Q. Any thoughts for Grandparents Day, which this year is September 12, 2021?
A. Yes. How about this: Archaeological evidence strongly suggests that increasing lifespans, which permitted the creation of an older generation (“grandparents”), played a key role in our evolutionary success. Indeed, this phenomenon may account for why we, as Homo sapiens, replaced archaic humans such as the Neanderthals.
The Fossil Record: Archaeologists have analyzed the fossil records of a handful of sites known to be those of human habitation, yielding fossil evidence to allow them to determine the age of death of our prehistoric ancestors. The best record of age is dental remains. For almost all of our prehistory, going back at least 3 million years, analysis shows that individuals rarely lived beyond the age of 30. However, beginning approximately 30,000 years ago, in a time called the Upper Paleolithic, there was suddenly a fivefold increase in the numbers of individuals living beyond age 30. This has been called the “Age of Grandparents”, and it had far-reaching effects upon our species. Consider the following:
Food Sharing: Grandparents help provide food for young ones, helping to ensure their survival. Even today, there are a few pockets on the globe where hunter gatherer societies still live as they did centuries ago, and we can draw inferences from their current practices . One such group is the foraging Tsimane people in the Bolivian Amazon. Notably, food sharing across generations was found to be key in helping Tsimane individuals survive and flourish: while parents gave the most food to their children, grandparents were the next biggest providers. In essence, the older generation redistributed surplus food down to the younger generation, ensuring their survival success.
Care: Grandparents also provided care to their grandchildren, further increasing their chance of survival. Parents could leave their children in their grandparents’ care while foraging for food. Further, with grandparents assisting in the care of young ones, mothers could then have more children, thereby increasing the size of families, clans and tribes. With increasing numbers came increased survival, as the members of these kinship groups shared their food, protected each other from death due to predation and starvation and developed complex systems of cooperation.
Growing population size also accelerated the pace of evolution as, in these greater numbers, there was more opportunity for advantageous mutations to take hold.
Menopause. It has been suggested that menopause in modern-day human females is consistent with the grandparent theory. Unlike other primates, young human juveniles cannot forage for themselves, but need adult care for many years after birth. If human mothers remained fertile until shortly before they died, their death would likely also result in the death of their late born offspring. In this sense, Menopause is evolution’s secret to success. With fertility ending while mothers are still strong and able to provide care, they can continue to look after their young offspring into adulthood and thereby ensure their survival success.
Cultural and Technical Knowledge. Longevity also allowed for the transmission of cultural and technological knowledge. Examples: where to find food in times of drought and how to make weapons. Longevity also promoted the formation of kinship systems and other social networks which would have made it easier to negotiate the sharing of scarce resources, especially in times of shortages of food and water.
So, here’s to you, grandparents, my own vote for the greatest generation.
Much of the research referenced above is drawn from the excellent article entitled “The Evolution of Grandparents”, by Rachel Caspari, appearing in “Scientific American”, November 1, 2012.