Genes vs. Environment

Genes vs. Environment

1. Genetic Influence

   • Intelligence
     • twin and adoption studies suggest that a large component of the variation in IQ is due to genetic factors
     • however, there's equally strong evidence for the effects of nurture
       • Flynn effect; the observation that IQs all over the world have increased by 20 points in 30 years
         • must be due to environmental enrichment
   • Mental illness
     • twin and adoption studies show that the closer 2 individuals are genetically, the more likely that both of them will develop the same mental disorder
       • EG. concordance rate for schizophrenia is 40% for MZ and 7% for DZ
     • however, clearly a significant environmental component
       • diathesis-stress model; individuals who have a genetic vulnerability (diathesis) for a disorder only develop is under certain conditions (stress)
   • Evolutionary explanations
     • natural selection; behaviour that leads to increased survival/reproduction will be selected and passed on via genes to subsequent generations
     • however genetic behaviours are modified by culture
       • Buss found 22% of females did NOT value ambition an industriousness more than males (cultural relativism)

2. Environmental Influences

   • Aggression
     • Bandura's view was that aggressive behaviour is mainly learned through observation and vicarious reinforcement
       • the key concepts of social learning theory (SLT)
     • Bandura suggested that this enables us to learn the specifics of aggressive behaviour
     • however, a person's biological make-up creates a potential for aggression and it is the actual expression of aggression that is learned
       • Coccaro (1997) studied twin pairs and found that nearly 50% of the variance in aggressive behaviour could be attributed to genetic factors
   • Neural plasticity
     • the ability of the brain, both in development and adulthood to be changed by the environment
     • Pascual-Leone (1995) - the region of the brain that controls finer movement increased in size in PP's required to play a piano finger exercise daily over 5 days
     • Edwards and Cline (1999) - studies with non-human animals have observed the way neurons shrink and grow in response to changing environmental conditions