Goals of Behavioral Genetics - Personality Psychology

They understand the primary goals of the field of behavioral genetics, let’s look at a concrete example – individual differences in height. Some individuals are tall, such as basketball player Shaquille O’Neal (over 7 feet). Other individuals are short, such as actor Danny de Vito (around 5 feet). Geneticists focus on the key question “What causes some individuals to be tall and others to be short?” In other words, what are the causes of individual differences in height?

In principle, there can be a variety of causes of individual height differences. Differences in the diet while growing up, for example, can cause differences in height among people, genetic differences can also account for some of the differences in height. One of the central goals of genetic research is to determine the percentage of an individual difference that can be attributed to genetic differences and the percentage that is due to environmental differences.

In the causes of height, both environmental and genetic factors are important. Clearly, children tend to resemble their parents in height – generally, tall parents have taller than average children and short parents have shorter than average children. And genetic research has confirmed that roughly 90 percent of individual differences in height are indeed due to genetic differences in height, which is far from trivial. In the United States, average adult height has increased in the entire population by roughly 2 inches over the past century, most likely due to increases in the nutritional value of food eaten by U.S. citizens. This example brings home an important lesson: even though some observed differences between people can be due to genetic differences, this does not mean that the environment plays no role in modifying the extent of such differences.

The methods used by behavioral geneticists, which we will examine in this chapter, can be applied to any individual difference variable, they can be used to identify the causes of individuals differences in height and weight, differences in intelligence, differences in personality traits, and even differences in attitudes, such as liberalism or conservatism, and preferences for particular styles of art. The methods have been applied to all of these phenomena.

However, behavioral geneticists are typically not content with determining the variance percentage due to genetic and environmental causes. Percentage of variance refers to the fact that individuals vary, or are different from each other, and this variability can be partitioned into percentages due to different causes. Behavioral geneticists also are interested in determining the ways in which genes and the environment interact and correlate with each other. And they are interested in figuring out precisely where in the environment the effects are taking place – in parental socialization practices, for example, or in the teachers to which children are exposed. We will turn to these more complex issues toward the end of this chapter. But, first, we must examine the fundamentals of behavioral genetics: what is heritability, and what methods do geneticists use to get their answers?