Menopause
Menopause typically occurs between 49 and 52 years of age. The majority of women have their last period between the ages of 48 and 55. The average age of the last period in the United States is 51 years, in the United Kingdom is 52 years, in Ireland is 50 years and in Australia is 51 years. In India and the Philippines, the median age of natural menopause is considerably earlier, at 44 years. The menopausal transition or perimenopause leading up to menopause usually lasts 7 years (sometimes as long as 14 years).
Menopause
The male-biased philopatry theory proposes that male-biased philopatry in social species leads to increased relatedness to the group in relation to female age, making inclusive fitness benefits older females receive from helping the group greater than what they would receive from continued reproduction, which eventually lead to the evolution of menopause. In a pattern of male-biased dispersal and local mating, the relatedness of the individuals in the group decreases with female age, leading to a decrease in kin selection with female age. This occurs because a female will stay with her father in her natal group throughout life, initially being closely related to the males and females. Females are born and stay in the group, so relatedness to the females stays about the same. However, throughout time, the older male relatives will die and any sons she gives birth to will disperse, so that local relatedness to males, and therefore the whole group, declines. The situation is reversed in species where males are philopatric and either females disperse, or mating is non-local. Under these conditions, a female’s reproductive life begins away from her father and paternal relatives because she was either born into a new group from non-local mating or because she dispersed. In the case of female-biased dispersal, the female is initially equally unrelated with every individual in the group, and with non-local mating, the female is closely related to the females of the group, but not the males since her paternal relatives are in another group. As she gives birth, her sons will stay with her, increasing her relatedness to males in the group overtime and thus her relatedness with the overall group. The common feature that connects these two otherwise different behaviors is male-biased philopatry, which leads to an increase in kin selection with female age.