1. Various research centers are studying identical twins in order to discover the “heritability” of behavioral characteristics – that is, the degree to which a trait is due to genes (“nature”) instead of environment. They have reached some surprising conclusions. One study found, for example, that optimism and pessimism are both very much influenced by genes, but only optimism is affected by environment, too. According to another study, genes influence our coffee consumption, but not consumption of tea. Anxiety (nervousness and worry) seems to be 40 to 50 percent heritable. Another study tells us that happiness does not depend much on money or love or professional success; instead, it is 80 percent heritable! Among the traits that appear to be largely heritable are shyness, attraction to danger (thrill seeking), choice of career, and religious belief.
2. It is not easy to discover the genes that influence personality. The acid that carries genetic information in every human cell, DNA, contains just four chemicals: adenine, cytosine, guanine, and thymine. But a single gene is “spelled out” by perhaps a million combinations. As the Human Genome Project (which provided a “map” of human genes) was almost complete in the spring of 2000, there were a number of newspaper headlines about specific discoveries: Gene Linked to Anxiety and Thrill Seeking Due to Genetics. The newspaper articles led people to believe that a single gene is responsible for a certain personality trait, in the same way a single gene can be responsible for a physical characteristic or disease. However, one gene alone cannot cause people to become anxious or thrill seeking. Instead, many genes work together, and they direct the combination of chemicals in the body. These chemicals, such as dopamine and serotonin (which affect a person’s mood), have a significant influence on personality.
3. If, indeed, personality traits are, on average, about 50 percent heritable, then environment still plays an important role. Unlike other animals, human beings have choice. If our genes “program” us to be anxious, we can choose a low-stress lifestyle or choose to meditate or do relaxation exercises. But because of the powerful influence of genes, most psychologists believe that there is a limit to what we can choose to do. Thomas Bouchard, a psychologist and the director of one twin study, says that parents should not push children in directions that go against their nature. “The job of a parent,” he says, “is to look for a kid’s natural talents and then provide the best possible environment for them.\
What is the primary focus of research centers studying identical twins?
Identifying the genetic basis of physical traits
Understanding the influence of environment on behavior
Determining the heritability of behavioral characteristics
Investigating the impact of diet on personality