Behavior Genetics and Evolutionary Psychology Module 5 1
Behavior Genetics and Evolutionary Psychology Behavior Genetics Genes, Nature and Nurture Gene- Environment Interaction Twin and Adoption Studies Evolutionary Psychology: Natural Selection 2
Source of Similarities and Differences Similarities such as showing similar emotions, following similar paherns in life Differences such as ability to learn math, response to a stressful situation Sources of variability in mental processes and behaviors Nature (genes, biology, heredity...) vs Nurture (experience & learning) 3
Behavior Genetics Nature Concentrates on the influence of heredity on the differences in human characteristics. Nurture Every non- genetic influence, from prenatal nutrition to the people and things around us (e.g., parents, peers, school, culture). 4
Nature: Nature and 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, tendencies, abilities... and race of his ancestors. J. B. Watson (1925) 5
Behavior Genetics: Predicting Individual Differences Behavior Geneticists study our differences and weigh the relative effects of heredity and environment. 6
Genes: Our Codes for Life Chromosomes (23 pairs) containing DNA (deoxyribonucleic acid) are situated in the nucleus of a cell. Genes are functional biochemical units of heredity which that make up the chromosomes 7
Genes: Our Codes for Life 8
Genome Genome is the set of complete instructions for making an organism. It contains all the genes in that organism. Thus, the human genome makes us human, (and the genome for drosophila makes it a common house fly). 9
Nature or Nurture: Estimate of Heritability Heritability A statistical estimate of the proportion of variance in a given population that is due to genetics. E.g., Heritability of.60 Some variables such as eye color and height are highly heritable, other variables such as eating habits is less heritable. 10
Nature or Nurture: Estimate of Heritability Study: 1. Fraternal twins (dizygotic) 2. Identical twins (monozygotic) 5. Adopted children 11
Twin Studies 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 12
Twin Studies Behavioral geneticists can estimate the heritability of a trait by comparing identical twins to fraternal twins. Identical twins Fraternal twins Same sex only Same or opposite sex 13
Adopted Children Studying adopted children allows researchers to compare correlations between traits of adopted children and those of their biological and adoptive relatives. 14
Adopted / Separated Twins Investigators have also studied identical twins who were separated early in life and reared apart same heredity, different environment 15
The greater the genetic similarity between two individuals, the more similar are their IQ scores. Differences between fraternal twins are greater than identical twins. 16
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Temperament and Heredity Temperament refers to a person s emotional reactivity and intensity and self- regulation. Easy temperament : even- tempered, intense mood is rare, adaptable. Difficult temperament: active, irritable and irregular in habits. Compared to fraternal twins, identical twins have more similar temperaments; these temperament differences persist. 18
Nature and Nurture Gene- Environment Interaction Some human traits are fixed, such as having two eyes. However, most psychological traits are liable to change with environmental experience. Genes and environment affect our traits individually, but more important are their interactive effects. 19
Personality: Interaction of Nature & Nurture 20
Hereditary vs. Environmental Influences Some rubber bands can stretch easier than others. But for the most part, they can be stretched to the same length.
Behavioral Development: Interaction of Genetic Factors and Experience Selective Breeding of Maze Bright and Maze-Dull Rats: Brightest males were mated with the brightest females and dullest males were mated with the dullest females. No parenting effect: maze-bright offspring raised by dull parents and vice versa do not make a difference. Tyron, 1940
Behavioral Development: Interaction of Genetic Factors This difference disappeared in a single generation, if those rats were raised in an enriched environment with more objects to explore and more social interaction. Impoverished environment: plain wire cage Enriched environment: tunnels, ramps, visuals, variation. Environment had greatest effect on genetically less capable rats. and Experience Although, bright rats had developed specific abilities that are useful in mazes, further work of Tyron showed that the dull rats were just as smart when tested on a variety of other tasks.
Early Experience Rosenzweig et al. (1972) 24
Gene-Environment Interactions 25
Evolutionary Psychology No more than 5% of the genetic variation among humans arise from population group differences. Around 95% of the variation exists within populations. 26
Gene-Environment Interactions Genes are not simple blue-prints, they react. Environments trigger gene activity Our genetically influenced traits also evoke significant responses in others. Depending on our traits we also actively select our environment (selection effect). 27
Consequently It is not nature vs. nurture but It is nature via nurture 28
Evolutionary Psychology: Understanding Human Nature Evolutionary psychology studies why we as humans are alike. Natural selection is an evolutionary process through which adaptive traits are passed on to ongoing generations because these traits help animals survive and reproduce. 29
Evolutionary Psychology Key assumption: Psychological traits, like physical traits are (a) heritable, (b) can differentially contribute to the reproductive success of individuals. What sorts of challenges human beings might have faced (enemies food etc) and which behavioral tendencies might have been selected by nature to overcome these challenges. 30
Human Traits A number of human traits have been identified as a result of pressures afforded by natural selection. Why do infants fear strangers when they become mobile? Why do people fear spiders and snakes and not electricity and guns? How are men and women alike? How and why do men s and women s sexuality differ? 31
Human Sexuality Gender Differences in Sexuality Males and females, to a large extent, behave and think similarly. All seek greatest likelihood of reproduction. Differences in sexes arise in regards to reproductive behaviors. Women mate wisely, men mate widely! 32
Gender, Evolution and Sexual Strategies Because of different kinds of survival and mating problems, the two sexes have evolved differently in the areas of aggressiveness, physical dominance, and sexual strategies. 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. How do males understand that a female has good resources? How do females understand that a male has good resources? 33
Research on Mating Preferences Males look for youthful appearing females in order to pass their genes into the future. Females look for maturity, dominance, affluence, and boldness. Data based on 37 cultures. 34
Men are found to be: More violent and socially dominant More interested in the youth/beauty of their sexual partners More jealous and possessive over partners More inclined towards polygomy...than women 35
esearch Research on Age Preferences One example of a seemingly universal feature of social behavior is the difference between men and women in the preference for younger versus older partners 36