The influence of genes on behavior has been well established in the scientific community. To a large extent, who we are and how we behave is a result of our genetic makeup. While genes do not determine behavior, they play a role in what we do and why we do it.
Behavioral genetics studies heritability of behavioral traits, and it is an overlap of genetics, psychology, and ethology (the scientific study of humans and animals). Developmental genetics, similarly, is the study of how genes influence behaviors. Genetics play a large role in when and how learning, growing, and development occurs. For example, although environment has an effect on the walking behavior of infants and toddlers, children do not usually begin walking before a certain time that is predetermined by genetics. The genetic makeup of a child predetermines an age range for when a child will begin walking, but the influences in the environment determine how early or late the event will actually occur.
Classic or Mendelian genetics, developed by Gregor Mendel (Figure 1), examines how genes are passed from one generation to the next, as well as how the presence or absence of a gene can be determined via sexual reproduction. Gregor Mendel is known as the "father of modern genetics", and his work with plant hybridization (specifically pea plants) demonstrated that certain traits follow particular patterns. This is referred to as the law of Mendelian inheritance.
The ways in which genes can be manipulated can and does have a huge influence on behavioral preferences. Breeding for certain behavioral characteristics can be done through gene manipulation. For example, some dogs are bred specifically to be good hunters. In another example, Seymour Benzer discovered he could breed certain fruit flies with others to create distinct behavioral characteristics and change their circadian rhythms. Genetics have also been successfully manipulated to create a healthy crop of honeybees and decrease the number of diseased bees.
Genetics and the Environment
It is difficult to determine whether genetics ("nature") or the environment ("nurture") have a stronger influence on behavior, and it is largely believed that human behavior is an intricate result of both. For example, a preference for a particular food could be genetically based, it could be because you ate it growing up, or it could be a combination of both. In most cases, behavior is the result of a dynamic interplay between nature and nurture.
Studies on identical twins are often used to determine what can be attributed to genetic influences and what can be attributed to environmental influences. Identical twins share the same genotype, meaning their genetic makeup is the same. Researchers have discovered, however, that the phenotype (or the observable expression of a gene) of identical twins grows apart as they age. Our genes influence how we respond to our environment, and at the same time the expression of our genes are changed by the environment around us; therefore the relationship between genetic and environmental influences cannot be easily separated.