ness is not linked to the food, becomes adaptive in natural conditions. Along the same lines, Hollis ( 1982) has cogently argued, in an extensive review of the literature, for the adaptive significance of various conditioned BD behaviors.
As a concluding comment, it may be worth noting the complementary nature of the functions proposed for the two categories of CRs. The BD CRs associated with a hedonic shift seem principally oriented toward a modification of the environment through approach and withdrawal behaviors. Rapidly established and not very sensitive to the timing of events, they could have an immediate survival value. The FD CRs seem oriented towards a modification of the organism, in order to cope with a predictable environment, and are apparently more "optional" for survival. Their establishment, generally long in duration, would depend on a finer analysis of the situation and on more strictly defined conditions.
This study was supported by the C.N.R.S. (ERA 79), Université René Descartes, E.P.H.E. (Laboratoire de Psychologie differentielle), and C.N.A.M. (Service de recherches de l'I.N.O.P.). The author would like to thank Drs J. Brener, M. Reuchlin, and two anonymous reviewers for their helpful comments on an earlier version of this paper, and R. Eisenberg for his aid in the final writing.
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