Modules 5: Behavior Genetics and Evolutionary Psychology

What is going to happen to Jaden Agassi? DAD: ANDRE AGASSI 8 time Grand Slam singles champion Olympic gold medal in singles Won all 4 titles on 3 surfaces Won Tennis Masters cup Won Golden Slam MOM: STEPHANIE GRAF 22 time Grand Slam singles champion Won all 4 Grand Slams on 3 surfaces at least 4 times each World # 1 for 377 weeks

Nature vs. Nurture Nature: Nurture: “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)

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

Chromosomes and Genes: Their Location and Composition Nucleus Chromosome Gene Cell DNA Chromosomes rod-shaped structures within cells that carry genes. Genes functional units of heredity which are composed of DNA and specify the structure of proteins. DNA (dioxyribonucleic acid) transfers genetic characteristics by way of coded instructions for the structure of proteins. 23 pairs – 1 from Mother 1 from Father

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 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

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 person-to-person variation can be attributed to genetic differences. Some variables such as height are highly heritable, other variables such as musical ability or social skills are moderately heritable.

Behavior Genetics approach to the nature/nurture issue? Experimental approach: Hold genes constant – vary the environment Hold environment constant – vary the genes

How can we hold environment constant? Adopted Children Compare the traits of adopted siblings  similarity indicates influence of the environment Compare the correlations between the traits of adopted children and those of their biological and adoptive parents influence of heredity vs. environment

How can we hold genes constant? Twins Identical twins Fraternal Same sex only 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

Nature vs. Nurture on IQ Greater genetic similarity  greater IQ similarity A substantial contribution of genes to IQ

Siblings and Adopted siblings They have little resemblance Environmental factors that are shared by siblings do not influence them much WHAT IS IT THAT IS ABOUT THE ENVIRONMENT, THAT INFLUENCES US? Unique experiences Gene-Environment interaction

Biological Roots of Personality: interaction of nature - nurture

Facts About Heritability Heritability estimates do not apply to individuals, only to variations within a group. Even highly heritable traits can be modified by the environment.

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. Some of the goals of evolutinary psychology: 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. Key assumption: Psychological traits, like physical traits are (a) heritable, (b) can differentially contribute to the reproductive success of individuals, and hence, (c) can be shaped naturally. Some of the objectives of evolutinary psychology: 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. Start by asking what sorts of challenges human beings might have faced (enemies – food etc) and then draw inferences about which behavioral tendencies might have been selected by nature to overcome these challenges. E.g. avoiding poisonous food and an innate dislike for bitter tastes.

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)

Natural Selection works Dog breeds Belyaev’s experiment with foxes Animal breeders everywhere How about people?

Evolutionary Psychology’s explanation of mating preferences Men preferred attractive physical features suggesting youth and health and fertility Women preferred resources and social status Evolutionary Psychology’s explanation of mating: “We behave in ways that maximizes our chances of passing on our genes, and to help our close biological relatives, with whom we share genes, to do the same.” “Romantic love is an adaptation that fostered the reporoductive success of our ancestors: bonding two people who would likely become parents of an infant who would need their reliable care.”

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.

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 Natural Selection the principle that, among the range of inherited trait variations, those that lead to increase reproduction and survival will most likely be passed on to succeeding generations Mutations random errors in gene replication that lead to a change in the sequence of nucleotides the source of all genetic diversity Animals with features suited to demands of environment will survive better than those with less well-adapted features. Those well-adapted animals will reproduce more successfully.

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?