1. 1.Behavior geneticists study the genetic basis of behavior and personality differences among people. 2.The more closely people are biologically related, the more genes they share. 3.Traits can be monogenic (determined by one gene) or polygenic (determined by several genes). 4.Researchers use heritability to determine how much of a trait’s variation within a population is due to genes.

2. 1.Psychologists use family studies, twin studies, and adoption studies to see whether, and to what extent, characteristics are genetic. 2.Heredity interacts with environment to influence psychological traits.

3. 1.Evolution is the change in the frequency of genes in a population. 2.Charles Darwin proposed the theory of natural selection, which states that inherited characteristics that give an organism a survival or reproductive advantage are passed on more often to future generations than other inherited characteristics. 3.An adaptation is an inherited characteristic that increases in a population because it provides a survival or reproductive advantage. 4.Inclusive fitness is the reproductive fitness of an individual organism plus any effect that the organism has on increasing reproductive fitness in related organisms. 5.Evolution relies on mutations, or small changes in genes.

4. 1.Evolutionary psychologists use evolutionary theory to explain patterns in psychological characteristics. 2.Researchers study mating behavior to investigate aspects of evolutionary psychology. 3.Parental investment refers to all the resources spent to produce and raise offspring. 4.Sexual selection refers to the tendency of females to choose mates passed on certain characteristics, which are then passed on to their male offspring.