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Introduction
Page 1
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Discussion
Pages 7 - 8 - 9 - 10
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References
Page 11
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By confining the tests to small, relatively empty cages, the present study minimized the complex releasing and directing stimuli by which rats, monkeys, and other mammals orient themselves within complex environments. Also, this means that the present study minimized factors that involve learning and imprinting; it is the sensory analyzers and synthesizers of releasing and directing stimuli that are especially dependent upon experience and developmental factors [Adams, 1979b] .It is also likely that the neural substrate of these analyzers and synthesizers has changed greatly in the evolution of rats and monkeys from their common ancestors. Rats rely largely upon olfactory and vibrissal releasing and directing stimuli; monkeys obviously rely to a great extent upon visual and fingertip tactile stimuli for these functions.
The method of data analysis used here biases the results to fit a particular type of model. By analyzing communications as consisting of a continuous stream of discrete acts and postures, with facial expressions, vocalizations, and pheromone secretion as independent, associated channels of communication, we have "imposed" a certain form upon the results. The assumption is made that this corresponds to the way that the animals themselves are tuned to receive the communication, but the assumption probably needs more rigorous tests than we have been able to give it. It should be noted that, according to this analysis, one cannot conclude that monkeys are more "complex" in their communication than rats. Each have three channels of communication. Whereas monkeys have a channel of facial expression (and to it should probably be added eye contact), rats have their own channel of rapidly changing pheromone secretion which may be far more important than we have been able to determine with our present methods.
In summary, the preceding discussion leads toward the hypothesis that the "outer" parts of motivational systems, their sensory and motor portions, change more rapidly during the course of mammalian evolution than does the inner part, the integrational portion, consisting of the motivational mechanisms. The changes in sensory and motor systems take place as shifts in entire modalities, e.g., mouth to hand or olfaction to vision, that extend across all motivational systems rather than being confined to one or another. Motivational mechanisms do not seem to undergo such gradual transformations; instead, if anything, judging from the example of patrol/marking and display, they may arise or disappear completely, being replaced by new systems. To some extent these hypotheses could be tested by comparative surveys of behavior such as I have done for the muroid rodents [Adams, in press] but extended to more motivational systems and wider ranges of mammals, including primates. Ultimately, however, the question of homology can only be answered with more complete data on the neural circuitry and mechanisms of behavior (see Discussion, and especially the author's response in [Adams, 1979a]).
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