nature, nurture, and human diversity chapter 4

Nature, Nurture, and Human Diversity

Chapter 4


What causes our striking diversity in psychological functioning, and also our shared identity?

People differ in many aspects of psychological functioning. For example, some people possess a “Type A” personality and are aggressive, ambitious, and controlling, whereas others possess a “Type B” personality and are passive and easy-going.

Credit: Kjetil Ree

People differ in many aspects of psychological functioning. For example, some people possess a “Type A” personality and are aggressive, ambitious, and controlling, whereas others possess a “Type B” personality and are passive and easy-going.

Credit: Luca Galuzzi

Yet, we are also similar in some aspects of our psychological functioning. For example, whether we live in the Arctic or tropics, we divide the color spectrum into similar colors.

Farbentafel, Wilhelm von Bezold


Behavioral Genetics

The study of effects of environmental and genetic factors, and their interplay, on differences in psychological traits


Behavioral Genetics

Genes: Our Codes for Life


Every cell in your body contains chromosomes—23 donated from your mother, and 23 from your father.


Each chromosome is made up of two strands of DNA connected in a double helix. Genes are small segments of DNA molecules.


James Watson and Francis Crick with their DNA model at the Cavendish Laboratories in 1953. Photograph copyright A. Barrington Brown.


Behavioral Genetics

Twin and Adoption Studies

Identical Versus Fraternal Twins

Identical twins develop from a single fertilized egg and are genetically identical, whereas fraternal twins develop from separate fertilized eggs and share half their genes, just like siblings.

Credit: Derek Oliver (AP)

Correlation Between IQs of Family Members

Identical twins reared together .86Fraternal twins reared together .60Siblings reared together .47

(Bouchard & McGue, 1981)


Separated Twins

Even identical twins separated at birth and raised apart tend to be more similar in their psychological makeup than fraternal twins.

Credit: Bob Sacha

Jim Lewis and Jim Springer, identical twins, first met at the age of 39. Lewis was a security. guard, Springer a deputy sheriff. Both married, and divorced, a woman named Linda—and remarried a Betty.

Separated Twins

Credit: Bob Sacha

Lewis had a son named “James Alan” and Springer a son named “James Allan”—and both shared a taste for Miller Lite and enjoyed watching Nascar.

Separated Twins

Credit: Bob Sacha

Separated Twins

Personality, Intelligence

Abilities, Attitudes

Interests, Fears

Brain Waves, Heart Rate

Separated Twins

Obviously, some of these similarities are pure coincidence. But research has revealed that identical twins separated at birth are indeed more similar to less genetically-related pairs in a number of traits.

Biological Versus Adoptive Relatives

Are adopted children more alike their biological parents, who contributed their genes, or their adoptive parents, who contribute a home environment?



Child and biological parent by whom child is reared .42Child and biol. mother separated from the child by adoption .31Child and unrelated adoptive mother .17

(Horn, Loehlin, & Willerman, 1979)

Surprisingly, in many traits, adoptive children do not closely resemble their adoptive parents and are more similar to their biological parents.



Behavioral Genetics

Heritability

Heritability (denoted h2) of a trait is a mathematical estimate of the extent to which variation among individuals can be attributed to their differing genes; it can range from 0 to 1.


Identical twins reared together .86Fraternal twins reared together .60Siblings reared together .47

(Bouchard & McGue, 1981)

Group Differences

A trait can be found to be substantially heritable, but this does not imply that group differences, such as those between men and women, are heritable.

Group Differences


Behavioral Genetics

The New Frontier: Molecular Genetics

The goal of molecular genetics is to identify specific genes that influence behavior.

The APOE4 gene has been linked to Alzheimer’s Disease, which both Ronald Reagan and Charlton Heston developed.

Credit: White House Photo Office

The ACTN3 gene has been linked to high-level success in sprinting

The sample included 107 athletes from short-distance events in track, swimming, cycling, and skating, as well as nine judo athletes. Compared to 18 percent of control subjects, only 6 percent of these athletes—and none of the thirty-two Olympians in the sample—had a variant of ACTN3 that made them alpha-actinin-3 deficient.


Evolutionary Psychology

By virtue of a common ancestralhistory, how are humans alike?

Charles Darwin

From collection of Henry Maull and John Fox

Natural selection: Organisms’ varied offspring compete for survival. Certain behavioral characteristics increase odds of survival in a particular environment. Offspring that survive reproduce and pass on their genes.

Over a 40 year span, Dmitry Belyaev and colleagues in Russian produced a breed of foxes that are “docile, eager to please, and unmistakably domesticated.”

Over a 40 year span, Dmitry Belyaev and colleagues in Russian produced a breed of foxes that are “docile, eager to please, and unmistakably domesticated.”

http://www.youtube.com/watch_popup?v=GjqkBcZLwVY&vq=medium

http://www.youtube.com/watch_popup?v=GjqkBcZLwVY&vq=medium

Evolutionary psychologists believe our tendencies as humans have been shaped by evolution. For example, some women’s experience of nausea in the first three months of pregnancy predisposes them to avoid foods that may be toxic to the fetus.

Credit: Tom Adriaenssen

Gender Differences in Sexuality

Have different adaptive challenge for men and women led to gender differences in psychological functioning?

The Meeting Place, Paul Day

Credit: Oxyman


Evolutionary psychologists believe the answer is yes. Men are responsible for spreading genes, and across cultures, they are found to be more likely to initiate sex than women, and to desire and think about sex more than women.

The Meeting Place, Paul Day

Credit: Oxyman


Also, across cultures, men judge women as more attractive if they have a youthful appearance. According to evolutionary psychologists, this is because young women have a better chance of conceiving than older women.


In the present experiments, male and female confederates of average attractiveness approached potential partners (opposite sex) with 1 of 3 requests: “I have been noticing you around campus. I find you to be very attractive…

"Would you go out tonight?"

"Will you come over to my apartment?"

"Would you go to bed with me?"


Type of Request

Confederate - Subject Date Apt. Bed

Male asking Female

Female asking Male


Type of Request


Male asking Female 56%

Female asking Male 50%


Type of Request


Male asking Female 56% 6%

Female asking Male 50% 69%


Type of Request


Male asking Female 56% 6% 0%

Female asking Male 50% 69% 75%


In general, the female experimenters reported that men were at ease with the request. They would say “Why do we have to wait until tonight?” or “I cannot tonight, but tomorrow would be fine.”…In contrast, the women’s response…was “You’ve got to be kidding,” or “What is wrong with you? Leave me alone.”


Type of Request


Male asking Female 50% 0% 0%

Female asking Male 50% 69% 69%

(1982 Replication)


Parents and Peers

Parents and Early Experiences

Whether early environment is impoverished or enriched has a major impact on brain development: Rosenzweig and Krech found that rats raised in an enriched environment developed a larger, and thicker, cortex than rats raised in an impoverished environment.

Experience and Brain Development

A trained brain: A well-learned finger-tapping task, practiced thousands of times, activates more motor cortex neurons (in orange) than were active in the same brain before training.


This same sort of brain plasticity is seen in humans. In one study, researchers found that London taxi cab drivers had larger hippocampal brain regions responsible for spatial memory than did controls.

Credit: Andreas Tusche


How Much Credit (or Blame) Do Parents Deserve?

Parents do matter, especially at extremes. For example, abused children are prone to abuse their own children as adults. Somewhat surprisingly, however, shared environmental influences on personality and intelligence are fairly small (around 10%).

How Much Credit (or Blame) Do Peers Deserve?

There are large influences of peers on a variety of behaviors and traits. Psychologist Judith Rich Harris concludes that peers play a larger role in shaping personality than do parents. Credit: Ole Graf/zefa/Corbis


Cultural Influences

Culture: Behavior, ideas, attitudes, values and traditions shared by a group transmitted from one generation to the next

Many other animals are social. However, nearly all other animals lack the means to preserve innovations, and in so doing, to build a culture. What separates humans from all other animals is mastery of language.

Credit: Bart Swanson

Wolves, for example, are social animals, and yet they function almost exactly as they did 10,000 years ago. By contrast, on an ever day basis, you and I use technologies that were unimaginable only a century ago. Credit: HawaiianMama


Cultural Influences

Variation Across Cultures

Each cultural group has norms—rules for expected and accepted behavior. For example, cultures differ in norms regarding personal space—the portable buffer zone we like to maintain around our bodies. North Americans tend to prefer more personal space than do Latin Americans.

Credit: GodShiru

And when our personal space is invaded, we feel uncomfortable. Lyndon Johnson was known to be a “close talker,” perhaps as a means of intimidation. At left, Senator Richard Russell receiving the “Johnson treatment.”Credit: Yoichi R. Okamoto

https://www.youtube.com/watch?v=NGVSIkEi3mM

https://www.youtube.com/watch?v=NGVSIkEi3mM


Cultural Influences

Variation Over Time

As case in point, consider cultural changes in the United States since the 1960s. Some changes are positive. Women are more likely to marry for love than out of economic need, and rights of minority groups have expanded. But some are negative. There is more divorce, delinquency, and depression.


Cultural Influences

Culture and the Self

Cultures vary in the extent to which they give priority to the expression of personal identity or group identity. Cultures that give priority to the independent self are high in individualism, while those that give priority to the interdependent self are high in collectivism.

Credit: Kevin R. Morris

Differences in individualism vs. collectivism influence how we make attributions about our success and failures.

Credit: Martin Dougiamas

The boarding school model of child-rearing

Differences in individualism vs. collectivism also have an influence on child-rearing. Many Asians and Africans live in cultures that greatly value emotional closeness, whereas Westerners place a greater emphasis on development of independence.


Gender Development

Gender Similarities and Dissimilarities

Much is made about differences between males and females in the popular press, and there are some striking differences. Women have a keener sense of smell than men, and are twice as vulnerable as men to depression and anxiety. And girls tend to be more cooperative and less competitive in their play than boys.

On the other hand, men are more prone to physical aggression than women (the male-to-female arrest ratio in the United States is 10 to 1), and are more dominant, forceful, and independent than women.

However, some of the most talked about gender differences are actually quite small. For example, the average difference between females and males in self-esteem is only about .2 standard deviations.

And other much talked-about gender differences are not substantiated by scientific evidence. For example, despite the popular belief otherwise, there appears to be no evidence that women are better at multitasking than men.

Credit: Jagger


We are the product of nature and nurture. Genes are all-pervasive but not all-powerful. Culture is all-pervasive but not all-powerful.

Chapter Review

What does the subfield of behavioral genetics focus on?

What do evolutionary psychologists study?

What is known about peer versus parent influences on traits?

What is known about gender differences and similarities?

Chapter 4 Review

Question(s) from textbook on material not covered in class:

Gene-Environment Interaction (pp. 137-138)

nature, nurture, and human diversity chapter 4

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