needs to be done in this area before a coherent picture of these relationships can be constructed. In the meantime, investigators should be wary of using single and/or "simple" physiological indices as a means of identifying or quantitatively measuring any particular affective state. At the present time, physiological measures of emotion do not really seem to be much "cleaner" or -more scientific" than strictly behavioral measures.
A third lesson to be learned from the nonhuman primate literature on affective development concerns the degree to which such development can be modified, both in the short term and long term, by environmental factors and events. Even though the initial appearance of different types of emotion or affect may be the product of genetically tuned maturation of the nervous system, once a particular pattern of emotional expression has emerged into an individual's affective repertoire, it soon comes under the influence of various environmental contingencies. Previous and concurrent experiences clearly play a major role in shaping an individual's pattern of affective development. Moreover, such environmental factors are not limited in their influence to behavioral expressions of emotion, but include physiological processes as well. It would seem that human affective development should be at least as much subject to influence by environmental factors as is the case for the nonhuman primates studied to date.
Finally, one can look to the recent findings concerning individual differences in affective development among rhesus monkeys for evidence that environmental influences, powerful as they may be, are not necessarily the same for all individuals. Different monkeys often react to the very same environmental events in quite different fashions, and it appears that at least some of this variance can be accounted for by genetic and/or constitutional temperament differences between individuals. Such factors may put some individuals at considerably greater risk for exhibiting abnormal patterns of affective development than others. However, nature and extent of such increased risk will also be influenced by the particular environment in which a given monkey grows up: some rearing environments seem to be far more benign than others for individuals who are at high risk. Such findings emphasize the complexity involved in trying to predict and understand individual patterns of affective development, and they suggest that theoretical models emphasizing genetic environmental interactions or transactions may be far more appropriate for conceptualizing the process of affective development than are more conventional, unidirectional models that emphasize various genetic or environmental factors (cf. Sackett et al., 1981). In view of the monkey data, it is difficult to imagine how these less complicated conceptual models could do justice to phenomena associated with human affective development.
Some of the research described in this chapter was supported by U.S.P.H.S. Grants No. MH-11894 and MH-28485 from the National Institute of Mental Health and by the University of Wisconsin Graduate School. The editorial assistance of Ms. Helen LeRoy is