Chapter 4 Nature, Nurture, and Human Diversity

Chapter 4 Nature, Nurture, and Human Diversity

Behavior Genetics: Predicting Individual Differences The topics in the text: 1.genes 2.twin and adoption studies 3.temperament and heredity 4.gene/environment interaction Behavior geneticists study how heredity and environment contribute to human differences. Let s start by looking at GENES.

GENES: The Building Blocks of Heredity and Development Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells. Chromosome: threadlike structure made largely of DNA molecules DNA: a spiraling, complex molecule containing genes DNA (Deoxyribonucleic Acid)

Chromosomes and Inheritance The human genome includes 46 chromosomes in 23 sets matched sets; each chromosome has the same gene locations. This includes the X and Y chromosomes, not a matched set in males, who are missing some genes on the Y. A biological parent donates half his/her set of chromosomes to his/her offspring. We received half a set of chromosomes from each biological parent. The genome: an organism s entire collection of genes

Genes are not blueprints; they are molecules that have the ability to direct the assembly of proteins that build the body. This genetic protein assembly can be turned on and off by the environment, gene expression, or by other genes. Any trait we see is a result of the complex interactions of many genes and countless other molecules. How Genes Work

Fraternal and Identical Twins Fraternal twins from separate eggs are not any more genetically alike than other siblings. Identical twin: Same sex only Fraternal twin: Same or opposite sex Twin and Adoption Studies To assess the impact of nature and nurture, how do we examine how genes make a difference within the same environment? study traits of siblings vs. identical twins see if the siblings vary more than twins

Identical vs. Fraternal Twins Studies of twins in adulthood show that identical twins are more alike than fraternal twins in: personality traits such as extraversion (sociability) and neuroticism (emotional instability). behaviors/outcomes such as the rate of divorce. abilities such as overall Intelligence test scores. Twin and Adoption Studies How do we find out how the same genes express themselves in different environments? We can study the traits of identical twins as they grow up, or if they were raised separately (e.g., the Minnesota Twin Family Study).

Studies of Identical Twins Raised Apart Similarities found in identical twins despite being raised in different homes: personality, styles of thinking and relating abilities/intelligence test scores attitudes interests, tastes specific fears brain waves, heart rate Given the evidence of genetic impact on how a person turns out, does parenting/nurture make any difference? Does the home environment have any impact? Studies have been performed with adopted children for whom the biological relatives are known. Findings: Adopted children seem to be more similar to their genetic relatives than their environmental/nurture relatives.

Searching for Parenting Effects: Biological vs. Adoptive Relatives Despite the strong impact of genetics on personality, parenting has an influence on: religious beliefs values manners attitudes politics habits

Temperament is another difference not caused by parenting. From infancy into adulthood, most people do not seem to change temperament (defined as a person s general level and style of emotional reactivity). According to some researchers, three general types of temperament appear in infancy: easy difficult slow to warm up

Nature and nurture working together Interaction of Genes and Environment Self-regulation: genes turn each other on and off in response to environmental conditions Epigenetics: the environment acts on the surface of genes to alter their activity Example of selfregulation in animals: shortened daylight triggers animals to change fur color or to hibernate Example of selfregulation in humans: obesity in adults can turn off weight regulation genes in offspring

Evolutionary Psychology: Understanding Human Nature Some topics: Natural selection and adaptation Evolutionary success may help explain similarities An evolutionary explanation of human sexuality Evolutionary psychology is the study of how evolutionary principles help explain the origin and function of the human mind, traits, and behaviors. We have been talking so far about human differences; we may now seek insight in the ways in which humans are alike. 14

Evolutionary Psychology: Natural Selection: How it Works Begin with a species genome, which contains a variety of versions of genes that shape traits. Conditions make it difficult for individuals with some traits (some versions of those genes) to survive long enough to reproduce. Other individuals thus have their traits and genes selected to spread in the population.

Artificial Selection The Domesticated Silver Foxes Dmitri Balyaev and Lyudmila Trut spent 40 years selecting the most gentle, friendly, and tame foxes from a fox population, and having those reproduce. As a result, they were able to shape avoidant and aggressive creatures into social ones, just as wolves were once shaped into dogs. 16

How might evolution have shaped the human species? Example: Why does stranger anxiety develop between the ages of 9 and 13 months? Hint: in evolutionary/survival terms, humans are learning to walk at that time. Possible explanation: infants who used their new ability to walk by walking away from family and toward a lion might not have survived to reproduce as well as those who decided to cling to parents around the time they learned to walk. 17

Evolutionary Psychology s Explanation of Phobias Why do people so easily acquire a phobia of snakes? An evolutionary psychologist would note that snakes are often poisonous so those who more readily learned to fear them were more likely to survive and reproduce. Can we apply the same logic to phobias about heights? enclosed spaces? clowns? 18

Male and Female Differences: Focusing on Mating Preferences First issue: quantity (of mating) Generally, men think more than women about sex, and men are more likely to think that casual sex is acceptable. Why might natural selection have resulted in greater male promiscuity? An evolutionary psychologist s answer: Men who had the trait of promiscuity were more likely to have their genes continue, and even spread, in the next generation. And there is little cost to spreading extra genes. For women, a trait of promiscuity would not greatly increase the number of babies, and it would have greater survival costs (pregnancy, once a life-threatening condition).

Possible Evolutionary Strategies in Seeking Partners Q: How would evolutionary psychology explain why males and females have different preferences for sexual partners? Men seek women with a fuller figure to make sure they are not too young or too old to have children? Women seek males with loyal behavior and physical/social power and resources in order to ensure the survival of the mother s offspring?

Nature/Nurture From Genes to the Role of Environment Experience and Brain Development Rats living in an enriched environment (more social interaction and physical play) experienced a greater growth in brain size and complexity than those rats living in an impoverished environment.

Impact of Experience/Nurture on Brain Development The Process Continues into Adulthood Repeated practice at a finger-tapping task begins to activate a [slightly] larger group of motor neurons.

Is parenting a powerful environmental influence on development? Generally, environmental influences, including parenting, account for about 10 percent of temperament, although a much higher percentage for other features such as values. Non-abusive average parents should ease off on both the blame and the credit they assume for how their kids turn out. Where this percentage increases: extreme parenting, including severe neglect and abuse

Peer Influence The degree of peer influence is hard to trace. Apparent conformity (the whole group smokes) could be a selection effect (they get together because they want to be with others who like to smoke). Interaction with peers can teach new social skills. Parents may try to have indirect influence by selecting a child s peers, such as by selecting a school or neighborhood. However, ultimately, most children self-select their peers.

Parents vs. Peers Battling over non-genetic influence Parents have more influence on: Peers have more influence on: Education and career path Cooperation Self-discipline Responsibility Charitableness Religion Style of interaction with authority figures Learning cooperation skills Learning the path to popularity Choice of music and other recreation Choice of clothing and other cultural choices Good and bad habits

Culture Influences on Development Culture and the self: individualism and collectivism Individualist cultures value independence. They promote personal ideals, strengths, and goals, pursued in competition with others, leading to individual achievement and finding a unique identity. Collectivist cultures value interdependence. They promote group and societal goals and duties, and blending in with group identity, with achievement attributed to mutual support. Individualist and Collectivist Cultures Compared

Child-rearing: Cultural Differences People in individualist cultures might raise children to be self-reliant and independent. People in collectivist cultures might raise children to be compliant, obedient, and integrated into webs of mutual support. People in Asian and African cultures might raise children to be more emotionally and physically close to others than in western European cultures.

Differences Between Genders Biological: women enter puberty earlier, live longer, and have more fat and less muscle Mental and Behavioral Health: women are more likely to have depression, anxiety, or eating disorders men are more likely to have autism, ADHD, and antisocial personality disorder Gender and Aggression: men behave more aggressively than women, and are more likely to behave in ways that harm others this difference applies to physical aggression rather than verbal or relational aggression

Gender and Social Connection: Play When boys play, the focus tends to be on the activity. Male play is more competitive. Men tend to dictate how the playtime will proceed. When women play, the focus tends to be on connection and conversation. Female play is more social. Girls tend to invite feedback. Are these differences due to nature or nurture?

Gender and Social Communication Women communicate more than men: more time with friends more text messages longer phone calls However, men and women speak about the same number of words per day. What fills in the extra time on those longer phone calls? Maybe. listening? Men and women use communication differently. Men state their opinions and solutions. Men speak about things and actions. Women seek input and explore relationships. Women speak about people and feelings.

Gender and Social Connectedness Both men and women turn to women when they want someone to talk to, seeking the tend and befriend response or better listening. In general, women change roommates more often. Women tend to have stronger ties to friends and family. Women are often more involved with religion.

The Biology of Gender What biologically makes us male or female? It begins with whether our 23rd pair of chromosomes looks like XX (female) or Xy (male). Testes develop, and at seven weeks, the testes produce a flood of testosterone. Hormones then guide the development of external sex organs. Brain Differences During the fourth and fifth month of pregnancy, sex hormones bathe the fetal brain. In adulthood, women have thicker areas in a part of the frontal lobes that help with verbal fluency. There are also differences in the amygdala, hippocampus, and ratio of cell bodies to axons.

Lessons about Gender: Unusual Biological Cases In cases in which prenatal testosterone levels were high in females, there is an increase in tomboyish behavior, possibly caused by other people s response to more masculine features. However, there is not a general pattern of gender identity change. In cases where males had underformed or absent genitalia, attempts to raise them as females generally did not work out well. Breaking Free of Gender Transgendered people have a sense of sexual identity that is different from their birth sex. Transsexual people act on this sense of difference by living as a member of the opposite sex, often with hormonal and surgical interventions that support this gender reassignment.

Change in Social Roles? If current trends continue, women will soon be the majority of practitioners in some fields that were once dominated by men in the United States.

Culture Influence on Gender Role Development Or is it instinct? Social learning theory: we learn gender role behavior by imitation, and by rewards and punishments that shape our behavior Gender schemas: the cognitive frameworks for developing concepts of male and female ; these frameworks guide our observations Gender typing: the instinct which drives some children to fit into traditional gender roles

Influences on Who You ve Become

Beyond Biopsychosocial Influences: CHOICE Is our behavior and identity rigidly determined by our combination of nature/genes and nurture/experience? Even if free will is an illusion, it would seem that we can make choices that override our genetic influences, that differ from cultural norms, and that do not fit our environment. We can even choose to directly alter culture, environment, and even genes.