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The Developmental Behavior Genetic Perspective

My Take

Many researchers have found that IQ is highly heritable, with genetic effects accounting for approximately 50% of phenotype variance. It has also been discovered that as individuals age, the contribution of genetic factors to IQ increases while the contribution made by shared environmental effects decreases. Why do you think this might be the case? Do you think genetic effects can primarily explain differences in IQ? Is this representative of all cultures?

  • Large sample size
  • Results representative of preschool aged children
  • Interesting that influential effects differ depending on sex
  • Greater sex-typed behavior in children with older siblings of the same sex perhaps from modeling

The authors provide a logical explanation for their finding that shared environmental effects on gender role behavior are greater for boys than for girls. They believe this is probably the case, because boys experience stronger socialization influences (parents are more likely to stop a boy from playing with dolls than stop a girl from playing with trucks) and are more likely to think that others consider cross-gender typed play to be "bad." Do you agree with these explanations? Why or why not? Can you think of any other potential reasons for this finding?

  • Use experiments to test potential confounds of adoption and twin studies
  • Genes have powerful effects on many aspects of our lives (even our attitudes) > important to study genetic influence to understand ourselves and our world
  • "A human species whose members did not vary genetically with respect to significant cognitive and motivational attributes, and who were uniformly average by current standards, would have created a very different society than the one we know." -Bouchard et al. (1990)

Iervolino, Hines, Golombok, Rust, & Plomin, 2005

  • Parents completed the Preschool Activities Inventory (PSAI)
  • Environment and genetics differ in the extent to which these areas affect gender role behavior in boys and girls
  • For boys: moderate genetic and large shared environmental influence
  • For girls: large genetic and moderate shared environmental influence

People have raised the concern that information obtained from adoption studies is not generalizable to the human population, because the homes in which adopted people are raised may be quite similar to each other due to adoption practices. Not taking this homogenous environment into account may lead to an underestimation of shared environmental effects. Do you agree with this argument? If so, what is an appropriate way to account for this issue? In what ways would this change the findings that have been made based on adoption studies?

My Take

Plomin (2009)

The researchers discuss the prenatal testosterone exposure hypothesis, in which female twins with male co-twins are exposed to greater amounts of testosterone in the womb than female twins with female co-twins. Testosterone diffuses across the amniotic membrane, and is believed to alter female twins' with male co-twins later behaviors. For example, research has found that female twins with male co-twins score higher in sensation seeking, a behavior that is considered to be more typical of males. Scores on the PSAI have also been found to correlate with prenatal testosterone exposure in girls. Keeping these results in mind, what is your take on the prenatal testosterone exposure hypothesis? Do you think prenatal exposure to testosterone accounts for within-sex variation?

3 Types of GE Correlation:

My Take

Bouchard & McGue, 2003

Iervolino, Hines, Golombok, Rust, & Plomin, 2005

  • Organized three-step plan
  • Logical to think these effects have a significant impact on development
  • Exciting and challenging next step: detect environmental aspects that are specifically responsible for nonshared environmental effects like identifying genes responsible for heritability

Plomin (2009) explains that the Genotype-Environment theory has numerous implications. One of these involves a change from thinking about passive models of ways in which the environment influences people to models that acknowledge the active role individuals have in choosing, altering, and constructing their environments. How do you think we can use this theory and empirical research inspired by it to tackle issues prevalent in society today? What are additional implications of the theory?

  • Important implications of this theory and the research it inspires
  • Children-of-twins method makes studying unique genetic relationships possible
  • General cognitive factor (g) has been found to be a biological variable
  • The heritability of g increases during development, but may decline later in life
  • Genetic influence on personality trait variance is between 40 and 55%
  • Social attitudes have moderate to strong heritability
  • Religious affiliation is strongly influenced by environmental effects
  • Psychological interests are separate from personality, but are also influenced by genes
  • Concordance rates for many behavioral disorders are higher for MZ twins than DZ twins
  • 1. Passive: when children passively inherit family environments that are associated with their genetic propensities
  • 2. Evocative: when people evoke reactions from others on the basis of their genetic propensities
  • 3. Active: when people choose, alter, construct, or reconstruct experiences that are associated with their genetic propensities
  • Several studies testing the theory of GE effects have investigated 265 environmental variables, and found an average heritability of .27
  • If measures of the environment are heritable, we should be able to detect variation in DNA sequences causing this heritable variation
  • Plomin and his colleagues found DNA markers correlated with reading and g

Bouchard & McGue, 2003

  • Investigated genetic and environmental influences on gender role behavior
  • 3,990 3- to 4-year old twin and non-twin sibling pairs
  • Compared MZ and DZ twins, and younger siblings of twins to compare twin-specific shared environments and environments shared by all siblings

Plomin, Asbury, & Dunn, 2001

  • The standard behavioral genetic method involves separating the variance in a quantitative phenotype into genetic effects, shared environmental effects, and nonshared environmental effects using best-fit models to determine correlations
  • Adoption method used to divide genetic and environmental influences, but has limitations
  • Twin methods used, some claim twins are not representative of all populations because growing up as a twin is very different
  • More than one child/family needs to be studied to examine nonshared environmental effects
  • 1. Record differential experiences (measures unique to each child)
  • 2. Record the relation between differential experiences and differential outcomes
  • 3. Examine the extent to which relationships are causal
  • The Nonshared Environment and Adolescent Development project: attempted to address these steps

Plomin et al. (2001) acknowledge that nonshared environmental factors might differ with age. Do you agree? How might the effects of nonshared environmental factors change from age to age? How might these effects differ in different cultures?

Plomin (2009)

Plomin, Asbury, & Dunn, 2001

When referring to Scarr and McCartney's Genotype-Environment theory, Plomin (2009) discusses the three types of genotype-environment correlations (passive, evocative, and active). Which of these genotype-environment correlations do you think most significantly contributes to an individual's development? Why? Can you think of any other potential GE correlations that contribute to development?

  • What may seem to be an effect of the environment can be mediated by genetic factors
  • Scarr & McCartney: "We stress the role of the genotype in determining which environments are actually experienced and what effects they have on the developing person."

Further research is needed to explain nonshared environmental effects. What do you think is the best way to study the effects of nonshared environmental factors? Do you believe this is an area worth studying? Why or why not?

Goldhaber (2000)

Many developmental behavior geneticists believe in "good-enough parents" who are good enough to guarantee enough variability in the population to sustain reproductive viability and thus survival of the species. Efforts that go above and beyond or people who act as "superparents" are viewed as unnecessary and non-influential. Do you think there is such a thing as "good-enough parents?" Is it possible that there is a threshold at which a parent's job is efficient/inefficient?

  • Research has shown that children growing up in the same family have different effective environmental influences
  • Plomin et al. (2001) states that when it comes to psychological development, "environment makes siblings no more similar to one another than to children picked at random from the general population."
  • Effective environments are not shared = nonshared environment
  • Examples: family composition, sibling interactions, peer influences, and nonsystematic factors like accidents
  • Includes subjective perceptions > "a shared experience could have nonshared effects" (Plomin et al. (2001))

Iervolino et al., 2002

Tucker-Drob, Rhemtulla, Harden, Turkheimer, & Fask, 2011

  • Used adoptive and nonadoptive sibling data from the Colorado Adoption Project (CAP) and twin and sibling data from the Nonshared Environment and Adolescent Development Study (NEAD)
  • Final sample size: 395 families
  • Self-reports of peer-group preference assessed peer college orientation, peer delinquency, and peer popularity
  • Levels of genetic relatedness examined to separate genetic and environmental influences for peer preference
  • Used maximum likelihood model-fitting analyses to approximate the contribution of genetic (A), shared environment (C), and nonshared environment (E) factors
  • Environment plays a major role in the expression of genetic variance in cognitive ability during child development
  • SES correlates with parents' ability to provide high-quality educational resources
  • Unknown when Gene x SES effects start
  • Hypotheses:
  • 1. SES will positively correlate with developmental gains in mental ability
  • 2. Genes will affect change in mental ability (heritability will be greater at 2 than at 10 months)
  • 3. SES will moderate the genetic contribution to change in mental ability (increasing heritability will be greatest for children in high-SES families)
  • History of the nature/nurture debate:
  • John Locke (nurture) vs. Jean-Jacques Rousseau (nature)
  • Darwin and Mendel: part of heredity passes from generation to generation
  • Eugenics Movement (nature) vs. Watson's behaviorism (nurture)
  • Debate moved to studying how nature and nurture work together
  • Recent resurgence: 1) determine the ability of large social intervention projects to better the lives of those in need, 2) discoveries being made in molecular genetics and developmental biology, and 3) determine role of genetics and environment in defining psychological characteristics

Davis et al. (2009) provide a few explanations for their findings. Why do you think the heritability of general cognitive ability increases throughout development? Do you think the same results would emerge throughout adolescence, adulthood, and older adulthood?

Iervolino et al., 2002

Scarr and Plomin both discuss changes in the heredity/environment ratio across the life span. For example, Scarr states that the effects of the active gene-environment, which refers to people choosing environments where they feel comfortable, increases in importance over the life span. Passive gene-environmental effects, in which parents provide rearing environments associated with the genotype of the child, are believed to occur predominantly in the early years and decrease throughout development. What do you think about these life span differences? Do you agree with Scarr's ideas? How do you think the heredity/environment ratio changes across the life span?

Iervolino, Pike, Manke, Reiss, Hetherington, & Plomin, 2002

  • Genetic factors contributed to adolescents' choice of college-oriented peers
  • Environmental effects accounted for variance in peer delinquency in NEAD sample, genetic effects accounted for this in CAP sample
  • Genetic factors inconsistent for peer popularity
  • Nonshared environmental factors and measurement error explained variance for peer delinquency and popularity
  • Peer-group associations=major source of sibling differentiation during adolescence

My Take

Some people believe that infancy plays only a minor role in determining later cognitive ability. Others take the opposite stance, believing that infancy is a crucial time period for determining adult cognitive performance. For example, Heckman states that "at current levels of funding, we overinvest in most schooling and post-schooling programs and underinvest in preschool programs for disadvantaged persons." Do you agree or disagree with this statement? Do you believe infancy plays a significant role in determining adult cognitive performance? Why or why not?

The researchers found that the heritability of general cognitive ability increases over the life span. Besides g, what are other abilities for which you think the heritability increases over the life span? Why? What are some implications of these findings?

  • Interesting that heritability of g increases throughout development
  • Researchers think this may be due to the fact that when children begin school in middle childhood the variability of the daily environment encountered by twin pairs decreases > reduces importance of shared environment for developing cognition
  • Makes sense, would be interesting to do in other countries with different schooling practices

My Take

Goldhaber (2000)

  • Hypothesis: Individual differences in the characteristics of adolescents' peer groups would mainly be due to genetic differences between people
  • Research has shown that children actively select friends who are similar to them > likely genetic factors affect this process
  • Multiple measures of SES and used a diverse sample > results are more valid and generalizable
  • Valuable information with useful implications

Tucker-Drob et al., 2011

My Take

Basic Assumptions of a Developmental

Behavior Genetic Perspective:

  • Low statistical power, sample size may not have been large enough to detect a significant effect
  • Could reduce the generalizability of their findings
  • Contradict prior research, could compare power levels
  • Genetic and nonshared environmental factors shape peer selection and influence
  • Method and theory are independent
  • All measurable phenomena have one or more causes, each acting independently
  • Study behavior by partitioning variance
  • Believe genes are the relevant explanation of variability
  • "Nature develops via nurture" -Rowe (1994)

My Take

  • Used longitudinal data on 750 pairs of infant twins-tested at 10 months and 2 years
  • They found support for all of their hypotheses
  • Children from lower-SES families usually have less opportunities to participate with environments that nurture cognitive development > suppresses genetic influences on mental ability
  • Interesting that two of the most prominent researchers of this area believe genes have a stronger influence on development
  • Impact of nature and nurture on development changes throughout the life span
  • History of the developmental behavior genetic perspective

Davis, Haworth, & Plomin, 2009

  • Studied genetic stability and change in the development of general cognitive ability (g) during transition from early to middle childhood
  • Twins Early Development Study (TEDS) recruited families of twins born in Wales and England between 1994 and 1996
  • Used 8,791 twin pairs from TEDS
  • Administered verbal and nonverbal tests to kids (2-4) and mental ability tests to kids (7, 9, and 10)

Tucker-Drob et al. (2011) state that future research should investigate specifically which aspects of SES contribute to Gene x SES effects in order to provide better recommendations for policy. Which aspects of SES do you think are most influential in Gene x SES effects? What are some implications of these findings that could be used to make empirically based recommendations for policy and intervention?

Davis, Haworth, & Plomin, 2009

Sara Tackett

The researchers found that shared environmental factors did not significantly explain adolescent peer college orientation, peer delinquency, or peer popularity. Why do you think this was the case? Do you think this is accurate? What factors do you consider to be most significant in explaining these areas in adolescents?

  • Heritability of g increases as children grow up
  • Early childhood: shared environmental factors account for 74% of variance and genetic influence accounts for 23% of variance
  • Middle childhood: shared environmental factors account for 33% of variance and genetic influence accounts for 62% of variance

The researchers had conflicting results. Environmental effects were found to account for the majority of the variance observed in peer delinquency in the NEAD sample, but genetic effects were more influential in the CAP sample. Keeping in mind that the NEAD sample consists of twin and sibling data and the CAP sample consists of adoptive and nonadoptive sibling data, do you see any reason for these inconsistent findings? What are some implications of these results?

Goldhaber (2000)

  • Use animal and human research methods
  • Kinship studies: study MZ and DZ twins
  • Adoption studies: attempt to make genes and environment separate

Sandra Scarr

  • Genes drive experience, and thus, development
  • Genes have greater influence on development, because genotype precedes environment

Robert Plomin

  • When heritability estimates change throughout development, they increase
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