The role of genes may seem obvious when we are discussing physiologic disease, but less so when considering social and behavioral phenotypes. Social and behavioral scientists will need no convincing that biology isn't the whole story, and geneticists are learning more about the importance of environment. However, there is ample evidence of a biological contribution to behavior, which lays a foundation for understanding how genes and environment may interact.
Behavior often is species specific.
A chickadee, for example, carries one sunflower seed at a time from a feeder to a nearby branch, secures the seed to the branch between its feet, pecks it open, eats the contents, and repeats the process. Finches, in contrast, stay at the feeder for long periods, opening large numbers of seeds with their thick beaks. Some behaviors are so characteristic that biologists use them to help differentiate between closely related species.
Behaviors often breed true.
We can reproduce behaviors in successive generations of organisms. Consider the instinctive retrieval behavior of a yellow Labrador or the herding posture of a border collie.
Behaviors change in response to alterations in biological structures or processes.
For example, a brain injury can turn a polite, mild-mannered person into a foul-mouthed, aggressive boor, and we routinely modify the behavioral manifestations of mental illnesses with drugs that alter brain chemistry. Geneticists also have created or extinguished specific mouse behaviors-ranging from nurturing of pups to continuous circling in a strain called "twirler"- by inserting or disabling specific genes.
In humans, some behaviors run in families.
For example, there is a clear familial aggregation of mental illness, substance misuse, and personality traits
Behavior has an evolutionary history that persists across related species.
Chimpanzees are our closest relatives, separated from us by a mere 2 percent difference in DNA sequence. We and they share behaviors that are characteristic of highly social primates, including nurturing, cooperation, altruism, and even some facial expressions. Adaptive behaviors can be conserved through natural selection and evolution in the same way as physical features.
- Connection between phenotype and genotype in our Variation module
- A consideration of the biological pathways underlying behaviors is explored further in the Research in Action example Exploring Genetic Methods, which discusses nicotine abuse.
- Determining underlying genetic contributions to complex behaviors in our Research in Action example Linking Genes with Environment, which focuses on major depression.