It has been my impression that behavior geneticists have a gimmick rather than a theory. Some geneticists feel that organisms’ individual differences are largely due to genetic variation and will continue to push this point. This has served to upset the environmentalists. Both seem to be in the same boat as anyone else: Up the creek without an over-all guiding theory.
Data from many species and many types of investigation support the view that hereditary influences upon behavior are not exceptional but are almost universal. The exact nature of the relationship between nature and nurture in the production of individual differences is not settled.
The general issue of the significance of genetic contributions to individual differences may be approached through population genetics and through physiological genetics.
The first method seeks an answer to the question, “How much does genetics contribute?”, the second is oriented to the inquiry, “How does genetics make its contribution?”
The first question has no logical meaning when applied to an individual, for his whole genotype and total life experience contribute to every aspect of his behavior, and their influences cannot be separated. With respect to populations, however, one may ask how much of the observed variation in behavior is attributable to genetic differences and how much to environment.
Knowledge of hereditability is paramount when one attempts to change phenotypes by selection. But, one can also change phenotypes by manipulating the environment, and here it is important to know how genotypes interact with specific environmental factors.
The population aspects of behavior genetics have not been widely studied with quantitative techniques. However, it appears that a great portion of the behavioral variability of both wild and laboratory races is attributable to heredity. Surveys of genetic variation and behavior in populations of small mammals would be very useful in developing general laws for the nature-nurture relationship.
In mammals and, more specifically, in man the adaptive nature of behavior is largely insured through the process of learning. Genetic variation provides a mechanism for adjusting to different environmental conditions including perhaps different social roles. However, the use of biological analogy should not be taken to mean that nonstandard behavior lies predetermined within us, but that the capacity for creative thought may enable an individual to meet the challenge of a new environment by applying culturally learned modes of adaptation in new ways. The modeling effect of society upon the individual and the creative effect of individual deviation from society’s norm both play an important role. Both modes of behavioral adaptation are the product of organic evolution through natural selections.
Natural selection differs in several important ways from artificial selection as usually practiced in laboratory experiments, it would be highly instructive to study the evolution of behavior in the laboratory using natural selection instead of directed selection. Such experiments would test the hypothesis that major changes in the nature of selection will always influence behavior in a relatively permanent fashion by changing the composition of the gene pool.
Our knowledge of human genetics is limited. It cannot determine the outcome of man in his environment based on genes alone. An organism can tolerate a fair amount of deviation from biological ideals or norms. The more variety it can tolerate, the broader the niche it will be able to occupy. So too a culture with a ready supply of diverse adaptive models will be able to adjust to changing conditions.