There was a correlation between how well a child grew and survived and their mother’s foraging work. (In modern cultures, how well a mother feeds her children produces the same results.) When another child came along, the grandmother took over the feeding, other motherly duties, and child care so that the mother could focus her energy and resources on having more children. Grandmothers enable the birth of more descendants, leaving more copies of her genes in subsequent generations. Grandmothers are evolutionary heroines!
• Hawkes K (2020). The centrality of ancestral grandmothers in human evolution. Integ Comp Biol. Vol. 60, 765-781. Published 09/2020 http://doi.org/10.1093/icb/icaa029.
• Hawkes K (2020). Cognitive consequences of our grandmothering life history: cultural learning begins in infancy. Phil Trans R Soc. B. Vol. 375. Published 06/2020 http://dx.doi.org/10.1098/rstb.2019.0501.
A PBS article, How Grandmothers Gave Us Longer Lives claims that humans may have developed long life spans because of Nature’s first babysitters: Grandmothers.
A Proceedings of the Royal Society B study,
Increased Longevity Evolves From Grandmothering, used a mathematical model to determine how grandmothers can influence human longevity throughout several generations, giving humans longer life spans than other primates.
Molly Fox, PhD, a PhD student at the University of Cambridge, published studies on the impact of grandmothers on evolution. Dr. Fox added that grandmothers also passed on more than genes to help their grandchildren survive and evolve. “We are a species heavily reliant on the ideas, knowledge, and customs passed on between generations. This may be an important aspect of the advantages a grandmother’s presence affords her family.”
An NPR documentary titled Grandma revealed that mothers and grandmothers kept the children fed more than the hunter father, who only succeeded in 3.4% of his hunting excursions. Grandmothers were crucial to childhood survival in their environment.
Even among different species, a grandmother’s love, wisdom, and prominent roles are displayed beautifully in James Cameron’s TV documentary series, Secrets of the Wales. The skills and displays of mothering are passed on with each new generation, from grandmother to mother to daughter, providing a vitally strong bond for survival.
A 2019 study, Post-reproductive Killer Whale Grandmothers Improve the Survival of Their Grandoffspring, by Stuart Nattrass, Darren P. Croft , Samuel Ellis, +7, and Daniel W. Franks found that grandmothers increase the survival of their grand-offspring in whale populations. Their findings explain why killer whales have evolved the longest post-reproductive life span of all nonhuman animals. The benefits post-reproductive grandmothers provide to their grand-offspring are most important in difficult times when the salmon abundance is low to moderate.
In The Social Behavior of Older Animals, (Johns Hopkins University Press, 2009), Canadian zoologist Anne Innis Dagg states, “Many whale species travel in family pods that include grandmothers and grandcalves. In groups of sperm whales, older females help babysit for the young while their mothers dive for food. Orca grandmothers often lead their pods and can live for decades after they stop reproducing. The oldest known orca, nicknamed "Granny," died in 2016 at over 100. In 2015, scientists writing in the journal Current Biology suggested that these elder orcas help their descendants survive in hard times because they remember all the best places to find food.”
Elephant herds are also famously matriarchal. The grandmother matriarch is highly- respected for her knowledge, guidance, and wisdom. She often leads the elephants out of danger and on their journeys to find water and food. Calves are typically born into groups led by their grandmothers, who can live to around 80 years old.
Mirkka Lahdenperä, a biologist at the University of Turku, Finland, said, “Females in a herd form close bonds and collaborate to raise their young.” She analyzed records from a semi-captive population of Asian elephants working for the timber industry in Myanmar. Some adult females still lived in groups with their mothers, while others were relocated (without their mothers) to different areas. Lahdenperä found that the calves of young mothers were eight times more likely to survive if their grandmothers lived near them than if they were absent. “When calves' mothers were older and more experienced at raising babies, this beneficial ‘grandmother effect’ disappeared even if the actual grandmothers were still around.”
There is anecdotal evidence that they may help nurse their grandcalves, giving them a nutritional boost. But, Lahdenperä thinks the more likely advantage is the wisdom a grandmother elephant has amassed during her long lifetime. For example, if a calf gets stuck in a mud pit, its grandmother might be more successful at helping the calf than its mother. That is because the grandmother has more experience with this situations.
In India, older female Lagur monkeys commingled with their daughters and grandchildren. Zoologist Anne Innis Dagg reported, “The grandmother langurs have a particular job: They aggressively defend the infants against attacks from humans, dogs, and rival monkeys. Some female langurs even give their grandchildren special treatment, grooming them and stepping in when they play too roughly with other young.”