Scientists have long wondered about the circumstances surrounding menopause. This is a stage unique to humans which we do not even share with our closest relatives, the primates. Is there an evolutionary necessity for women to stop bearing children almost halfway through their lives? On the other hand, the primates bear offsprings till their last days. It’s something that most evolutionary biologists and anthropologists wonder.
A study presented in the Proceedings of the Royal Society B, a journal published by the Royal Society, says that the need for grandmothers can explain this unique evolutionary phenomenon. The grandmother hypothesis or theory, so named by anthropologist and author Kristen Hawkes, from the University of Utah, explains menopause as a part of evolution. It alludes to the role that grandmothers have traditionally played in all human societies.
Grandmothers contribute through their adaptive value when, after menopause, they shift from their child-bearing role to that of rearing their grandchildren, having lost the ability to bear any offspring of their own. By this, they increase the chances of their genes surviving on through their grandchildren.
The contribution from this change in role helped in the development of a whole new spectrum of social capabilities. Over a long evolutionary period, this led to the evolvement of distinct and unique traits like new and more complex skills, bigger brains and the transformation from gatherers and hunters to cultivators. Pair-bonding, the strong affinity between a mating pair also evolved. Along with it, evolved the ability to cooperate and form groups that were mutually beneficial.
Along with Peter Kim, mathematical biologist of the University of Sydney and James Coxworth, an anthropologist from Utah, Hawkins developed a computer simulation that provided mathematical proof for their grandmother theory.
Taking a hypothetical species of a primate, they factored in menopause and the presence of grandmothers as segments of the human social structure. Over a period of 60,000 years, this species of primate evolved differently. They were able to live well over their child-bearing age, surviving till their sixties, and even seventies. Eventually, the population of grandmothers stood at 43% of the total female population.