Biological Bases of Behaviour - Interaction of Heredity & Environment

Nature vs. Nurture

  • The nature-nurture issue is a long-standing debate about the contributions of genes and experience to psychological traits and behaviors.
  • Modern science sees traits and behaviors arising from the interaction of nature and nurture.
  • Evolutionary psychology: studies the evolution of behavior and the mind, using natural selection principles to understand human similarities.
  • Behavior genetics: studies the relative power and limits of genetic and environmental influences on behavior, focusing on individual differences.

Evolutionary Psychology

  • Charles Darwin's principles of natural selection guide evolutionary psychologists.
  • Evolutionary psychologists seek to understand how genetics and environment interact, leading to genetic changes that fit the environment.

Natural Selection

  • Natural selection is the principle that inherited traits enabling survival and reproduction in a specific environment are more likely to be passed on.

Darwin’s Principles

  • Organisms' offspring vary and compete for survival.
  • Biological and behavioral variations increase survival chances in specific environments.
  • Surviving offspring are more likely to pass their genes to the next generation.
  • Over time, population characteristics may change.

Natural Selection Process

  • Variation: Genetic variation exists within a population and can be inherited.
  • Overproduction: Overproduction of offspring leads to competition for survival.
  • Adaptations: Individuals with beneficial adaptations are more likely to survive and pass on their genes.
  • Selection: Over many generations, allele frequency changes, leading to evolution.

Selective Breeding Example

  • Researchers Belyaev and Trut selectively bred the tamest foxes over 30 generations (40 years).
  • This resulted in docile, eager-to-please, domesticated animals.
  • Psychological traits can be selected as well as physical traits.

Mutation

  • A mutation is a random error in gene replication that leads to a change.

Naturally Occurring Selection

  • Historical genes provide a capacity to learn and adapt to varied environments.
  • Genes and experience together wire the brain.
  • Adaptive flexibility in responding to different environments contributes to fitness (ability to survive and reproduce).
  • We may be biologically prepared for a world that no longer exists.

Behavioural Genetics

  • Behavior geneticists study the relative power and limits of heredity and environmental influences.
  • Heredity (nature): Genetic transfer of characteristics from parent to offspring.
  • Environment (nurture): Every non-genetic influence, from prenatal nutrition to surroundings.

The Human Genome

  • In human genetics, there are more similarities than differences.
  • About 95% of genetic variation exists within populations.
  • Similarities developed through natural selection.
  • Survival needs led to universal human tendencies.
  • Genetics predispose us to particular behaviors, similar to physical traits.

Twins - Monozygotic

  • Monozygotic twins develop from a single fertilized egg that splits in two, creating genetically identical organisms.
  • Exceptions:
    • Identical genes but not the same number of copies, explaining variation.
    • Sharing a placenta vs. individual placentas.

Twins - Dizygotic

  • Dizygotic twins develop from separate fertilized eggs, share a maternal prenatal environment, and are no more alike than siblings.

Twin Studies

  • Twin studies help understand the roles of heredity and environment.
  • Identical twin with autism spectrum disorder: 3/4 risk of similar diagnosis, fraternal twin: 1/3 risk (Ronald & Hoekstra, 2011).
  • Identical twins are more alike in extraversion and neuroticism (Kandler, 2011; Laceulle et al., 2011; Loehlin, 2012).
  • Drinking and driving convictions are 12 times greater among identical twins than fraternal twins (Beaver & Barnes, 2012).

Twins Reared Apart

  • Thomas Bouchard and colleagues studied 74 pairs of identical twins raised apart.
  • They found similarities in tastes, physical attributes, personality, abilities, attitudes, interests, and fears.
  • The