Intro

 What causes our striking diversity and also our
shared human nature?
 How much are human differences shaped by our
differing genes?
 How much are human differences shaped by our
environment?
 Unit3C tells the complex story of how our genes
(nature) and environments (nurture) define us.
Behavior Genetics: Predicting
Individual Differences

 Behavior Geneticists: study our differences and
weigh the effects and interplay of heredity and
environment
 Jaden Agassi: tennis talent because of genes or tennis
environment?
Behavior Genetics: Predicting
Individual Differences

 _______________: threadlike structures made of
DNA molecules that contain genes
 ______: complex molecule containing the genetic info
that makes up the chromosomes
 __________: small segments of giant DNA molecules,
heredity
Genes: Our Codes for Life

Each human cell contains ___ total chromosomes
 ___ donated from your mother’s egg
 ___ donated from your father’s sperm
Each chromosome is paired up with a partner,
and each chromosome pair contains thousands
of genes, which also occur in pairs.
 Sometimes a member of a pair has a louder voice,
always expressing itself and masking the other,
different, member of the pair…this is a dominant
gene.
 A recessive gene is one that is masked when the
paired genes are different.
Behavioral Genetics

 Every other human is close to being your identical
twin -- _____% the same
 Genome: complete instructions for making an
organism
 Consists of all the genetic material in that organisms
chromosomes
 Slight variations from common pattern give us clues to
our uniqueness (why one has cancer, tall, shy)
 Genotype refers to a person’s genetic makeup
 Phenotype refers to the ways in which a person’s
genotype is manifested in observable characteristics.
Identical vs. Fraternal
Twins

 Identical Twins: develop from a single fertilized egg
that splits in two
 Genetically identical(human clones)
 However:
 They don’t always have the same number of copies of
those genes (why one may get sick)
 1 in 3 don’t share placenta (one may have more
nourishment)
Identical vs. Fraternal
Twins

 Fraternal Twins: develop from separate fertilized
eggs
 Share fetal environment but are genetically no more
similar than ordinary brothers & sisters

Separated Twin Studies

 2 Jim’s: woodworking, Chevy, Nascar, Miller Lite,
son named James Alan (Allan), Dog named Toy,
Migraines, High Blood Pressure, Chain smoking,
Personality, Intelligence, Heart Rate, Brain Waves
 Oskar & Jack:
 One raised Catholic Nazi
 One raised as a Jew in the Caribbean
 Similarities: spicy food, fall asleep in front of tv, flushed
toilet before using it, rubber bands wrist, dipped toast in
coffee, physical attributes, attitudes, interests, fears

 http://www.youtube.com/watch?v=Wd5Y3-F79LY
Separated Twin Studies

 Criticisms of twin studies:
.
.
.
Separated Twin Studies

 Criticisms of twin studies:
 If any two strangers were to spend hours comparing
their behaviors and life history, they would discover
many coincidental similarities
 People with similar economic and cultural
background (like many separated twins) exhibit many
similarities
 Many separated twins met years before they were
tested
Biological vs. Adoptive
Relatives

 Behavior geneticists also look at how:
 Genetic relatives (biological parents & siblings) and
environmental relatives (adoptive parents & siblings)
impact development
 For any trait, we can ask whether adopted children are
more like:
 Biological parents who contributed genes (nature)
 Adoptive parents who contributed home environment
(nurture)
 What do you think will have a greater impact?
Biological vs. Adoptive
Relatives

 Findings: people who grow up together, whether
biologically related or not, do not much resemble
one another in personality
 Extraversion/Agreeableness: adoptees are more
similar to their biological parents
 Compare to your siblings!
 Environment shared by a family’s children has
virtually NO discernible impact on their
personalities
 Link between heredity and development of
personalities
Biological vs. Adoptive
Relatives

 Why are children in the same family so different?
 Why does shared family environment have so
little effect on children’s personalities?
.
.
.
Heritability

 Using twin and adoption studies, behavior
geneticists can mathematically estimate, the
heritability of a trait
 Heritability: variations among individuals that we can
attribute to their differing genes
 If all schools were of uniform quality, all families equally
loving, and all neighborhoods equally healthy, then
heritability would increase because differences due to
environment would decrease
Heritability

 If heritability of intelligence is 50%
 Does that mean that your intelligence is 50% genetic?
 __________
 Genetic influence explains 50% of the observed
variation among people
 Heritability refers to the extent to which differences
among people are attributable to genes.
Nature vs. Nurture

 Humans have enormous adaptive capacity
 Person #1, barefoot = callused feet (biological
adaption)
 Person #2, shoes = tenderfoot
 Differences obviously from ______________
 Genes & Environment work together
 Genes respond to environments
Nature vs. Nurture

 Interaction between genes and environment tell us
genes are self-regulating
 Genes do not lead to the same result no matter the
context, genes react
 Example: Butterfly that changes colors due to changes in
temperature in various seasons
 People with identical genes but differing experiences
therefore have similar though not identical minds
Nature vs. Nurture

 At least one known gene will, in response to major
life stresses, code for a protein that controls a
neurotransmitter involved in depression
 By itself, the gene doesn’t cause depression
 What else would be an influence?
 Human differences result from both genetic and
environmental influences
Gene-Environment
Interaction

 Interaction: interplay that occurs when the effect of
one factor (environment) depends on another
factor(heredity)
 1.) Environments trigger gene activity (depression)
 2.) Certain traits evoke significant responses in others
(impulsive student evokes angry response from
teacher)
 Our genes affect how people react to and influence us =
possible changes in our behavior
Gene-Environment
Interaction

 Good looks will get you that job, promotion and
raise
Review

 How have heredity and environment influenced
who you are today?