The long-standing theory of evolution has always been based on natural selection: that traits are favored to promote reproductive success. This makes sense why harmful mutations and diseases appear much later in life, with our bodies more likely to degenerate when we are no longer fertile. This is true across all of the animal kingdoms, for example, in chimpanzees – our closest primate relative – the association between fertility and longevity is very pronounced.
However, humans survive much longer than any other species past this point of infertility, defying the laws of biology as we know them. “From the perspective of natural selection, long post-menopausal life is a puzzle,” said UC Santa Barbara anthropology professor Michael Gurven. “We don’t just gain a few extra years — we have a true post-reproductive life stage.”
Gurven and his team have released a study that challenges the long-standing view of ageist natural selection. Showing that beyond advancements in medicine and healthcare, humans past their reproductive age still have a huge role to play in allowing our species to thrive. Concluding, the secret to our success is actually our grandparents!
The team constructed various models to analyze how grandparents inputted the chance of success of the human species over millions of years. Key factors they found to contribute included food sharing, foraging, increased rate of survival of parents, and teaching the young relevant skills, world views, and how to socialize.
The leading theory in the paper is called the “Grandmother Hypothesis”, which explains how grandmothers help increase the chance of survival of their grandchildren, in turn, enabling their daughters to have more children. “And so that’s not a reproduction, but it’s sort of an indirect reproduction. The ability to pool resources, and not just rely on your own efforts, is a game-changer for highly social animals like humans,” co-author Raziel Davison said.
In summary, the authors found that what sets us apart from other species is the cooperation between all generations. However, this important role is commonly overlooked in our modern society.
“Despite elders being far more numerous today than ever before in the past, there’s still much ageism and underappreciation of older adults,” Gurven said. “When COVID seemed to be most deadly just for older adults, many shrugged their shoulders about the urgency of lockdown or other major precautions.”
They continued: “Much of the huge value of our elders goes untapped. It’s time to think seriously about how to reconnect the generations, and harness some of that elder wisdom and expertise.”
Source study: Proceedings of the National Academy of Sciences – The importance of elders: Extending Hamilton’s force of selection to include intergenerational transfers