References 55evolutionary problems the animal must solve, we protect our-
selves from explanations that assume an unlimited number of
“motivations,” as did the old theories of instinct. In addition,
this focus on the functional aspects of motivational processes
forces us to consider both the ecological niche that the animal
occupies and the organization of the behaviors it uses to cope
with the problems of the niche.
This explicitly ecological view allows the concept of mo-
tivation to make contact with behavioral ecology and evolu-
tion. Learning and genetics are not the sole determinants of
behavior; an animal’s ecological niche must also be consid-
ered. Animals have evolved solutions to specific environ-
mental problems, and an understanding of these relationships
can inform psychological theories of motivation and learn-
ing. Collier and Johnson (1990) suggested that appreciating
that small predators are themselves potential prey gives in-
sight into the differences in feeding rate between small and
large predators. Indeed, Fanselow et al. (1988) have demon-
strated that predatory risk is an important determinant in the
initiation of feeding behavior. Traditional homeostatic per-
spectives could not contribute this insight.
In addition to highlighting the importance of ecological
variables in determining motivational influences on behavior,
the analyses presented in this chapter can also be used to
examine similarities and differences between motivational
systems. A persistent theoretical problem in theories of moti-
vation has been specifying the number and form of motiva-
tional processes with which an animal is equipped. We have
suggested that the animal is equipped with as many motiva-
tional systems as there are classes of problems in the environ-
ment for it to solve. We expect that the reader has been struck
by the amount of similarity between the response organiza-
tions proposed to account for feeding and sexual behavior, and
to a lesser extent between those structures and that proposed to
account for the organization of defensive behavior. Each con-
sists of a collection of motivational modes organized by some
kind of imminence continuum. Each includes a set of preexist-
ing stimulus processing and response production tendencies.
The extent to which these similarities are valid remains to be
determined, and this question deserves study. Just as interest-
ing are those disparities between the response organizations.
Appetitive behavior in the feeding behavior system is ex-
tremely flexible. Flexibility in sexually motivated appetitive
behavior has also been demonstrated but is much less well in-
vestigated. In contrast, defensive behavior seems more rigid,
perhaps due to the inherently conservative nature of defense.
The behavioral systems view suggests that motivation is
a much more complex phenomenon than that described by
theories of drive, incentive motivation, or opposing affective
states. Any complete conception must include physiological,
psychological, ecological, and evolutionary factors. Our
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