Chapter 4 Nature, Nurture, And Human Diversity

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4-1: What are genes, and how do behavior geneticists explain our individual differences?

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Genes are the biochemical units of heredity that make up chromosomes, the threadlike coils of DNA. When genes are "turned on" (expressed), they provide the code for creating the proteins that form our body's building blocks. Most human traits are influenced by many genes acting together.

Behavior geneticists seek to quantify genetic and environmental influences on our traits, in part through studies of identical (monozygotic) twins, fraternal (dizygotic) twins, and adoptive families. Shared family environments have little effect on personality, and the stability of temperament suggests a genetic predisposition.

Front 2

4-2: What is the promise of molecular genetics research?

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Molecular geneticists study the molecular structure and function of genes, including those that affect behavior. Psychologists and molecular geneticists are cooperating to identify specific genes—or more often, teams of genes—that put people at risk for disorders.

Front 3

4-3: What is heritability, and how does it relate to individuals and groups?

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Heritability describes the extent to which variation among members of a group can be attributed to genes. Heritable individual differences (in traits such as height or intelligence) do not necessarily imply heritable group differences. Genes mostly explain why some people are taller than others, but not why people are taller today than they were a century ago.

Front 4

4-4: How do heredity and environment work together?

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Our genetic predispositions and our surrounding environments interact. Environments can trigger gene activity, and genetically influenced traits can evoke responses from others. The field of epigenetics studies the influences on gene expression that occur without changes in DNA.

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4-5: How do evolutionary psychologists use natural selection to explain behavior tendencies?

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Evolutionary psychologists seek to understand how our traits and behavior tendencies are shaped by natural selection, as genetic variations increasing the odds of reproducing and surviving are most likely to be passed on to future generations. Some variations arise from mutations (random errors in gene replication), others from new gene combinations at conception. Humans share a genetic legacy and are predisposed to behave in ways that promoted our ancestors' surviving and reproducing. Charles Darwin's theory of evolution is an organizing principle in biology. He anticipated today's application of evolutionary principles in psychology.

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4-6: How might an evolutionary psychologist explain gender differences in sexuality and mating preferences?

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Men tend to have a recreational view of sexual activity; women tend to have a relational view. Evolutionary psychologists reason that men's attraction to multiple healthy, fertile-appearing partners increases their chances of spreading their genes widely. Because women incubate and nurse babies, they increase their own and their children's chances of survival by searching for mates with the potential for long-term investment in their joint offspring.

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4-7: What are the key criticisms of evolutionary psychology?

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Critics argue that evolutionary psychologists (1) start with an effect and work backward to an explanation, (2) do not recognize social and cultural influences, and (3) absolve people from taking responsibility for their sexual behavior. Evolutionary psychologists respond that understanding our predispositions can help us overcome them. They also cite the value of testable predictions based on evolutionary principles, as well as the coherence and explanatory power of those principles.

Front 8

4-8: How do early experiences modify the brain?

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As a child's brain develops, neural connections grow more numerous and complex. Experiences then trigger a pruning process, in which unused connections weaken and heavily used ones strengthen. Early childhood is an important period for shaping the brain, but throughout our lives our brain modifies itself in response to our learning.

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4-9: In what ways do parents and peers shape children's development?

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Parents influence their children in areas such as manners and political and religious beliefs, but not in other areas, such as personality. As children attempt to fit in with their peers, they tend to adopt their culture—styles, accents, slang, attitudes. By choosing their children's neighborhoods and schools, parents exert some influence over peer group culture.

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4-10: How do cultural norms affect our behavior?

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A culture is a set of behaviors, ideas, attitudes, values, and traditions shared by a group and transmitted from one generation to the next. Cultural norms are understood rules that inform members of a culture about accepted and expected behaviors. Cultures differ across time and space.

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4-11: How do individualist and collectivist cultures influence people?

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Within any culture, the degree of individualism or collectivism varies from person to person. Cultures based on self-reliant individualism, like those found in North America and Western Europe, tend to value personal independence and individual achievement. They define identity in terms of self-esteem, personal goals and attributes, and personal rights and liberties. Cultures based on socially connected collectivism, like those in many parts of Asia and Africa, tend to value interdependence, tradition, and harmony, and they define identity in terms of group goals, commitments, and belonging to one's group.

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4-12: What are some ways in which males and females tend to be alike and to differ?

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Gender refers to the characteristics, whether biologically or socially influenced, by which people define male and female. We are more alike than different, thanks to our similar genetic makeup—we see, hear, learn, and remember similarly. Males and females do differ in body fat, muscle, height, age of onset of puberty, and life expectancy; in vulnerability to certain disorders; and in aggression, social power, and social connectedness.

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4-13: How is our biological sex determined, and how do sex hormones influence gender development?

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Biological sex is determined by the father's contribution to the twenty-third pair of chromosomes. The mother always contributes an X chromosome. The father may also contribute an X chromosome, producing a female, or a Y chromosome, producing a male by triggering additional testosterone release and the development of male sex organs. Sex-related genes and physiology influence behavioral and cognitive gender differences between males and females.

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4-14: How do gender roles and gender typing influence gender development?

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Gender roles, the behaviors a culture expects from its males and females, vary across place and time. Social learning theory proposes that we learn gender identity—our sense of being male or female—as we learn other things: through reinforcement, punishment, and observation. Critics argue that cognition also plays a role because modeling and rewards cannot explain gender typing. Transgender people's gender identity or expression differs from their birth sex.

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4-15: What is included in the biopsychosocial approach to development?

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Individual development results from the interaction of biological, psychological, and social-cultural influences. Biological influences include our shared human genome; individual variations; prenatal environment; and sex-related genes, hormones, and physiology. Psychological influences include gene-environment interactions; the effect of early experiences on neural networks; responses evoked by our own characteristics, such as gender and temperament; and personal beliefs, feelings, and expectations. Social-cultural influences include parental and peer influences; cultural traditions and values; and cultural gender norms.