The Genetic and Evolutionary Roots of Behavior
Some of the best ideas in the world have the worstreputations. Take global warming, for example. When scientists in the mid-20th century began to worry that humans’ carbon-spewing, forest-clearing ways were heating up the planet, many people scoffed that the scientists were just tree huggers. Much of the public could not believe that actions as mundane as driving cars and cutting down trees might eventually lead to cataclysmic results. And yet a few decades later, the data are rolling in and the word is getting out: It’s getting hot in here.
Evolution is another good idea that gets a bad rap. For many years, people mocked evolutionists for asserting that humans and apes have a common ancestor. They rejected the notion that the world’s beauty and complexity could be the result of random trial and error—in which the better adapted variations survived, and the less successful ones simply died off. Many people were offended by the idea that nat-ural laws rather than divine direction shaped living organisms.
And yet the data keep rolling in and the word keeps getting out: Evolution and genetics are engines of nature that drive the shapes, sounds, and actions of life everywhere. These truths apply just as surely to humans as they do to orangutans, silverfish, and decorative ferns.
Granted, evolution and genetics have earned some of their infamy. First of all, early versions of evolutionary theory had a few kinks. Because they didn’t know about genes, many evolutionists believed that parents could pass on traits they had gained over the course of a single lifetime to their offspring. According to this theory, say, a giraffe that had to reach for higher and higher leaves would develop a longer and stronger neck, which its calves would then inherit. Even Darwin believed a version of this theory, despite the evidence that it simply was not true.
The study of genetics also suffered from unsavory applications. In the early 20th century, for example, eugenicists and so-called social Darwinists used a corrupted version of evolutionary theory to justify sterilizing, euthanizing, and even murdering people who allegedly carried socially undesirable genes. But in the second half of the 20th century, scientists began to redeem evolutionary theory and genetics research by using them to promote and protect human rights rather than dismantle them. Researchers repeatedly showed that race and ethnicity are to a large extent social constructions, not genetic facts. They demonstrated that genes are only part of the story of development and behavior; the remaining part involves social and environmental conditions—many of which we help to create. And they explained that part of the strength of our species lies in the variability of its members, not in the reproductive suc-cess of a few people with a particular set of traits.
Evolution is one of science’s best established, best confirmed theories, and thou-sands of researchers have built on this framework in powerful ways. These advances have been crucial for psychology—and an understanding of evolution and genetics has become an integral part of the field. We are incorporating genetics into our expla-nations of why some people respond well to antidepressant medication and some do not, and why some individuals are introverted while others are outgoing. An evolu-tionary perspective has provided insights into why people find some types of reason-ing problems difficult and others a breeze, or why men and women tend to react differently to a partner’s sexual infidelity.
As we consider how biological factors shape psychological functioning we’ll start by asking how genes influence us. We’ll need to work through what genes are, how they shape development, and how they eventually influence behavior. Second, we’ll ask how the genes got to be the way they are. This question will lead us to a discus-sion of evolution by natural selection, which is the mechanism responsible for adap-tive genetic changes. Third and most important, we’ll ask how we study the genetic or evolutionary roots of a behavior.