1.1 Interaction of Heredity and Environment

Nature and Nurture Work Together

Behavior arises from the interaction of heredity (nature) and environment (nurture). Genes provide a blueprint, but experiences shape how genes are expressed. Psychologists study twins and adopted individuals to separate genetic and environmental influences, since identical twins share 100% of genes while environments can differ.

Behavior Genetics Key Terms

Behavior genetics examines how heredity and environment influence behavior. Heritability is the proportion of variation in a trait within a population attributable to genes, not a fixed percentage for individuals. Epigenetics studies how environmental factors (stress, toxins) turn genes on or off without changing DNA sequence, affecting expression across generations.

Evolutionary Perspective

Evolutionary psychology explains behaviors as products of natural selection—traits that increased survival and reproduction became more common. This perspective highlights universal human behaviors (like fear responses) as adaptive, while acknowledging culture and learning still modify how these predispositions are expressed.

Key terms

Behavior genetics

The study of how heredity and environment influence behavior.

Heritability

The proportion of variation in a trait within a population attributed to genetic differences.

Epigenetics

Study of how environmental factors switch genes on or off without changing the DNA sequence.

Evolutionary psychology

Explains behaviors as products of natural selection that increased survival and reproduction.

Twin studies

Research comparing identical and fraternal twins to separate genetic from environmental influences on behavior.

Try an AP-style question

What does this most strongly suggest?

1. Shared homes matter more than genes
2. IQ can't be measured reliably
3. Environment has no effect on IQ
4. Genes substantially influence IQ