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Chapter 3 Nature vs. Nurture

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1 Chapter 3 Nature vs. Nurture
How do families, friends and culture affect the way we live?

2 Behavior Genetics Study the relative effects of genes and environment on behavior The nature vs. nurture debate

3 Genetics in Brief Genes – biochemical units of heredity that make up a chromosome Chromosome – Threadlike structures made of DNA molecules that contain genes (46 total, 23 from each parent) DNA (deoxyribonucleic acid) – complex molecule that contains genetic information that makes up chromosomes Cell -> Nucleus -> Chromosomes -> DNA -> Genes

4 Human Genome Genes made up of nucleotides (A,T,C, or G)
Genome – complete instructions for making an organism consisting of all genetic material in its chromosomes Humans have about 30,000 different genes Does anyone know the animal humans are most genetically related to?

5 Predisposition Genes are responsible for predisposing our appearance and behavior, not concretely determining either. Predisposition – a situation that allows something else to occur but doesn’t necessarily cause it to occur; “Her genetic makeup left her with a predisposition to develop Alzheimer's.” Mutations – random error in gene replication that lead to a change in genetic code

6 Charles Darwin and Evolution
Natural selection – the idea that , among the inherited trait variations, those contributing to survival will most likely be passed on to future generations Adaptation – species changing genetically to better survive in their environment

7 Class Discussion What correlation does economic/social status of a country have with reproduction rates worldwide if any? Why do people in poorer countries have more babies? And should they have more babies? Is this natural selection at work here? Why or why not?

8 Twin Studies: Score one for Nature
Identical twins – twins that develop from a single fertilized egg and then split in half; are genetically identical Fraternal twins – twins that develop from separate eggs; no more related genetically than normal siblings Twin studies have discovered that identical twins are strikingly similar is intelligence, attitude and even brain waves!

9 Fig. 12-14, p. 493 Figure 12.14: Twin studies of personality.
Loehlin (1992) has summarized the results of twin studies that have examined the Big Five personality traits. The N under each trait indicates the number of twin studies that have examined that trait. The chart plots the average correlations obtained for identical and fraternal twins in these studies. As you can see, identical twins have shown greater resemblance in personality than fraternal twins have, suggesting that personality is partly inherited. (Based on data from Loehlin, 1992) Fig , p. 493

10 Is personality largely inherited
Is personality largely inherited? The story of these identical twins would certainly suggest so. Although they were reared apart from 4 weeks after their birth, Jim Lewis (left) and Jim Springer (right) exhibit remarkable correspondence in personality. Some of the similarities in their lives—such as the benches built around trees in their yards—seem uncanny. Although they were reared apart from 4 weeks after their birth, Jim Lewis (left) and Jim Springer (right) exhibit remarkable correspondence in personality. Some of the similarities in their lives—such as the benches built around trees in their yards—seem uncanny.

11 Adoption Studies: Score another for nature!
Studies of adopted children show that they exhibit similar personality traits of their biological parents However, adopted children tend to be smarter, more productive and more successful than their biological parents Nurture is back in the game!

12 Fig. 9-13, p. 353 Figure 9.13: Studies of IQ similarity.
The graph shows the mean correlations of IQ scores for people of various types of relationships, as obtained in studies of IQ similarity. Higher correlations indicate greater similarity. The results show that greater genetic similarity is associated with greater similarity in IQ, suggesting that intelligence is partly inherited (compare, for example, the correlations for identical and fraternal twins). However, the results also show that living together is associated with greater IQ similarity, suggesting that intelligence is partly governed by environment (compare, for example, the scores of siblings reared together and reared apart). (Data from McGue et al., 1993; Plomin & Spinath, 2004) Fig. 9-13, p. 353

13 Environment Matters Are parents to blame for success/failure of children? Studies say “not really”. Siblings raised together tend to be as different personality-wise as two random people on the street.

14 Early Learning and Brain Development
For our brains to reach their developmental potential, early experience is CRITICAL. Children raised in abusive homes tend to be less intelligent that children raised in loving environments. Score one for nurture!

15 Peer and Parent Influence
Peers hold a heavy influence on the behaviors of individuals (i.e. smoking, drinking, promiscuity ) Bandwagon phenomenon “Fitting In” Parents influence behaviors of children by supplying them the environment from which they have to work within (i.e. parents “choose” which neighborhood to live in)

16 Peer Influence Children, like adults, attempt to fit into a group by conforming. Peers are influential in such areas as learning to cooperate with others, gaining popularity, and developing interactions. Ole Graf/ zefa/ Corbis

17 Parenting Influences Children’s
Parenting does have an effect on biologically related and unrelated children. Parenting Influences Children’s Attitudes, Values Manners, Beliefs Faith, Politics

18 Cultural Influence Culture – shared attitudes and beliefs of a group passed on from one generation to the next. Norms – understood rules for accepted and expected behavior; prescribe “proper” behavior Individualism – giving priority to one’s goal over the goals of the group Collectivism – giving priority to the group’s goal over the goal of the individual

19 Gene-Environment Interaction
Genes can influence traits which affect responses, and environment can affect gene activity. A genetic predisposition that makes a child restless and hyperactive evokes an angry response from his parents. A stressful environment can trigger genes to manufacture neurotransmitters leading to depression.

20 Some Traits Show More Heritability Than Others
Height Temperament refers to a person’s stable emotional reactivity and intensity. Identical twins express similar temperaments, suggesting heredity predisposes temperament. As environments become more similar, heredity as a source of difference become more important (since difference due to environment has decreased).

21 Gene-Environment Interaction
Genes and environment affect our traits individually, but more important are their interactive effects. Preview Question 4: What is the promise of molecular genetics research? Alessia Pierdomenico/Reuters/Corbis Rex Features People respond differently to Rowan Atkinson (Mr. Bean) than Orlando bloom.

22 Culture and Child-Rearing
Westernized Cultures Asian-African Cultures Responsible for your self Responsible to group Follow your conscience Priority to obedience Discover your gifts Be true to family-self Be true to yourself Be loyal to your group Be independent Be interdependent

23 Developmental Similarities Across Groups
Despite diverse cultural backgrounds, humans are more similar than different in many ways. We share the same genetic profile, life cycle, capacity for language, and biological needs. Copyright Steve Reehl

24 Variation Over Time Culture changes over time. The rate of this change may be extremely rapid. In many Western countries, culture has rapidly changed over the last 40 years. This change cannot be attributed to changes in the human gene pool because genes evolve very slowly.

25 Gender Development Based on genetic makeup, males and females are alike, since the majority of our inherited genes (45 chromosomes are unisex) are similar. Gender is determined by only one chromosome. Males and females differ biologically in body fat, muscle, height, onset of puberty, and life expectancy. Preview Question 10: What are some ways in which males and females tend to be alike and to differ?

26 Biology of Sex Biological sex is determined by the twenty-third pair of chromosomes. If the pair is XX, a female is produced. If the pair is XY, a male child is produced.

27 Sexual Differentiation
In the mother’s womb, the male fetus is exposed to testosterone (because of the Y chromosome) which leads to the development of male genitalia. If low levels of testosterone are released in the uterus, the result is female.

28 The average…than the average man.
Physical Differences The average…than the average man. woman begins puberty 2 years earlier woman lives 5 years longer woman has 70% more body fat and tend to carry it in different areas of the body woman has 40% less muscle woman is 5” shorter woman is far less likely to be colorblind woman is doubly vulnerable to depression and anxiety woman’s risk of developing an eating disorder is 10x greater

29 Psychological Differences
The average man is 5x more likely to commit suicide or suffer alcohol dependence than the average woman. The average man is more likely to develop autism, ADHD or personality disorder than the average woman.

30 Gender Differences in Aggression
Men express themselves and behave in more aggressive ways than do women. This aggression gender gap appears in many cultures and at various ages. In males, the nature of this aggression is physical. In the US, the male-to-female arrest ratio for murder is 10:1.

31 Gender and Social Power
In most societies, men are socially dominant and are perceived as such. In 2005, men accounted for 84% of the governing parliaments.

32 Gender Differences and Connectedness
Young and old, women form more connections (friendships) with people than do men. Girls tend to play in smaller groups with more intimate relationships. Boys emphasize competition, freedom and self-reliance while playing in larger groups. Oliver Eltinger/ Zefa/ Corbis Dex Image/ Getty Images

33 Gender Roles Our culture shapes our gender roles — expectations of how men and women are supposed to behave. Gender Identity — means how a person views himself or herself in terms of gender. Preview Question 11: How do nature and nurture together form our gender?

34 Gender Roles: Theories
Social Learning Theory proposes that we learn gender behavior like any other behavior—reinforcement, punishment, and observation. Gender Schema Theory suggests that we learn a cultural “recipe” of how to be a male or a female, which influences our gender- based perceptions and behaviors.

35 Reflections on Nature and Nurture

36 Evolutionary Psychology: Understanding Human Nature
Evolutionary psychology studies why we as humans are alike. In particular, it studies the evolution of behavior and mind using principles of natural selection. The following traits would benefit humans in that they would provide an advantage for survival and reproduction: The mental capacities for acquiring language. The ability to infer emotion in others and to cooperate with others. The preference for healthier, more fertile mates. Preview Question 4: How do evolutionary psychologists use natural selection to explain behavior tendencies?

37 Evolutionary Success Helps Explain Difference
No more than 5% of the genetic differences among humans arise from population group differences. Therefore, 95% of genetic variation exists within populations. The typical genetic difference between two Icelandic villagers or between two Kenyans is much greater than the average difference between to the two groups.

38 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?

39 Question (summarized)
Human Sexuality Gender Differences in Sexuality Males and females, to a large extent, behave and think similarly. Differences in sexes arise in regards to reproductive behaviors. In the U.S.: Question (summarized) Male Female Casual sex 58% 34% Sex for affection 25% 48% Think about sex everyday 54% 19% Preview Question 5: How might and evolutionary psychologist explain gender differences in mating preferences?

40 Natural Selection & Mating Preferences
Natural selection has caused males to send their genes into the future by mating with multiple females since males have lower costs involved. However, females select one mature and caring male because of the higher costs involved with pregnancy and nursing.

41 Mating Preferences Males look for youthful appearing females in order to pass their genes into the future. Females, on the other hand, look for maturity, dominance, affluence and boldness in males. Data based on 37 cultures.

42 Mating Preferences Men are typically more attracted to a woman whose waists are roughly a third narrower than their hips – a sign of future fertility. Men are attracted to women who are at the age of peak fertility (which has shifted over time). Women are more attracted to men who seem more mature, dominant, bold and affluent.

43 Critiquing the Evolutionary Perspective
Evolutionary psychologists take a behavior and work backward to explain it in terms of natural selection. Evolutionary psychology proposes genetic determinism and undercuts morality in establishing society. Preview Question 6: What are the key criticisms of evolutionary psychology? Where genders are unequal, gender preferences are wide, but when they are closely equal, preferences narrow down.

44 Evolutionary Psychologists Reply
Evolutionary psychologists argue that we need to test behaviors that expound evolutionary principles. Evolutionary psychologists remind us how we have adapted, but do not dictate how we ought to be. Males and females are more alike than different, and if we study these differences we can establish their causes.

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