Download Behavior Genetics and Evolutionary Psychology

Behavior Genetics and
Evolutionary Psychology
Members of the human family share common behavioral tendencies but are also strikingly diverse.
To what extent are we shaped by our heredity and to what degree by our life history? The conclusions—that nature is crucially important and that nurture is crucially important—are central to
today’s psychology.
Genes provide the blueprints that design both our universal human attributes and our individual traits. Behavior geneticists explore individual differences. By using twin, adoption, and temperament studies, they assess the heritability of various traits and disorders. Their research indicates that both nature and nurture influence our life courses. We are products of interactions
between our genetic predispositions and our surrounding environments. Molecular geneticists
search for genes that put people at risk for genetically influenced disorders, which has potential
benefits as well as risks.
Evolutionary psychologists focus on what makes us alike as humans. They study how natural
selection favored behavioral tendencies that contributed to the survival and spread of our genes.
For example, in explaining gender differences in sexual behavior, they argue that women most
often send their genes into the future by pairing wisely, men by pairing widely. Critics maintain
that evolutionary psychologists make too many hindsight explanations and underestimate the role
of culture.
➤ Introductory Exercise: Fact or Falsehood?
➤ Lecture: Universal People
11-1. Give examples of differences and similarities within the human family, noting how they are shaped
by our genes and our environment.
Members of the human family differ in personality, interests, culture, and family background. At
the same time, our shared brain architecture predisposes us to sense the world, develop language,
and experience hunger through the same mechanisms. Humans everywhere affiliate, conform,
reciprocate favors, punish offenses, and grieve a child’s death. Our genes and our environment contribute to our striking diversity and shared human nature.
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Module 11 Behavior Genetics and Evolutionary Psychology
Behavior Genetics: Predicting Individual Differences
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Lectures: The Origins of Blue Eyes; The Genetic Revolution
Exercise: Genetic Factors
Exercise/Project: Genetic Influences
Instructor Video Tool Kit: Ethics in Human Research: Violating One’s Privacy
11-2. Identify the types of questions that interest behavior geneticists, and describe the elements of
heredity: chromosome, DNA, genes, and genome.
Behavior geneticists study our differences and aim to determine the relative importance of heredity and environment on behavior. Environment includes every nongenetic influence, from prenatal
nutrition to the people and things around us.
Every cell nucleus contains the genetic master code for the body. Within each cell are 46 chromosomes with 23 donated by each parent. Each chromosome is composed of a coiled chain of a molecule, called DNA (deoxyribonucleic acid). Genes are DNA segments that, when “turned on”
(active or expressed), provide the code for the production of protein molecules. By directing the
manufacture of proteins, the approximately 30,000 genes that compose the human body determine
our physical development. The genome provides the complete instructions for making an organism, consisting of all the genetic material in the organism’s chromosomes. Variations at particular
gene sites in the DNA define each person’s uniqueness. Human traits are influenced by many
genes interacting with the environment.
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Lectures: The Minnesota Twin Study; “Mom Always Liked You Best”
Exercise: Striking Similarities
Videos: Module 16 of The Mind series, 2nd ed.: The Effect of Aging on Cognitive Functioning: Nature/Nurture
Instructor Video Tool Kit: Nature Versus Nurture: Growing up Apart
11-3. Describe how twin and adoption studies help us differentiate hereditary and environmental
influences on human behavior.
Comparisons of identical twins, who are genetic clones, and fraternal twins, who develop from
separate eggs, help behavior geneticists tease apart the effects of heredity and environment. On
both extraversion and neuroticism, identical twins are much more similar than fraternal twins. The
discovery that identical twins separated at birth show remarkable similarities also suggests genetic
influence. Indeed, separated fraternal twins do not exhibit similarities comparable to those of separated identical twins. However, shared genes can translate into shared experiences.
Adoption studies enable comparisons with both genetic and environmental relatives. Adoptees’
traits bear more similarities to their biological parents than to their caregiving adoptive parents.
Nonetheless, the latter do influence their children’s attitudes, values, manners, faith, and politics.
Clearly, nature and nurture shape one’s developing personality.
➤ Exercise: EAS Temperament Survey
➤ Video: Segment 23 of the Scientific American Frontiers series, 2nd ed.: Bringing up Monkey
11-4. Discuss how the relative stability of our temperament illustrates the influence of heredity on
development.
An infant’s temperament is his or her characteristic emotional excitability and intensity. From the
first weeks of life, some babies are more relaxed and cheerful, while others are difficult (more
tense and irritable). Still others are slow to warm up. These differences in temperament tend to
endure. For example, the most emotionally intense preschoolers tend to be relatively intense young
adults. Compared with fraternal twins, identical twins have more similar temperaments, indicating
that heredity may predispose temperament differences.
➤ Lectures: Genetic Influences on Psychological Traits; Nature and Nurture; Gene-Environment Correlation
➤ Feature Film: Fly Away Home and Imprinting
➤ ActivePsych: Scientific American Frontiers, 3rd ed.: Genes and Personality: Understanding Williams Syndrome
Module 11 Behavior Genetics and Evolutionary Psychology
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➤ Instructor Video Tool Kit: 100-Years-Old and Counting: Psychological and Biological Factors; Genes and
Personality
11-5. Explain what is meant by heritability, and give examples of the interaction of gene and environment on specific traits.
Heritability describes the extent to which variation among members of a group can be attributed
to genes. If the heritability of intelligence is 50 percent, this does not mean that one’s intelligence
is 50 percent genetic. Instead, it means that we can attribute to genetic influence 50 percent of the
observed variation among people.
Our genes affect how our environment reacts to and influences us. Nature enables nurture.
Because of human adaptability, most psychologically interesting traits are expressed in particular
environments. In other words, genes are self-regulating; they can react differently in different environments.
We are all the products of interactions between our genetic predispositions and our surrounding
environments. For example, a stressful environment can trigger genes that affect the production of
neurotransmitters that underlie depression. Breastfeeding boosts later intelligence only for the 90
percent of infants with a gene that assists in breaking down fatty acids present in human milk.
Similarly, a baby who is genetically predisposed to be social and easy going may, in contrast to
one who is less so, attract more affectionate and stimulating care and thus develop into a warmer
and more outgoing person.
➤ Lecture: Designer Babies?
➤ Videos: Module 12 of The Brain series, 2nd ed.: Huntington’s Disease; Segment 22 of the Scientific American
Frontiers series, 2nd ed.: Bypass Genes
➤ Instructor Video Tool Kit: Designer Babies
➤ Feature Film: Gattaca and “Designer Babies”
11-6. Identify the potential uses of molecular genetics research.
Molecular geneticists study the molecular structure and function of genes. They seek to identify
specific genes influencing behavior. In labs worldwide, molecular geneticists are teaming with
psychologists to identify genes that put people at risk for genetically influenced disorders.
Potentially, steps may be taken to prevent problems before they happen. With this benefit, however,
also comes risks of labeling people in ways that may lead to discrimination. Prenatal screening
poses hopeful possibilities but also difficult problems as parents become able to select their children’s traits. In China and India, where boys are highly valued, testing for an offspring’s sex has
enabled selective abortions. Millions of parents will select for health and perhaps for brains and
beauty. However, by “selecting” out certain traits, we may deprive ourselves of future Handels, van
Goghs, Lincolns, and Dickinsons, who were all troubled people.
Evolutionary Psychology: Understanding Human Nature
➤ Lectures: Evolutionary Psychology; Misunderstanding Evolutionary Theory and Psychology
➤ Exercises: Evolutionary Psychology; Darwinian Grandparenting
➤ PsychSim 5: Mind-Reading Monkeys
➤ Instructor Video Tool Kit: The Nature-Nurture Issue
11-7. Describe the area of psychology that interests evolutionary psychologists, and point out some possible effects of natural selection in the development of human characteristics.
Evolutionary psychologists focus on what makes us so much alike as humans. They study how
natural selection has shaped our universal behavioral tendencies.
Natural selection is the principle that, among the range of inherited trait variations, those that lead
to increased reproduction and survival will most likely be passed on to succeeding generations.
Nature selects beneficial variations from among the mutations (random errors in gene replication)
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Module 11 Behavior Genetics and Evolutionary Psychology
and the new gene combinations produced at each human conception. During human ancestry,
genes that enable today’s capacity to learn and adapt had survival value. Similarly, we love the
taste of fats and sweets, which once were hard to come by but which prepared our ancestors to survive famines. This particular natural disposition is mismatched with today’s junk-food environment.
➤ Lectures: Gender Differences in Sexuality; Evolutionary Theory and Gender Differences in Motivation; Infidelity;
Evolutionary Psychology and the Coolidge Effect
➤ Exercises: Mate Preferences; Hendrick Sexual Attitudes Scale
➤ PsychSim 5: Dating and Mating
➤ Instructor Video Tool Kit: Evolutionary Psychology and Sex Differences; Openness to Casual Sex: A Study of Men
Versus Women
11-8. Identify some gender differences in sexuality and mating preferences, and describe evolutionary
explanations for those differences.
Gender refers to the biologically and socially influenced characteristics by which people define
male and female. One of the largest reported gender differences is women’s greater disapproval of
and lesser willingness to engage in casual, uncommitted sex. In comparison to women, men think
more about sex, masturbate more often, are more likely to initiate sex, and make more sacrifices to
gain sex.
Evolutionary psychologists apply the principle of natural selection to explain women’s more relational and men’s more recreational approaches to sex. Compared with eggs, sperm are cheap.
While a woman usually incubates and nurses one infant at a time, a man can spread his genes by
impregnating other females. Women most often send their genes into the future by pairing wisely,
men by pairing widely. Women increase their own and children’s chances of survival by searching
for mates with economic resources and social status. Being attracted to healthy, fertile-appearing
partners increases men’s chances of spreading their genes widely.
11-9. Summarize the criticisms of evolutionary explanations of human behaviors, and describe the
evolutionary psychologists’ responses to those criticisms.
Critics argue that evolutionary psychologists start with an effect (e.g., gender sexuality difference)
and work backward to propose an explanation. In addition, much of who we are is not hard-wired.
Cultural expectations shape the genders. Still others suggest that evolutionary explanations may
undercut moral responsibility. In response, evolutionary psychologists point to the explanatory
power of their theoretical principles, especially those offering testable predictions. They also note
that understanding our propensities may help us to overcome them.