Module 14 Behavior Genetics: Predicting Individual Differences

LEARNING TARGETS

• 14-1 Define chromosomes, DNA, genes, and the human genome, and describe how behavior geneticists explain our individual differences.
• 14-2 Explain how twin and adoption studies help us understand the effects and interactions of nature and nurture.
• 14-3 Explain what is meant by heritability and discuss how it relates to individuals and groups.
• 14-4 Describe how molecular genetics research is changing our understanding of the effects of nature and nurture.

What makes you you? In important ways, we are each unique. We are each a one-of-a-kind package of looks, language, personality, interests, and cultural background.

We are also the leaves of one tree. Our human family shares not only a common biological heritage—cut us and we bleed—but also common behavioral tendencies. Our shared brain architecture disposes us to sense the world, develop language, and feel hunger through identical mechanisms. Whether we live in the Arctic or the tropics, we prefer sweet tastes to sour. We divide the color spectrum into similar colors. And we feel drawn to behaviors that produce and protect offspring.

Our kinship also appears in our social behaviors. Whether named Gonzales, Nkomo, Ahmadi, Smith, or Wong, we start fearing strangers at about 8 months, and as adults we prefer the company of those with attitudes and attributes similar to our own. Coming from different parts of the globe, we know how to read one another’s smiles and frowns. As members of one species, we affiliate, conform, return favors, punish offenses, organize hierarchies of status, and anguish over a child’s death. 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. Taken together, such universal behaviors define our human nature.

What causes our striking diversity, and also our shared human nature? How much are our differences shaped by our differing genes? And how much by our environment—by every external influence, from maternal nutrition while in the womb to social support while nearing the tomb? To what extent are we formed by our upbringing? By our culture? By our current circumstances? By people’s reactions to our genetic dispositions? By our own choices and efforts? This module and the next begin to tell the scientific story of how our genes (nature) and environments (nurture) together knit us.