Question

Design an experiment that shows that genes affect behaviors

Answer 1

In evolutionary psychology, one pervasive assumption is that how we act is affected by the genes we carry. Does that have good concrete evidence? Are our biological results predetermined? The most intriguing findings have come from twin studies on this issue.

The study of identical twins reared apart is a natural experiment where two individuals with exactly the same genes grow up in different environments. If they turn out to be similar, then the similarity can be attributed to genotype.

One can find similarities between twins when they were reunited for the first time after being separated from birth. Many of the pairs dressed similarly or had the same haircut, or glasses. They described remarkable similarities in hobbies and interests. One pair reported that they were the only ones in their neighborhood to construct a circular bench around a tree in their backyard.

We do have to accept that identical twins are a special case whose significance to ordinary people's actions is questionable. The problem is that several genes affect many different characteristics. If six genes are involved, identical twins would be the same, as they have all six genes.

This wrinkle (known as epistasis) may help explain why it is so difficult to establish a biochemical causation chain between specific genes and complex human behaviors, although researchers have made heroic efforts to account for various traits, such as sensation seeking as a function of dopamine receptors, and researched various candidate genes to account for criminal violence.