||IV. Male Animals Are Not Consistently More Aggressive Than Females||Page 6|
In many other mammals there appears to be a similar brain mechanism that enhances intermale fighting. It may be associated with male territoriality in some species and with intermale displays and fighting in the presence of females during the breeding season in other species. This fighting can be quite spectacular in species with sexual dimorphism in which the males have developed special tusks or antlers which are used in the fighting. It is this phenomenon, well publicized by mass media, which makes many people think that animal aggression is primarily by males.
There are many mammalian species which contradict the popular image because females are as territorial (and in some cases more so) as males against unfamiliar members of their species. I have reviewed this among muroid rodents and found that it is the case in the following genera and species: Rattus rattus; Mesocricetus; Sigmodon; Notomys alexis; Otomys; and Microtus. Also, under wild conditions, laboratory species such as rats and mice are more aggressive in general against unfamiliar intruders, and females in particular are more aggressive than in the laboratory. As a result, laboratory studies systematically underestimate female aggression. I have suggested that the decreased offense of laboratory animals may be due to a tendency for colony odors of laboratory animals to be more homogeneous, thus reducing the activation of the sensory analyzer for unfamiliar pheromones in the laboratory (Adams, 1980).
Pregnant and lactating females are especially aggressive in most mammalian species-a type of aggression which is obviously missing from males. In the laboratory rat, this maternal aggression is apparently due to activation of the offense-motivational system, according to recent data in our laboratory being prepared for publication.
There is no reason to think that the intermale aggression cited above is any more "important" or pervasive in mammals than is maternal aggression. In fact, one of the classic studies of wild rats found the most important determinant of a male's territoriality was the extent to which the male's mother had shown maternal aggression and protected her territory against the intrusion of other rats (Calhoun, 1962). A similar situation seems to hold in primates where the phenomenon has been studied; among Japanese macaques, dominant males are the sons of dominant females (Eaton, 1976).
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