1. Modules 5: Behavior Genetics and Evolutionary Psychology

2. Source of similarities and differences
Similarities with other people such as developing a language, showing similar emotions, preferences for certain tastes
Universal human behavior
Individual differences such as ability to learn math, response to a stressful situation, traits such as extroversion
Sources of variability in mental processes and behaviors:
Nature (genes, biology, heredity....) or
Nurture (experience & learning)

3. Nature vs. Nurture Nature- nativism Nurture- empiricism
“In the actual race of life…the determining factor is heredity” E.L. Thorndike (1903)
Nurture- empiricism
“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)

4. 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
If he becomes a tennis player – because of the genes or because of his constant exposure to tennis?

5. 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

6. Behavior Genetics Every cell nucleus in the body contains the
Chromosome
Gene
Cell
DNA
Every cell nucleus in the body contains the
genetic code for the entire body.

7. 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 with other humans
We share about 60% of our genes with a fruit fly

8. 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.

9. 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.
In similar environments- individuals differences are likely to be due to heredity factors 9

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

11. 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

12. Holding genes constant – Adopted Twins
Identical twins who were separated early in life and reared apart
Similarities  Genetic influences

13. Identical vs. fraternal twins
Varying genes in a controlled way
Holding environment constant
Allows the estimation of the effects of genes vs. environment

14. 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
WHAT ABOUT THE ENVIRONMENT INFLUENCES US?
Unique experiences
Gene-Environment interaction
Research: adopted children’s personality traits are more similar to their biological parents.
But this similarity decreases by time..... 14

15. Example: IQ Greater genetic similarity  greater IQ similarity
A substantial contribution of genes to IQ

16. 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.
Rather than saying they genes and environment both affect our traits and behaviors we should say they interact
Two babies --- born at the same time – one ie more social, attractive and easy going, other is not.
The first one will also attract more attention, affection and develop differently than the latter one.
Child + parent interaction...
Child’s nature is interacting with the nature porvided by the parent!

17. 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
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.

18. How Natural Selection Works
Genotype
Genetic structure
Phenotype
Observable characteristics

19. 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)

20. 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.

21. 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.
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. 21

22. Evolutionary Psychology: Key assumption
Like physical traits, psychological traits are:
heritable (inherited from our ancestors)
can contribute to the survival and reproductive success of individuals, and therefore
can be shaped naturally.
E.g. avoiding poisonous food helped us developing an innate dislike for bitter tastes.
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.
genetic inheritance from our ancestors –
Genetic predispositions inherited from our ancestors that promoted their survival and reproduction.
e.g., tendency to automatically recognize angry, smiling faces
e.g., parental protection seems to be universal

23. 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.
Because of different kinds of survival and mating problems, the 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 females understand that a male has good resources?

24. 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.”

25. More socially dominant
Men are found to be:
More violant
More socially dominant
More interested in the youth/beauty of their sexual partners
More sexually jealous and possessive over partners
More prone to have sex with partners they don’t know well
More inclined towards polygomy
Women emphasize:
Mate’s status
Financial resources
Willingness to commit to a relationship

26. Critique of Evolutionary Psychology
Hindsight approach: Explaining sex differences after observing what those differences are.
Are observed differences justified or morally right?
Can these differences be explained by social structural factors?
Does evolutionary psychology justify gender inequality?