Trying to define behavioral genetics can be difficult. In simple terms, it is the study of genetics in relation to the outward behavior of an organism that is seen. So in other words, it is the study of the hereditary factors of behavior. Included in these studies is the study of human genetics, because behavioral genetics studies both the genetic side of behavior and the environmental effects of that behavior. Behavior, like all other inherited traits is very complex, involving multiple genes making it very difficult to pinpoint behavior to any one particular genetic contribution.
Many studies have been done to determine the biological basis for behavior. An increasing number of studies have been done on animals, studies that are looking for the human genetic disorders. These disorders are thought to have a behavioral component. Animal models can be used to study particular diseases in hopes of finding a strong correlation between genetics of disease and the effect of the environment.
Most behavioral studies in humans have involved twins, triplets and adoptees to see how much of their behavior is determined genetically and how much it is influenced by their environment. Through studies of identical twins, researchers have found that those identical twins reared or living apart do not behave exactly the same way giving more value to the influence of one's environment.
In addition to these studies, scientists have been studying the genetic connection to such diseases as schizophrenia and bipolar disorder while they search for the genes they think may give rise to these conditions. Every once in a while studies try to find a correlation between genetics and homosexuality, intelligence and criminal behavior.
Even though heredity plays a part in human behavior other circumstances certainly play a role. For example, a person may have a genetic predisposition to become an alcoholic, but may never drink. Another example is the person who is genetically predisposed to emphysema, but who never smokes.
The effect of a single gene related to mental retardation has been studied in relation to behavior. Research has shown that there are many metabolic pathway defects related to mental retardation that can be traced to a single gene. Some people with retardation have metabolic disorders which may be related to just one gene. Some people with this type of disorder show extreme anger and outbursts which tends to strengthen the link between genetics and behavior.
On the other hand, as long as an organism's environment is reasonably stable, the environment tends to play a somewhat equal role in the organisms behavior. Psychologists tend to believe that an organism's behavior is based on both its genetic makeup and its environment, but proving this is as difficult as finding some of the genes responsible for genetic aberrations. It is very important for the study of families and populations for a large enough sample to be considered. Without the large sample or population, any conclusions that may be drawn, may not be accurate.
More studies need to be done to validity results done up until this point, but no matter what is found it doesn't seem like genetics or environment will win out. The best that we can do for now is continue to look for more information regarding the link between behavior, genetic and the environment, because there is no easy solution.