Now, new findings suggest that this amiable shift in lemurs was at least partly driven by changes in the action of the “love hormone” oxytocin inside their brains. In a study published in the journal Biology Letters, Duke University researchers studied seven closely related lemur species in the genus Eulemur, noting which ones had domineering females and which were more egalitarian. Their behavior isn’t the fierce protectiveness of a mother defending her babies, said senior author Christine Drea, a professor of evolutionary anthropology at Duke.