The promiscuous systems of the monotremes, didelphids, dasyurids, and insectivores, as well as the spatial monogamy of tree shrews and elephant shrews are very similar to the dispersed multimale/multifemale system and the dispersed monogamy found in cheirogaleids and lorisiforms. The spatial aspects of social organization are in fact the same in promiscuous and dispersed polygynandrous systems on the one hand and in spatial and dispersed monogamy on the other hand. The difference is that in each case social networks are present in the latter (i.e., in cheirogaleids and lorisiforms), but not in the former system (i.e., in all other groups). As a result, Müller and Thalmann (2000) have suggested that the most likely scenario regarding the origin of primate social organization is that a dispersed multimale/multife-male pattern arose from promiscuity. Such a dispersed multimale/multifemale pattern is found in all the species of mouse lemur (Microcebus sp.), which have so far been investigated, in Mirza coquereli, as well as in the majority of species of bushbaby and in the slender loris.
Many of the species that are organized in dispersed multimale/multifemale groups are characterized by the presence of matriarchies. This is the case in most bushbabies, as well as in mouse lemurs (Bearder, 1987; CharlesDominique, 1977; Kappeler et al., 2002; Radespiel et al., 2001; Wimmer et al., 2002). This relatedness between the females of multimale/multifemale groups might have been at the origin of the development of social networks as the evolution of sociality is believed to have involved kin selection (WestEberhard, 1975). We, therefore, argue that the ancestral pattern of primate social organization was a dispersed multimale/multifemale system with the core group being formed by related females, which engaged in social contacts with some males. Thus, in the earliest primates, groups of related females were at the origin of the evolution of social networks from the ancestral system of promiscuity.
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