The development of grooming and its expression in adult animals.

We have seen that grooming is a class of heterogeneous activities, widely represented in animal taxa, yet sufficiently homogeneous within some phyletic groups to generate and test phylogenetic hypotheses. In the life of the grooming animal, the functions served by these activities are also diverse. Similar acts of grooming may serve different functions in different species or in different contexts. Sometimes these different functions can be discovered by careful attention to variations in the spatiotemporal patterning or sequencing of grooming elements. In several species a general cephalocaudal progression has been noted during both the ontogeny of grooming and during its expression in adults. During early development and in adulthood, the components or functional units of grooming appear to be hierarchically organized. Scratching with the hindpaw, for example, appears in rodents to be separate from the hierarchical branches in which one finds licking and face wiping. At least some transitions between functional units can be predicted from changes in the temporal patterning of one grooming unit (e.g., eye wipe) just prior to the onset of another unit (e.g., ear wipe). Analyses of genital and other types of grooming during two forms of sexual activity (copulation and the display of penile erections ex copula) were used to demonstrate once again that the stimulus regulation of grooming is context dependent. Among the implications of this review for the physiological study of grooming are the following: 1. Careful attention should be given to the spatiotemporal patterning of grooming, in order to reduce errors of "lumping" and "splitting" in classifying grooming acts, and also to detect alterations in the patterning when they occur. Such changes in patterning may be assumed to reflect changes in the physiological state of the animal. 2. Grooming acts that appear formally similar in different contexts may operate under rather different physiological systems. 3. Experimental manipulations may affect grooming directly, that is, by generating grooming efference without changing afference, or indirectly, by altering the "motivational state" or by creating stimulation that potentiates grooming, as from itching or from reafference due to provoking other behavior patterns.