary psychology to explain individual differences, such an explanation is essential for the theory to work.
self-esteem
feelings of self-esteem evolved to monitor the degree to which a person is accepted by others. Humans are a highly social species, and few things are worse than being shunned by the community.
what does behavioral genetics
focuses exclusively on individual differences. Inheritance of species-specific traits that all humans share is the focus of evolutionary biology, which is discussed in the second half of this chapter.
heritability quotient
for twins:: Heritability quotient = (rMZ rDZ ) (that is, twice the difference between the correlation among MZ twins and the correlation among DZ twins). Across many, many traits, the average correlation across MZ twins is about .60, and across DZ twins it is about .40, when adjusted for age and gender This means that, according to twin studies, the average heritability of many traits is about .40, which is interpreted to mean that 40 percent of phenotypic (behav- ioral) variance is accounted for by genetic variance.
evocation person-environment transaction
girl who inherits a genetically based tendency to be easily angered may tend to create and thereby experience hostile social situations, a process parallel to the evocative person-environment transaction introduced Genes may even affect how a child is treated by his parents, which can be seen as an extreme example of an evocative person-situation transaction At the genetic level, one recent meta-analysis that surveyed 32 studies of twins concluded that boys with genetic tendencies toward poor self-control received less attention from their mothers
epigenetics
has begun to document how experience, especially early in life, can determine how or even whether a gene is expressed during development indicates that the experience of social stress can activate expression of genes that lead to vulnerabilities to de- pression, inflammatory diseases, and viral infections (The bottom line is that transactions between genes and the environment can go in both directions and can reinforce or counteract each other)-->genes can change environments and, as we are beginning to discover, environments can change genes
why are these numbers averages
he statistic that full siblings share 50 percent of the variable genes is a theoret- ical average of all siblings, and does not necessarily describe the similarity between any particular pair of brothers and sisters. It is possible, though highly unlikely, that two full siblings could share none of the variable genes at all his point underlines the fact that behavioral genetic analyses and the statistics they produce refer to groups or populations, not individuals when research concludes that a personality trait is, say, 50 percent heritable, this does not mean that half of the extent to which an individ- ual expresses that trait is determined genetically. Instead, it means that 50 percent of the degree to which the trait varies across the population can be attributed to genetic variation.
Nature versus nurture
heritability calculations do not solve the nature-nurture puzzle. Ever since scientists realized that heredity affects behavior, they have longed for a simple calculation that would indicate what percentage of any given trait was due to nature (heredity) and what percentage was due to nurture (upbringing and environment). Because heritability is the proportion of variation due to genetic influences, if there is no variation, then the heritability must approach zero. Heritability statistics are not the nature-nurture ratio; a biologically determined trait can have a zero heritability.
how genes affect personality
heritability statistics are not really very informative about the process by which genes affect personality and behavior. Anything affected by personality will also be affected, indirectly, by genes. But heritability analyses, by themselves, cannot tell us just how.
mating strategies
how individuals handle heterosexual relationships
DRD4
is also associated with the risk for attention deficit hyperactivity disorder (ADHD), which makes sense given the association between dopamine and brain regulation of cognition and behavior, as well as the related personality trait of impulsivity DRD4 apparently has nothing to do with risky behavior among skiers and snowboarders Moreover, sensation seeking is also relevant to serotonin and its related genes
heritability coefficient
is computed to reflect the degree to which variance of the trait in the populations can be attributed to variance in genes
evolutionarily man vs woman
man's greatest worry—especially for a man who has decided to stay with one woman and support her family—is that he might not be the biological father of the children he supports. This fact makes sex- ual infidelity by his mate his greatest danger and her greatest betrayal, from a bi- ological point of view. For a woman, however, the greatest danger is that her mate will develop an emotional bond with some other woman and so withdraw support— or, almost as bad, that her mate will share their family's resources with some other woman and her children. This makes emotional infidelity a greater threat than mere sexual infidelity, from the woman's biological point of view.
fast LH strategy
may have worked better for reproductive success, but in modern times, in most environments, the slow-LH strategy seems to be more effective. But individuals of both kinds still ex- ist, and may even appear to a different extent in different environments. Safe, pre- dictable environments promote the appearance of slow-LH individuals who marry late, have few children, and put extensive resources into raising them. Dangerous, unpredictable environments are more likely to produce fast-LH individuals who have children when they are very young but—especially if they are male—may not stay around to help support and raise them. Most current writing on LH tends to describe the slow-LH history as better overall, but there are tradeoffs. In one study, slow-LH individuals were observed to display behavior described as considerate, kind, hardworking, and reliable, but also socially awkward, insecure, and overcon- trolling (Sherman, Figueredo, & Funder, 2013). For their part, fast-LH individu- als came across as unpredictable, hostile, manipulative, and impulsive, but also as talkative, socially skilled, dominant, and charming. From an evolutionary perspec- tive, neither LH strategy is "better"; each is adapted to a different set of environ- mental circumstances.
Dark Triad
men are characterized narcissism, psychopathy, and Machiavellianism men appear to be prone to certain kinds of wishful thinking in which they are quick to conclude that women are sexually interested in them, even when they are not Relationship maintenance might also be the reason that both men and women who are in steady dating relationships find opposite-sex strangers less attractive than do those who are not in such relationships
attraction
men are more likely than women to place higher value on physical attractiveness. women are more likely to value economic security in their potential mates. heterosexual men are likely to desire (and typically do find) mates several years younger than themselves (the average age difference is about three years, and increases as men get older), whereas women prefer mates who are some- what older than themselves. Men are more likely to describe themselves as financially secure than as physically attractive, whereas women are more likely to describe their physical charms than their financial ones
heritability tells you: Insight into effects of the environment
non-genetic effects; specifically, how the early environment does—or does not—operate in shaping personality development. The research just cited did not specify which aspects of a child's environment are important The only exception was attention deficit hyperactivity disorder (ADHD), for which the shared family environment did not seem to matter. To some extent, results vary depending on the methods used
Behavioral genetics controversy: eugenics/cloning/fixed expectations
the belief that humanity could (and should) be improved through selective breeding. the belief that it might be technologically possible to produce a complete duplicate—psychological as well as physical—of a human being research on genetic bases of behavior might lead the public to think that outcomes such as intelligence, poverty, criminality, mental illness, and obesity are fixed in one's genes rather than changeable by experience or social circumstances ***first not really feasible
mate selection
the process by which people choose each other for sexual or romantic relationships
conservative bias
the tendency of analysts to downplay evidence of historical change and to reject evidence of challenges to traditional social patterns The basic assumption that our personalities have been selected over the millennia to favor behaviors that promote our individual survival may itself come from the larger culture
dizygotic twins
twins who are produced when two separate ova are fertilized by two separate sperm at roughly the same time
human flexibility
volutionary accounts seem to describe a lot of specific behavior as genetically programmed into the brain, whereas a general lesson of psychology is that humans are extraordinarily flexible creatures with a minimum of instinctive behavior patterns, com- pared with other species. , the issue is whether, in the domain of behavior, people evolved general capacities for planning and responding to the environment, or specific behavioral patterns What is the human evolutionary heritage? Is it a collection of specific responses triggered almost automatically by particular circumstances? Or is it the ability to plan, fore- see, choose, and even override instinctive tendencies?
COMT
was recently found to be associated with higher levels of dopamine in the prefrontal cortex and also with extraversion and reasoning ability This find- ing is especially exciting because it suggests a connection between a gene, a neurotransmitter, a personality trait, and an important aspect of intelligence.
