Dominance style, differences between the sexes and individuals: An agent-based model
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In recent studies of primates, the question has been raised whether competitive regimes (egalitarian versus despotic) are species-specific or should rather be considered as sex-specific. To study this problem we use an individual-oriented model called DomWorld in which artificial agents are equipped merely to group and compete. In former studies of this model, dominance style appeared to be strongly influenced by the intensity of aggression: by increasing only this intensity of aggression, a great number of the characteristics of an egalitarian society switched to those of a despotic one. Here, we investigate, using DomWorld, a competitive regime of artificial males and females that differ exclusively in their fighting capacity; males having a higher intensity of aggression and a higher initial capacity of winning, such as may be due to a male-biased sexual dimorphism. Unexpectedly it appears that, in the model, even if the intensity of aggression of males is greater than that of females, their hierarchy is still significantly weaker and thus their society less differentiated and more egalitarian than that of females. The explanation is that, due to the higher initial dominance of males (compare larger body size), single events of victory and defeat lead to less differentiation than among females. The greater the sexual difference in initial dominance between the sexes is the more egalitarian the males behave among themselves compared to the behaviour of the females among themselves. These effects are already visible during the initial phases of the hierarchical development. These results resemble findings among primates; in real primates their degree of sexual dimorphism may influence the competitive regime of each sex.
Affiliations: 1: Theoretical Biology, Biological Centre, University of Groningen, The Netherlands; Department of Information Technology; Anthropo; 2: Center for proper housing of ruminants and pigs, Swiss Veterinary Office, FAT, 8356 Tänikon, Switzerland