Grandmothers are as much loved for their homemade pie as they are for the love and affection they showered on us as grandchildren. But Science has also proved what grandchildren have known all along. The presence of grandmothers is crucial for the development of the child in its formative years, at times the only constants in their life.
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.
How does the presence of grandmothers contribute to the evolution of a species and increase their lifespan? The single most important factor is care. She can gather food and also feed her grandchildren, a task normally set aside for mothers. The chance of the newborn child’s survival increases as the mother is now able to give it complete attention. She also has more time to forage for good and fulfill her childbearing role. The grandmother takes care of the other children. The result is that both the newborn and the other children are taken care of.
In the hypothetical study, the females who survived past the menopausal stage increased the chances of the grandchildren surviving. So these females had a better chance of their genes surviving and over a period of countless generations, the whole species evolved better and had longer lives.
Hawkins also suggests that the social relations inherent in grandmothering are a significant factor that resulted in a more evolved brain and other distinct traits. Each child is trying to get the attention of its mother as there are more offspring in the fray.
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This creates an atmosphere of interdependence within the family and over time with a larger group. Humans became more social and their brains evolved more.
This theory is not definitive but the mathematical model strengthens the theory to some extent. This provides a basis for anthropologists to study further along these lines.
Maybe it’s time to thank our grandmothers, not only for love, but for our evolution too.
IMAGE FEATURED: Jozef Polc