LB021-022

LB21-22
IV. GENETIC FOUNDATIONS OF BEHAVIOR
We have constructed a picture of behavior consisting of a fixed matrix (that is, species-specificities delimited by characteristic anatomical and physiological processes), which an individual can never learn to transcend, coupled with varying degrees of freedom for combining existing, built-in skills and traits. If thess skills and traits are, indeed, programmed into the individual as is implied here, then we ought to be able to adduce evidence for inheritance of such traits. Moreover, the history of evolution should give us some clues regarding phylogenetic emergence of behavior. Such evidence and clues do exist.

Genetics of behavior were first summarized by Hall (1951) and more recently treated in greater detail by Fuller and Thompson (1960). Genetic influences upon various aspects of behavior have been demonstrated for many species. Several studies were made on the fruitfly. Erlenmeyer-Kimling et al. (1962) bred Drosophila melanogaster selectively to produce strains with vastly different geotactic responses (going against or toward the pull of gravity in an appropriate maze). Selective breeding experiments on rats were reported by Rundquist (1933), varying the amount of spontaneous activities in the strains developed; by Tryon (1940), producing maze-bright and maze-dull strains, and by Hall (1951), varying emotionality (as measured by frequency of urination and defecation). It is true that in these experiments it is often not clear exactly what is transmitted genetically. Searle (1949), for instance, poined out that the behavioral difference demonstrated by Tryon may be a result of a factor of congenital timidity, the dull rats actually being upset about the experimental arrangement, whereas the bright ones are undaunted by the maze. Searle’s interpretation may very well be correct, but it does not alter the basic fact that genes do make a difference in the execution of behavior (Fuller and Thompson, 1960). In some instances, the breeds resulting from artificial selection of mates may behave differently from each other because of morphological differentiations (James, 1941). In other instances, morphological changes that are usually inevitable in breeding experiments may be irrelevant to the behavioral changes observed. In this case, physiological processes are altered, thus raising or lowering thresholds of responsiveness.

This was most directly demonstrated by Herter (1936) who showed different thermotactic optima in gray and white mice (where the color of the coat is apparently irrelevant) and by Setterfield et al. (1396), who shoew that the inablility totaste phenylthiocarbamide is inherited in man as a recessive Mendelian trait. Scott and Charles (1954) make a similar point, extending it generally to the interaction between the genetically given and the environmentally modified. In summarizing their work on dogs, they state: ”…different thresholds of response to minimal…stimulation tend to produce all-or-none responses, and the process of habit formation tends to cause individuals to react one way or the other, producing increasingly clear-cut differences.

This point is very well taken. It seems unlikely that genes actually transmit behavior as we observe it in the living animal because the course that an individual takes in its peregrinations through life must necessarily depend on environmental contingencies which could not have been “programmed and prepared for” in advance. Inheritance must confine itself to propensities, to dormant potentialities that await actualization by extra-organic stimuli, but it is possible that innate facilitatory or inhibitory factors are genetically transmitted which heighten the likelihood of one course of events over another. When put into these terms, it becomes quite clear that nature-nuture cannot be a dichotomy of factors but only and interaction of factors. To think of these terms as incompatible opposites only obscures the interesting aspects of the origin of behavior.