Female social dominance over males is unusual in mammals, yet characterizes most Malagasy lemurs, which represent almost 30% of all primates. Despite its prevalence in this suborder, both the evolutionary trajectory and proximate mechanism of female dominance remain unclear. Potentially associated with female dominance is a suite of behavioral, physiological and morphological traits in females that implicates ;;masculinization’ via androgen exposure; however, relative to conspecific males, female lemurs curiously show little evidence of raised androgen concentrations. In order to illuminate the proximate mechanisms underlying female dominance in lemurs, I observed mixed‐sex pairs of related Eulemur species, and identified two key study groups ‐‐ one comprised of species expressing female dominance and, the other comprised of species (from a recently evolved clade) showing equal status between the sexes (hereafter ;;egalitarian’). Comparing females from these two groups, to test the hypothesis that female dominance is an expression of an overall masculinization of the female, I 1) characterize the expression of female dominance, aggression, affiliation, and olfactory communication in Eulemur; 2) provide novel information about the hormonal and neuroendocrine correlates associated with the expression of female dominance; 3) investigate the activational role of the sex-steroid hormones in adult female Eulemur using seasonal correlates of hormonal and behavioral change; and 4) examine the specific role of estrogen in the regulation and expression of sex-reversed female behavior in these species. In doing so I highlight significant behavioral and physiological differences between female-dominant and egalitarian Eulemur and show that female dominance is associated with a more masculine behavioral and hormonal profile. I also suggest that these behavioral and hormonal differences may be the result of fundamental differences in the biosynthetic pathway associated with estrogen production. Moreover, I assert that these putative physiological differences could provide a parsimonious proximate mechanism explaining the evolution of female dominance and its subsequent relaxation in egalitarian Eulemur species.
