6. Behavioral Genetics I

Stanford・2 minutes read

Behavior genetics examines genetic influences on behavior, focusing on shared traits among individuals with varying genetic relatedness, while studies have shown genetic components influence behavior traits such as gender differences. Prenatal environmental effects play a significant role in shaping lifelong traits and behaviors, challenging traditional genetic assumptions, with metabolic programming occurring during fetal development impacting risks of obesity, hypertension, and diabetes.

Insights

  • Behavior genetics examines genetic components of behavior, inferring genetic influences from shared traits among individuals with varying genetic relatedness, with a focus on controlling for shared genes and environment in studies.
  • Genetic influences play a significant role in behavior traits, such as gender differences in newborns and math skills among academically gifted children, highlighting the impact of genetic factors on various outcomes.
  • Prenatal environmental effects, including metabolic programming and epigenetic changes, have lifelong impacts on traits and behaviors, challenging traditional genetic assumptions and emphasizing the importance of early life experiences.

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Recent questions

  • What is behavior genetics?

    Behavior genetics examines genetic components of behavior.

  • How do genetic influences impact behavior traits?

    Genetic influences can affect behavior traits like gender differences.

  • What are the challenges in behavior genetics studies?

    Challenges include issues of paternity uncertainty and non-random placement.

  • How do prenatal environmental effects impact behavior traits?

    Prenatal environmental effects can shape lifelong traits and behaviors.

  • What role do mitochondria play in genetic inheritance?

    Mitochondria contain DNA inherited exclusively from the mother.

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Summary

00:00

Genetic influences on behavior: a critical analysis.

  • Apologies for flight delays; introduction to a new topic on behavior genetics.
  • Previous approaches discussed: sociobiological/evolutionary psychology and molecular biology.
  • Sociobiological approach: behavior evolves under selection rules, heritability, and evolution.
  • Molecular biology approach: evolution at DNA level, microevolution, macroevolution, punctuated equilibrium.
  • Shift to behavior genetics field, examining genetic components of behavior.
  • Criticisms of behavior genetics, including deterministic genetic inferences.
  • Strategy in behavior genetics: inferring genetic influences from shared traits among individuals with varying genetic relatedness.
  • Initial simplistic approach: universal traits in species indicate genetic influence.
  • More refined approach: observing behavioral traits in families to infer genetic influence.
  • Control for shared genes and environment in behavior genetics studies.
  • Comparison of identical twins to fraternal twins to determine genetic influence on shared traits.

14:16

Genetic Influences on Behavior and Mental Health

  • Monozygotic twins share more environmental factors than dizygotic twins, making it challenging to attribute differences solely to genetics.
  • Differences in behavior traits can be influenced by genetic factors, such as gender differences, even when environmental conditions are the same.
  • Studies have shown that newborn boys exhibit higher levels of activity and movement compared to newborn girls, suggesting a potential genetic influence.
  • Mothers interact differently with baby girls and baby boys from the very first moments of life, indicating early gender-specific environmental differences.
  • A study by Benbow and Stanley in the '80s revealed significant gender differences in math skills among academically gifted children, with boys scoring higher on average.
  • The study suggested a genetic basis for the observed gender differences in math skills, attributing them to biological factors due to identical educational environments.
  • Adoption studies, like the one conducted by Seymour Kety, examine shared traits between adopted individuals and their biological and adoptive parents to understand genetic influences on behavior.
  • Kety's study in Scandinavia found that individuals raised by adoptive parents with schizophrenia had a significantly higher risk of developing schizophrenia themselves, indicating a genetic component to the disorder.
  • Being raised in a household with a schizophrenic adoptive parent tripled the risk of a schizophrenia diagnosis, highlighting the impact of genetic factors on mental health outcomes.
  • The study emphasized the importance of genetic influences on behavior and mental health outcomes, challenging previous assumptions about the role of environment in shaping traits.

28:46

Genetic Legacy: Schizophrenia and Behavior Studies

  • Having a biological legacy of schizophrenia from biological parents results in a 9% incidence, a three-fold increase compared to the general population.
  • Individuals with a biological parent with schizophrenia, but raised separately, have an almost 10-fold higher chance of developing the disease.
  • In cases where individuals have a biological parent with schizophrenia and are raised by an adoptive parent with schizophrenia, the incidence rate rises to 17%.
  • The study highlighted the genetic component of psychiatric disorders, leading to further research on heritability in various traits like depression, alcoholism, and criminality.
  • Challenges in adoptive studies include issues of paternity uncertainty and non-random placement of adoptive children, affecting the accuracy of genetic studies.
  • Identical twins separated at birth became the gold standard for behavior genetics studies, offering a unique opportunity to study genetic influences in different environments.
  • Identical twins separated at birth studies revealed bizarre similarities in behavior, such as both twins flushing the toilet before and after use, indicating genetic influences.
  • The heritability of IQ, introversion/extroversion, and aggression was found to be around 50% in identical twins separated at birth studies.
  • Critiques of the identical twins separated at birth studies include non-random placement in adoptive families, leading to the need for comparisons with dizygotic twins.
  • Genetic influences are evident in behaviors like smiling, which occur universally in babies and even in fetuses during the third trimester, indicating genetic patterns.

43:16

Prenatal Environment Shapes Lifelong Traits and Behaviors

  • Social smiling is a behavior observed in babies at three months old, occurring universally even in congenitally blind or deaf babies.
  • Prenatal environmental effects are crucial, with the environment impacting traits that may be mistaken for genetic.
  • The assumption that environment begins at birth has been challenged, with prenatal environment having significant effects.
  • Hormonal influences from the prenatal environment can impact puberty onset and brain development.
  • Stress hormones in the prenatal environment can lead to lifelong effects like smaller brains, anxiety, and cognitive decline.
  • Prenatal stress can result in elevated glucocorticoid levels in offspring, affecting brain size and function.
  • The "grandmother effect" demonstrates non-genetic inheritance of traits due to prenatal environment.
  • Nutrients shared in the prenatal environment can lead to metabolic programming in fetuses, creating a thrifty phenotype.
  • The Dutch Hunger Winter of 1944 showcased how prenatal famine can impact fetal development and metabolic programming.
  • Prenatal environmental effects play a significant role in shaping lifelong traits and behaviors, challenging traditional genetic assumptions.

57:20

Fetal Metabolic Programming and Health Risks

  • The pancreas releases insulin to store nutrients efficiently in the bloodstream.
  • Kidneys are metabolically programmed to retain salt effectively.
  • Individuals born with a thrifty metabolism store nutrients efficiently.
  • Dutch Hunger Winter individuals show increased risks of obesity, hypertension, and diabetes due to metabolic programming.
  • Metabolic programming occurs during the second to third trimester of fetal development.
  • Fetal origins of adult disease is a significant field of study.
  • Epigenetic changes in genes related to insulin occur in Dutch Hunger Winter babies.
  • Increased exposure to estrogen during fetal life may lead to a higher risk of breast cancer later in life.
  • Prenatal exposure to certain flavors can influence preferences after birth.
  • Prenatal experiences, such as hearing a mother's voice, can impact newborn preferences.

01:11:36

Mitochondrial DNA and Indirect Genetic Effects

  • Mitochondria have their own DNA, leading to the hypothesis that they were once independent organisms that entered cells in a symbiotic relationship billions of years ago.
  • Mitochondria contain DNA critical for their function, inherited exclusively from the mother at fertilization.
  • Eggs contain mitochondria and transcription factors from the mother, influencing gene expression in offspring.
  • Transcription factors from the mother in fertilized eggs can lead to the inheritance of traits that are never expressed due to disruptions.
  • Environmental toxins can induce heritable traits that are not expressed, akin to Lamarckian inheritance.
  • Genetic material is not equally inherited from both parents due to mitochondrial DNA and imprinted genes.
  • Behavior can be influenced by genes, but indirect genetic effects can also play a significant role.
  • Heritability of physical traits like height can indirectly influence personality traits like extroversion.
  • In birds, social rank can be influenced by genes related to feather color rather than direct inheritance of rank.
  • Certain behaviors, like pecking at grubs in chicks, may be heritable but are actually mediated by indirect traits like pecking at toes.

01:26:25

Political Affiliation Heritability and Epigenetic Influences

  • Political party affiliation has a 70% heritability rate in the country, showing a strong link to parental behavior.
  • Conservatives tend to be more ambiguity-averse compared to progressives, a stable personality difference at political extremes.
  • Ambiguity tolerance is a mediating trait in political differences, more reliable than Kohlberg's Stage of Moral Development.
  • Aggression in rat and mouse strains is a genetic trait linked to neurobiology of pain sensitivity.
  • Epigenetics plays a crucial role in multigenerational inheritance of non-genetic traits, impacting gene regulation.
  • Neonatal handling in rats influences brain size, learning abilities, and lifespan, with maternal behavior changes being critical.
  • Maternal licking and grooming in rats affect offspring's behavior and brain development, showing multigenerational effects.
  • Epigenetic changes due to maternal care impact gene expression for stress hormones and receptors, leading to lifelong differences.
  • Early experiences cause persistent changes in gene expression, while later experiences can reverse some epigenetic patterns.
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