This chapter is concerned with a rather heterogeneous collection of studies on diverse aspects of behavior in many species. For convenience the material has been divided into "simple" and "complex" sections, although this classification does not imply any fundamental difference in the level of organization at which gene action occurs. The common feature of the research reported here is a concern with reflexes, taxes, physiological variation, or deviant motor activity. The investigation of such responses has been predominantly the domain of biologists rather than psychologists. One might expect such responses to have simpler relationships to genes than do general traits like intelligence and temperament. If so, they would have especial importance for behavior genetics. This expectation is sometimes verified, but there is no reason to assume that behavioral and genetic complexity always run in parallel. Perhaps the most important generalization to be drawn from the variety of studies summarized here is the ubiquity of genetic effects. Quantitative measurement of behavior combined with genetic techniques finds an influence of heredity in insects, rats, and men, both in behavior which is relatively unmodifiable in pattern and in behavior which is the outcome of a long period of development under specified conditions.
Circling and Choreic Behavior . A considerable number of "behavior mutants" have been described in mammals and birds. The inheritance of these conditions has always proved to be of the monohybrid type. In those cases which have been thoroughly investigated, lesions of the nervous system have been found associated with the behavioral anomaly. Some of these mutations reduce viability so that the affected class of offspring is numerically deficient or shows impaired life span.