Biological Aspects Flashcards
What do you call research on the association between genes and behaviour
Research on ‘behavioural genomics’ which is the study of how genes affect behaviour and how the complex nature of genes function together and with the environment to influence behaviour
Define and describe temperament
Stable individual differences in emotional reactivity.
Basic aspects of temperament involves four dimensions:
- Activity: vigorous motion vs. passivity
- Emotionality: how easily aroused to anger or fear vs. calmness
- Sociability: how much you enjoy people and being around others
- Agressiveness/impulsivity
What are the goals of behavioural genetic research in personality (introduction)
- Determine the percentage of individual differences in a trait that can be attributed to genetic differences and the percentage that can be attributed to environmental differences
- Determine the ways in which genes and environment interact and correlate with each other to produce individual differences
- Determine precisely where in the “environment” environmental effects exist—e.g., parental socialization, different teachers to which children are exposed
Describe the research methods used in genetics & personality
– Univariate genetic analysis, the most basic and well known method in behavioral genetics, decomposes the vari- ance of a single variable (phenotypic variance) into the variance due to genetic differences between individuals and that due to the environment unique to each individual. This is done by comparing the similarity (e.g., measured by a correlation coefficient, r) of monozygotic (MZ) and dizygotic (DZ) twins on the measured variable.
- FAMILY STUDIES Correlates the degree of genetic overlap among family members with the degree of similarity in personality trait. If a trait is highly heritable, family members with greater genetic relatedness should be more similar to one another on the trait than family members who are less closely genetically related
- TWIN STUDIES are often the main source of data surrounding the inherited predispositions of personality traits. Estimates heritability by gauging whether identical (monozygotic or MZ) twins, who share 100 percent of genes, are more similar than fraternal (dizygotic or DZ) twins, who share only 50 percent of genes
If MZ twins are more similar than DZ twins, this provides evidence of heritability - Consequently, ADOPTION STUDIES are used to detangle genetic and environmental factors. Positive correlations on traits between adopted children and adoptive parents provide evidence of environmental influence. Positive correlations between adopted children and genetic parents provide evidence of genetic influence.
What are the overall main findings from behavioural genetic research in personality
- HERITABILITY OF PERSONALITY TRAITS
The variance in almost any psychological individual difference is at least partly attributable to genetic influences. The well-known heritability statistic, which represents the proportion of total variation in an observed trait (or phenotype) attributable to genes, is around 50% across numerous measures of normal personality
The rest of the variance in personality is accounted for by unique environmental influences, those experiences that we do not share with, and thus make us different from, family members. The shared family environment – those environments that make us similar to other family members – seems to have little significant influence on the variation in personality. The finding of 50% heritability of personality is robust, and holds across diverse assessments, including (i) self-reported broad superfactors (e.g., the ‘Big 5’; Bouchard & Loehlin, 2001); (ii) self- and peer-ratings of personality (Riemann, Angleitner, & Strelau, 1997); and (iii) observational measures of personality (Borkenau, Riemann, Angleitner, & Spinath, 2001).
– Summaries of behavioral genetic data yield heritability estimates for major personality traits (extraversion, agreeableness, conscientiousness, neuroticism, openness to experience) of about 20–45 percent (EYSENCK 1990)
– Linked to the Big Five trait neuroticism– the serotonin transporter gene or 5-HTTLPR, has the strongest evidence linking it to neuroticism and other anxiety-related traits, such as harm avoidance. – Even so, the gene appears to account for only about 1 to 2 percent of the variance for these traits (AZAR, 2002)
- SEXUAL ORIENTATION – the object of a person’s sexual desires, whether the person is attracted to those of the same sex or of a different sex - may be inherited
- - Bailey et al. (1993) – 30-70% heritability
- - Le Vay (1991) – differences in the hypothalamus
Describe findings from twin studies
- MINNESOTA TWIN STUDY (Bouchard, 1999):
In studying 350 pairs of twins, including pairs of identical and fraternal twins reared together and apart, researchers found that identical twins, whether raised together or apart, have very similar personalities. They found that these twins who share the same genetic makeup also often shared very similar personality traits - these similarities are greater than observed in fraternal twins who don’t have identical genetic makeup.
– Such as Jack/Oskar who were separated in infancy - one grew up in Germany and the other outside of Europe. They were found to share very similar habits such as being absentminded and having domineering/angry temperament
– For most of the traits measured, more than half the variation was found to be due to heredity, leaving less than half determined by the influence of parents, home environment and other experiences in life.
– No single gene is believed responsible for any one of these traits. Instead, each trait, the Minnesota researchers propose, is determined by a great number of genes in combination, so that the pattern of inheritance is complex and indirect.
– The Minnesota results lend weight and precision to earlier work that pointed to the importance of a child’s temperament in development. For instance, the New York Longitudinal Study, conducted by Thomas identified three basic temperaments in children, each of which could lead to behavioral problems if not handled well.
– Resultantly, for parents, the study points to the importance of treating each child in accord with his innate temperament. Lyken argues that a big mistake for parents is to treat all kids the same. To guide and shape a child you have to respect his individuality, adapt to it. - FOWLER+BAKER 2008 there is a genetic influence in even social behaviours and attitudes: they found that identical twins are more alike in whether they vote in elections than are fraternal twins. Suggesting there may a genetic basis for patterns in behaviour, however there is a lack of understanding of why such associations emerge.
- MCCARTNEY etal 1990 found that there is an inverse correlation between personality similarity and age for both MZ and DZ twins, thus as twins get older their personalities become more different. When moving from childhood to adulthood, the environmental effects on personality therefore become more evident.
- - This can been explained by non shared environmental variance where features of the environment that children who are raised in the same home experience differently. For example, RICH (1990) suggests that peers make a big difference on personality traits. So as the child grows older, some genetic predispositions become less important whilst others become more.
Evaluation of twin studies
- NOT CONCLUSIVE
Even with an attribution of 50% the explanation is not conclusive as there must be other contributory factors to the development of aggression. Indeed, the results found are perhaps not due to the twins shared genetic makeup but their shared environment. Also, MZ twins are identical in physical appearance and are thus more likely to be treated equally by those around them (Joseph, 2002). Therefore, within this study there is an interaction between nature and nurture, which consequently decreases the internal validity of the study as well as the usefulness of the genetic explanation, as the cause of the personality traits remains uncertain.
Multivariate genetic analyses that offer a window to whether items and/or facets of core personality domains show a common genetic basis: univariate analyses, the more common approach in this literature to date (e.g. Bouchard, 2004), while undoubtedly useful for answering certain other questions, cannot provide insight to the underlying architecture across multiple facets.
- BUT, SAME AGES advantage of involving pairs of individuals of iden- tical age, but the twin design has its own problems. Other heritability methods are disadvantaged as data is sometimes collected when subjects are at different ages. If personality traits are expressed differently at different ages (i.e., some personality traits may be age dependent for genetic or environmental rea- sons), then the parent-offspring data simply do not reflect the same phenomena as the twin data. The sibling data are not sub- ject to this problem to the same degree, and they do show a slightly higher correlation in some studies. (TELLEGAN, 1990)
- NOT FULLY IDENTICAL a major limitation of heritability studies involving twins is the idea that environment begins after they are born. However identical twins whilst sharing the same genetic makeup, SEGAL has reported that they can experience differences during prenatal development such as nutrition or due to different levels of blood flow that reaches to them.
- SAPOLSKY highlighted the role of hormones whereby stress hormones that a mother might experience may result in the feutus developing a smaller brain, particularly the region that is in charge of turning off stress hormones. Therefore, the individual will have more life time exposure to stress and a higher baseline level of stress. Known as non mendelian inheritance of traits (non genetic) Therefore as they are born they may still be to an extent different - SAPOLSKY: extremely small sample sizes in studies where MZ twins reared apart compared to DZ twins. Eg 44 in Minnesota. It makes the results extremely difficult to generalise to the wider population
- SAPOLSKY has argued that genetics appear to have an effect on developing personality traits such as introversion- extroversion but this effect is indirect. It was proposed that children early in life are treated differently depending on their physical appearance which is an extremely heritable feature. Thus it was found that those who were treated more favourably (more physically attractive) were more likely to show extroversion later in adulthood. So there is heritability of physical trait which mediates the development of personality traits.
Describe findings from adoption studies
- DANIELS+PLOMIN 1985: Studied why some infants are open and responsive to attention right away, some take time to open up, and still yet, some others are fearful and withdrawn. It is difficult to tell whether babies are shy because their mothers are shy and thus do not take them out very much, or because the shy mothers pass down their shyness traits. Measures of this study attempted to clarify the relationship between the infants and adoptive and biological parental shyness, parental sociability, and parental introversion-extraversion
Adoptive parents were given questionnaires that asked them to rate their infants’ shyness levels, and then to rate themselves on the traits listed previously. It must be noted that the self-reported ratings of the biological were performed before the birth of the infants, and the scoring of the infants’ shyness were performed by the adoptive parents when the babies were two years old. The results showed that in nonadoptive families, the parents who reported high rates of shyness, low rates of sociability, and high rates of introversion also had shy infants. This was also seen in adoptive families whose parents rated similarly, indicating that a combination of home environment and genetics must come into play.
One significant conclusion was made in this study that was based on the fact that biological mothers rated high in shyness, and their adopted-away babies were also shy. This strengthens the possibility of a genetic link overshadowing family environment.
Evaluation of adoption studies
- DETANGLER Adoption studies are powerful because they get around the equal environments assumption as they take out the shared environment element seen in twin studies—genetic and environmental causes are unconfounded.
- INCONCLUSIVE? However a myriad of questions remain unawnsered causing the genetic explanation of personality to remain inconclusive. For example, it is uncertain as to whether twins who were reared apart and show similar personalities were placed into similar types of homes or if they tried to act similarly when brought together as they knew they were twins.
- NOT REPRESENTATIVE One issue for adoption studies is that adoptees and their adoptive families might not be representative of the population as a whole, either because they have distinctive characteristics or because they span a narrower range. There is also the possibility that adopted children might be selectively placed with adoptive parents matched to the birth parents. These issues can be examined empirically. For example, in a longitudinal prospective adoption study of normal behavioural development that began in 1975, my colleagues and research has now moved on to other issues.
- NOT REALISTIC It may not be thought realistic to pursue adoption studies due to changes in the rates of adoption compared to earlier decades and challenges with regards to legislation. Adoption designs, how- ever, remain possible, as evidenced by the continued generation of new studies – for instance the Early Growth and Development Study (Leve, Neiderhiser, Scaramella, & Reiss, 2010). Incorporating these multiple methods into behavior genetic studies reduces the number of causal assumptions which need to be made, allows oth- ers to be tested, and increases the types of causal question that can be addressed by researchers (Plomin et al., 2008).
Describe genetics and personality change/stability
HOPPWOOD 2011: studied the genetic and environmental influences on personality stability and change during the transition to adulthood using three waves of personality trait data using a sample of twins assessed in late adolescence (approximately age 17), emerging adulthood (approximately age 24), and young adulthood (approximately age 29).
Although there was evidence for genetic contributions to stability and change in personality, these results provide support for the lifespan perspective given that non-shared environmental factors accounted for personality changes over time (Bleidorn et al., 2009). Genetic factors tended to influence trait levels overall, as well as the stability of those levels, but the non-shared environment was an important influence on changes in trait levels over time
HOWEVER.. NOT SEEN IN ALL TRAITS
Most twin and adoption studies of general intelligence demonstrate increasing genetic influence across the life span (from 20% in infancy to 60% in adulthood), in conjunction with non-shared environmental experiences (30%) (McClearn et al., 1997). It has been suggested that this occurs because small genetic effects in childhood become amplified during development. Furthermore, shared environmental effects (influences increasing similarity among family members) on intelligence, while modest in childhood, decrease to near zero by adolescence (Mackintosh, 1998).
- longitudinal twin design that make it particularly suited for the study of personality development in adulthood. First, the longitudinal twin design allows researchers to examine the genetic and environmental underpinnings of personality stability and change in pairs of genetically related adults of exactly the same age.
VIKEN. (1994) were one of the first who examined the degree of genetic and environmental rank-order stability within a longitudinal twin design. Specifically, using self-report data from nearly 15 000 adult Finnish twins, they estimated the genetic and environmental correlations for neuroticism and extraversion over a 6-year period in seven age cohorts ranging from 18 to 53 years at baseline.
These studies have established strong evidence for a highly stable genetic foundation of individual differences in broad personality traits in adulthood. However, this finding has often been misinterpreted to suggest that genes exclusively account for personality stability whereas change—if there is any—is mainly due to nonshared environmental influences.
It becomes apparent that the basic interpretation of ‘stable genetic vs. changing environmental influences’ is too simplistic. In other words, many behavioural genetic studies did not separate nonshared environmental variance from error variance, which is by definition uncorrelated over time. As a consequence, these studies may have underestimated the stability of nonshared environmental differences in personality over time.
Three general conclusions can be drawn from the aforementioned reviewed studies. First, there is a strong and relatively stable genetic foundation of individual differences in personality throughout the adult life span. Second, nonshared environmental variance in personality traits becomes more important and increasingly stable from early to middle adulthood. And third, depending on the length of the time interval, the age period, and the particular personality trait of interest, both genetic and environmental influences contribute to stability of and change in personality traits
Describe genetics and personality change/stability
HOPPWOOD 2011: studied the genetic and environmental influences on personality stability and change during the transition to adulthood using three waves of personality trait data using a sample of twins assessed in late adolescence (approximately age 17), emerging adulthood (approximately age 24), and young adulthood (approximately age 29).
Although there was evidence for genetic contributions to stability and change in personality, these results provide support for the lifespan perspective given that non-shared environmental factors accounted for personality changes over time (Bleidorn et al., 2009). Genetic factors tended to influence trait levels overall, as well as the stability of those levels, but the non-shared environment was an important influence on changes in trait levels over time
HOWEVER.. NOT SEEN IN ALL TRAITS
Most twin and adoption studies of general intelligence demonstrate increasing genetic influence across the life span (from 20% in infancy to 60% in adulthood), in conjunction with non-shared environmental experiences (30%) (McClearn et al., 1997). It has been suggested that this occurs because small genetic effects in childhood become amplified during development. Furthermore, shared environmental effects (influences increasing similarity among family members) on intelligence, while modest in childhood, decrease to near zero by adolescence (Mackintosh, 1998).
Describe studies showing a gene x environment interaction
This idea, that a specific genotype will only lead to a certain phenotype under the right environmental circumstances (or that a genotype can be moderated by the environment), is an example of ‘gene–environment interaction’.
- AGE One such example of behavior genetics elucidating effects of the environment is the finding that between-family effects (i.e., differ- ences in shared environment) typically decline sharply with increas- ing age (Rowe, 1994). In other words, rather than the effects of exposure to parents, social status, and neighborhoods cementing and amplifying their effects, instead they appear to diminish over time.
- MEDIATING ENVIRONMENTAL INFLUENCES While identical twins may have some similar personality traits, however, they still have distinct personalities, suggesting that genetics are not the only factor in determining personality.
HEATH (1998) divided a sample of female Australian twins into pairs concordant for a marriage-like partnership, concordant for no relationship, and discordant. The heritability of depression increased from 29% in married twins to 51% in unmarried twins over 31 years of age. Marriage, therefore, acted as a protective factor by reducing the genetic liability to depressive symptoms.
Ozkaragoz and Noble described a good example of gene–environment interaction. They showed that children of alcoholic parent(s) scored significantly higher on extraversion if carrying specific DRD2 genotypes
Describe research on the genetics of homosexuality
Has been suggested to be biologically based as many homosexuals report that they were attracted to members of the same sex before having any sexual experiences.
Current evidence suggests that genes provide modest and indirect influence (via childhood gender nonconformity) on adult sexual orientation.
- LANGSTROM etal 2010 found that homosexuality tends to run in families and that MZ twins are more likely than DZ twins to have the same sexual preference. Thus suggesting a genetic predisposition to homosexuality.
- - However, it is not completely genetic in origin - as 100% concordance rates are not found, there is the implication that the environment has an effect on sexual orientation. - BAILEY 2000: recruited twins systematically from the Australian Twin Registry and assessed their sexual orientation and 2 related traits: childhood gender nonconformity and continuous gender identity. Multivariate analyses showed that familial factors were important causes in the covariation among the three traits, and provided some support for genetic factors.
In a recent review the lowest concordances for single-sex MZ samples were 47% and 48%, for men and women, respectively (Bailey & Pillard, 1995).
In contrast, our MZ concordances were 20% and 24%, respectively, for the strict criterion that is most similar to those used in prior studies. This suggests that concordances from prior studies were inflated because of concordance-dependent ascertainment bias (Kendler & Eaves, 1989).
How can we understand the environment using genetics
An example of the use of genetic research to help us understand the environment has been called ‘the nature of nurture’ (PLOMIN, 1994).
Twin and adoption studies have shown that genetic factors can have effects on the environment itself and that such effects can be found on aspects of the environment measured in psychological research. Such effects, known as ‘genotype–environment correlations’, could operate in various ways. Genetic factors could affect the reactions we evoke in others and the experiences that we select, construct and re-construct in memory.
For example, autistic children evoke distancing responses in others and select non-social experiences that reinforce their genetic tendency towards social and communication abnormalities. Environmental influences need to be examined in genetically sensitive designs, and genetic influences need to be examined in environmentally sensitive designs that incorporate specific measures of the environment (Rutter et al., 1997).
Briefly describe the complexity of genes and personality
It is important to remember that genes are not solely responsible for our personality. Personality is a complex trait. A complex trait is a trait that is influenced by many different genetic and environmental factors.
Personality traits are also polygenic. This means that multiple genes are involved in determining a trait. In other words, there is no one ‘personality gene.’ These two factors make the study of genetic personality traits extremely complicated. Because personality is a complex trait, most researchers recognize that the genetic portion of our personality cannot be completely separated from environmental influences.
