Modules 5: Behavior Genetics and Evolutionary Psychology

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1 Modules 5: Behavior Genetics and Evolutionary Psychology Source of similarities and differences Similarities with other people such as developing a languag, showing similar emotions, following similar patterns in life Individual differences such as ability to learn math, response to a stressful situation Sources of variability in mental processes and behaviors: Nature (genes, biology, heredity...) or Nurture (experience & learning) Nature vs. Nurture Nature: In the actual race of life the determining factor is heredity E.L. Thorndike (1903) Nurture: Give me a dozen healthy infants and I guarantee to take any one at random and train him to become any type of a specialist I might select doctor, lawyer, artist, mechanic, even a beggar-man and thief regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors. J. B. Watson (1925)

2 The Nature-Nurture Question How much of our differences and similarities are due to our genes? How much of our differences and similarities are due to our environment? Behavior Genetics: Individual differences Evolutionary Psychology: Human similarities Behavior Genetics Nucleus Chromosome Gene Cell Every cell nucleus in the body contains the genetic code for the entire body. DNA Genes: Our Biological Blueprint Biochemical units of heredity that make up the chromosomes A segment of DNA that contains coded instructions to create protein molecules Transfers genetic characteristics by way of coded instructions for the structure of proteins. We have about 30,000-70,000 genes We share about 99.9% of our DNA We share about 60% of our genes with a fruit fly

3 Studying relative effects of nature & nurture: Heritability A statistical estimate of the proportion of the total variability in some trait that can be attributed to genetic differences. Expressed as proportion (e.g., 0.60 or 60/100): 60 % of variance in trait X can be attributed to genetic differences. Some variables such as height are highly heritable, other variables such as musical ability are moderately heritable. Facts About Heritability Heritability estimates do not apply to individuals, only to variations within a group. Even highly heritable traits can be modified by extreme stimulations in the environment. Behavior Genetics approach to the nature/nurture issue? Semi - Experimental approach:

4 How can we hold genes constant? Twins Identical twins Same sex only Fraternal twins Same or opposite sex Identical Twins develop from a single fertilized egg that splits in two, creating two genetically identical organisms Fraternal Twins develop from separate eggs genetically no closer than brothers and sisters, but they share the fetal environment Holding genes constant Adopted Twins Identical twins who were separated early in life and reared apart Similarities Genetic influences Identical vs. fraternal twins Varying genes in a controlled way Holding environment constant Allows the estimation of the effects of genes vs. environment

5 How can we hold environment constant? Adopted Children Compare the correlations between the traits of adopted children and those of their biological and adoptive parents influence of heredity vs. environment Compare the traits of adopted siblings similarity indicates influence of the environment Example: IQ Greater genetic similarity greater IQ similarity A substantial contribution of genes to IQ Nature & nurture interaction Genes (nature) and environment (nurture) work together. Genes provide the code for certain traits (predispositons) They also select / react to the environment Indeed genes and environment interact Genetically influenced traits evoke significant responses Environment triggers gene activity. As we grow older, we select environments well suited to our natures.

6 Evolutionary Psychology: What makes humans alike? The study of the evolution of behavior and the mind, using the principles of evolutionary theory and natural selection. Key question What are the similarities in social behavior across cultures and historical periods How Natural Selection Works Environmental pressure (changes in the environment) Competition (for resources) Selection of fittest phenotype (among a variety of phenotypes) Reproductive success (genotype corresponding to fittest phenotype passed to next generation) Frequency of that genotype (and phenotype) increases (in next generation) Evolution results in variations in genes Natural Selection Species with features suited to demands of environment will survive better than those with less well-adapted features. Those well-adapted species will reproduce more successfully. Mutations Random or unexplained errors in gene replication that lead to a change in the sequence of nucleotides If adaptive, mutations will prevail

7 Evolutionary Psychology: Goals To understand the genetic basis of psychological traits. To trace the evolution of human mind and brain To understand how some psychological traits may contribute to reproductive fitness and survival. Evolutionary Psychology: Key assumption Like physical traits, psychological traits are: (a) heritable (inherited from our ancestors) (b) can contribute to the survival and reproductive success of individuals, and therefore (c) can be shaped naturally. E.g. avoiding poisonous food helped us developing an innate dislike for bitter tastes. Nature s selection principle Nature selects behaviors that increase the likelihood of sending genes into the future Males compete with other males for access to females, and try to inseminate as many females as possible. Females conceive and carry only a limited number of pregnancies so they choose fewer more dominant males with good resources and high status.

8 Evolutionary Psychology s explanation of mating preferences Men preferred attractive physical features suggesting youth and health and fertility Women preferred resources and social status Critique of Evolutionary Psychology Hindsight approach: Explaining sex differences after observing what those differences are. Are observed differences justified or morally right? Does evolutionary psychology lead us to justify male promiscuity? Does evolutionary psychology justify gender inequality?