In attempting to explain the delayed starts of menstruation and sexual activity, the researchers ruled out factors such as socioeconomic class. Instead, they conjectured that older brothers may have delayed the physiological maturation of sisters by absorbing more parental resources or by applying psychological stresses. Meanwhile, younger brothers may have delayed girls' behavioral maturation by demanding that their older sisters assume care-taking roles. 　　

为了更好地解释为何女孩初潮以及第一次性关系发生时间会因兄弟的存在而推迟，研究人员排除了某些因素如社会经济等级因素。相反地，他们推测兄长吸取了更多的父亲元素且能够施加心理压力，故而使得女孩子月经初潮推迟。而弟弟希望姐姐承担起照顾自己的责任，从而延迟了女孩们行为的成熟。