1. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Shared Human Nature
Behavior Genetics
In all cultures, we start fearing strangers at about 8 months
We are uniquely similar as a human race
Genes = Nature
Environments = Nurture
Both genes and environment play a part in shaping us
Behavior Genetics is the study of the relative power and limits of nature and nurture on behavior

2. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Genes
Genes
Each human has 46 chromosomes
23 from mother’s egg
23 from father’s sperm
Chromosomes are found within a cell’s nucleus
DNA is found within each chromosome
Genes are found within each strand of DNA
Genes may be active (“turned on”) or inactive (“turned off”).
Environmental events are responsible for “turning on” genes.
Our DNA sequence is 96% the same as a chimpanzee.
Our observable traits such as height are influenced by our genes.

3. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Twin & Adoption Studies
Twin & Adoption Studies
Identical Twins – develop from a single fertilized egg that splits in two (identical genes)
May not always have the same number of copies of those genes
1 in 3 sets develop in separate placentas
Fraternal Twins – develop from separate fertilized eggs (no more genetically similar than any other sibling)
In virtually all ways, identical twins are more similar than fraternal twins
Shared experiences
Divorce rates
Genes more than shared experiences account for differences in identical twins

4. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Twins
University of Minnesota Study
Separated identical twins Jim Lewis and Jim Springer had amazingly similar life experiences without having contact with one another for 38 years
When measuring personality, intelligence, heart rate, and brain waves, their results were as those of the same person tested twice!
U of MN researcher Bouchard studied 80 pairs of identical twins that were raised apart
Found similarities in personality, abilities, attitudes, interests, fears
“…the plural of anecdote is not data…”

5. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Biological vs Adoptive Relatives
Biological vs Adoptive Relatives
Key question: Are adopted children more like their biological parents or their adoptive parents?
In the area of personality, they are closer to biological parents
Environments shared by children have NO discernible impact on personality
Parenting has less influence on personality, but a greater influence on:
Attitudes
Values
Manners
Faith/Religious Views
Political Views

6. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Adoptions
Temperament & Heredity
Adoptive parents are carefully screened; natural parents are NOT
7/8 adopted children feel a close bond to adoptive parents
Big Picture: children benefit from adoption
Many times adopted children outperform their biological parents (stability, intelligence)
Temperament = emotional reactivity and intensity
Irritable, intense, unpredictable
Cheerful, relaxed, predictable
Temperament persists over the long haul, although some change is possible
Heredity predisposes temperament differences

7. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Temperament & Heredity
Heritability
“Our biologically rooted temperament helps form our enduring personality.”
Heritability – the extent to which variation among individuals can be attributed to their differing genes.
We can never say what % of an individual’s intelligence or personality is actually inherited.
The key here is “differences among people”

8. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Group Differences
Nature and Nurture
Individual differences in height and weight are highly heritable.
Differences in males vs females or in people of varying ethnicities cannot be easily explained through heritability.
Humans have an enormous adaptive capacity.
Genes are self-regulating
The same gene that makes the African butterfly green in the summer, makes it brown in the fall
Humans with very similar genes may have very different experiences, therefore the genes may be expressed differently.

9. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Nature and Nurture
Nature and Nurture
Eating disorders are primarily a Western cultural phenomenon
Not found in most other cultures
Definitely a product of both nature and nurture
“Heredity deals the cards; environment plays the hand.”

10. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Gene-Environment Interaction
Gene-Environment Interaction
Baby who is attractive, sociable, and easy-going may attract more affectionate and stimulating care.
This in turn may lead the individual to be a warmer and more outgoing person, more often seeking activities and friends.
Children experience being parented based on their own qualities.
We should start thinking “nature via nurture”.

11. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Molecular Genetics
Molecular Genetics
Goal
Find genes that influence human traits
Explore mechanisms that control gene expression
Procedure
Seek out families that have had a disorder across several generations
Draw blood from both affected and healthy family members
Examine DNA to look for differences and hopefully identify genes on which to focus their attention

12. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Ethical Considerations
Evolutionary Psych
Might early testing of embryonic qualities lead to discrimination?
Boys valued in China
Some famous Americans were troubled people
Individuals may parent differently knowing their child is labeled “at risk”
Organisms varied offspring compete for survival
Biological and behavioral variations increase reproductive and survival chances
Offspring that survive are more likely to pass their genes on to next generation
Over time, population characteristics change

13. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Natural Selection & Adaptation
Evolutionary Success
Dmitry Belyaev – Russian scientist who studied possibility of domesticating foxes
Carefully selected the most tame, docile foxes
Over 30 generations of mating, the desired traits prevailed
“Our shared human traits were shaped by natural selection acting over the course of human evolution.” -Steven Pinker -no more than 5% of genetic differences among humans arise from population group differences; 95% comes within groups

14. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Evolutionary Success
Evolutionary Success
Women’s experience of nausea during the first 3 critical months of pregnancy serves as a protective mechanism for developing embryo. Certain bitter, strong tasting foods may be poisonous to the developing baby.
Sweet and fats once helped our ancestors survive famines
Today famine is not a concern in Western cultures, and those same traits lead to obesity and other disease

15. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Human Sexuality
Mating Preferences
In almost every human culture, men exhibit a stronger sex drive than women
Men more often than women attribute a woman’s friendliness to sexual interest
Helps to explain sexual harassment and date rape
Women’s approach to sex is usually more relational, and men’s more recreational
Men usually find women attractive if they have a youthful appearance (evolutionary explanation = able to reproduce)

16. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Mating Preferences
Mating Preferences
Men prefer youth and health in seeking a partner
Women prefer resources and social status in seeking a partner
Young, middle-aged, and older men prefer women in their child-bearing years
Women of all ages prefer men who seem dominant, mature, bold, and affluent (support and protection)

17. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Critiquing Evolutionary Perspective
Parents & Peers
The sexes, having faced similar adaptive problems, are far more alike than different
Evolutionary perspective usually works from a hindsight explanation, which makes it look more correct than it may be.
Rosenweig & Krech study on rats:
Rats living in an enriched environment developed a heavier and thicker brain cortex. (Brain weights and number of synapses both increased).
Those living in impoverished environments had thinner cortices.

18. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Parents & Peers
Parents & Peers
Stimulation by touch or massage help infants develop faster neurologically and gain weight faster.
Neural pathways are broadened or pruned, depending on their early usage.
In early childhood, excess neural connections are available – good time to learn another language.
Some language must be mastered by adolescence, or no language may be mastered. (critical period)

19. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Parents & Peers
Parenting
In early years especially, the brain operates by the principle: Use it or Lose it!
Are children easily wounded by normal parental mistakes?
“Two children in the same family (are on average) as different from one another as are pairs of children selected randomly from the population.” – Plomin & Daniels (behavior geneticists)
Children are NOT easily sculpted by parental nurture

20. UNIT 4: NATURE, NURTURE, & HUMAN DIVERSITY
Peer Influence
Peer Influence
Especially during childhood and adolescence, we seek to fit into groups.
Children get more of their culture from peers than from parents (adapt to peers characteristics).
Children seek out friends with similar interests/habits as their own.
Parents influence:
Education, discipline, responsibility, orderliness, charitableness, and ways of interacting with authority.
Peers influence:
Cooperation, popularity, and ways of interacting with peers.