Behavior Genetics Chapter 4, Lecture 1 “Genes and environment – nature and nurture – work together like two hands clapping.” - David Myers

Behavior Genetics: Predicting Individual Differences Behavior Geneticists study our differences and weigh the relative effects of heredity and environment.

Chromosomes containing DNA (deoxyribonucleic acid) are situated in the nucleus of a cell. Genes: Our Codes for Life

Segments within DNA consist of genes that make proteins to determine our development.

Genome Genome is the set of complete instructions for making an organism, containing all the genes in that organism. Thus, the human genome makes us human, and the genome for drosophila makes it a common house fly. Now pair up with someone you don’t know well and take a look at handout 4-2

Twin and Adoption Studies Studying the effects of heredity and environment on two sets of twins, identical and fraternal, has come in handy.

Separated Twins A number of studies compared identical twins reared separately from birth, or close thereafter, and found numerous similarities. Separated Twins Personality, Intelligence Abilities, Attitudes Interests, Fears Brain Waves, Heart Rate

Separated Twins Critics of separated twin studies note that such similarities can be found between strangers. Researchers point out that differences between fraternal twins are greater than identical twins. Bob Sacha

Biological Versus Adoptive Relatives Adoption studies, as opposed to twin studies, suggest that adoptees (who may be biologically unrelated) tend to be different from their adoptive parents and siblings.

Adoptive Studies Adoptive studies strongly point to the simple fact that biologically related children turn out to be different in a family. So investigators ask: Do siblings have differing experiences? Do siblings, despite sharing half of their genes, have different combinations of the other half of their genes? Ultimate question: Does parenting have an effect?

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

Temperament and Heredity Temperament refers to a person’s stable emotional reactivity and intensity. Identical twins express similar temperaments, suggesting heredity predisposes temperament.

Nature and Nurture Some human traits are fixed, such as having two eyes. However, most psychological traits are liable to change with environmental experience. Genes provide choices for the organism to change its form or traits when environmental variables change. Therefore, genes are pliable or self-regulating.

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.

Heritability: the proportion of variation among individuals that we can attribute to genes. The heritability of a trait may vary, depending on the range of populations and environments studied.

Gene-Environment Interaction Genes and environment affect our traits individually, but more important are their interactive effects. People respond differently to Rowan Atkinson (Mr. Bean) than Orlando bloom. Rex Features Alessia Pierdomenico /Reuters/Corbis

Other interesting examples of gene- environment interaction: Girls raised in fatherless households experience puberty earlier. “Apparently the change in timing,” writes Matt Ridley, “is the reaction of a still mysterious set of genes to their environment. Scientists don’t know how many sets of genes act in this way.” Fear of snakes, the most common human phobia, seems instinctive. Still, studies with monkeys indicate that their fear of snakes (and most likely ours) must be acquired by watching another individual react with fear to snakes. We inherit not a fear of snakes but a genetic predisposition to learn a fear of snakes.

Other interesting examples of gene- environment interaction: In contrast to chimpanzees, people have the capacity for complex, grammatical language. However, language must be learned from other language-speaking human beings. The capacity to learn is shaped by genes that open and close a critical window when learning can take place. If children are not exposed to spoken language during this critical period, they will always struggle with speech.

Other interesting examples of gene- environment interaction: Ray Blanchard’s research at the University of Toronto indicates that gay men are more likely than either lesbians or heterosexual men to have older brothers (but not older sisters). Apparently, something about occupying the womb that has held other boys occasionally leads to reduced birth weight, a larger placenta, and increased likelihood of homosexuality. Blanchard suspects that an immune reaction in the mother grows stronger with each male pregnancy. This immune response may affect the expression of key genes during brain development that increases a boy’s attraction to his own sex. The explanation obviously does not hold true for all cases of homosexuality, but it may provide important clues into the origin of heterosexual as well as homosexual orientation for some people.

Other interesting examples of gene- environment interaction: Evidence suggests that childhood maltreatment may produce an antisocial adult. However, Terrie Moffitt, in New Zealand studies, finds that this may be true for only a genetic minority. In fact, those with high-active monoamine oxidase A (MOA) genes are virtually immune to the effects of maltreatment; that is, they do not become more antisocial. Those with low-active genes are much more antisocial if maltreated, yet slightly less antisocial if not maltreated. In short, maltreatment along does not produce antisocial behavior; the low-active gene must also be present. Similarly, the low-active gene alone does not produce antisocial behavior; maltreatment must also occur.

Homework Read p “A visitor from outer space could drop in anywhere and find humans dancing and feasting, singing and worshiping, playing sports and games, laughing and crying, living in families and forming groups.” - David Myers