Grandmothers and Evolution: How they have shaped each other over time.
Updated: Apr 30
"Every house needs a grandmother in it." - Louisa May Alcott
As one of the most influential and loved figures in a family, grandmothers hold a special place in the hearts of many people. Whether it is their nurturing nature, wisdom, and life experiences, grandmothers undoubtedly play a critical role in family dynamics. In honor of grandmothers, let’s take a closer look at their impact and importance.
The presence of grandmothers goes far beyond sentimental implications as they may be responsible for the success of the human species. Evolutionary biologists have long been struck by two unique features of humans. First, we enjoy some of the longest life spans in the animal kingdom. In just the past 200 years, there has been an unprecedented increase in how long we live, not just in the richest countries, but also in the poorest. We have moved so far away from our hunter-gatherer ancestors that their life spans are more similar to those of apes and chimpanzees than to modern human beings.
This feature is coupled with another. To a biologist, an organism that cannot reproduce is of little value and an oddity in evolutionary terms. Scientists have been puzzled by the long postmenopausal life of human females. From a purely evolutionary perspective, grandmothers could be considered a failure of reproductive fitness – After all - what good is an organism that cannot reproduce and cannot help perpetuate the species?
The Orca Matriarch can live up to 100 years and is responsible for teaching multiple generations of her family group communication skills, how to find food, and to avoid predators.
As newly published studies confirm, grandmothers may not only help perpetuate humans but are also one of the reasons why we have such long lives. Humans are not the only mammals with a long post-reproductive phase of life. Scientists have identified other mammals such as orca whales (up to 90 years), humpback whales (up to 100), bowhead whales (up to 200 years) and both African and Asian elephants (up to 70 years) with long post-reproductive life spans. These species also have a matriline-led social structure, meaning the most senior female is the leader. Matrilineal knowledge is critical to physical and cultural survival. The older females are a bank of knowledge for their family, such as knowing where the food is, migration routes, passing on languages, acceptable social behavior, and how to avoid predators.
It turns out that these two features – long life spans and long post-reproductive lives, might be connected through “the grandmother effect.” By helping raise their grandchildren, the grandmothers of humans, whales, and elephant family groups allowed their daughters to have more babies.
Grandmothers relieve mothers of some of the child-raising responsibilities, resulting in the ability of the mothers to have more children while also making it possible for those children to have longer lives by helping them during the dependent and fragile early years of life. This implies that grandmothers benefit from what’s called “inclusive fitness”, an evolutionary term that refers to the ability of an individual to pass on its gene pool to the next generation.
There are two studies, both published in Current Biology, that strengthen this theory. An analysis of church birth and death records in Finland for individuals born between 1731 and 1890 illustrated the correlation with having a maternal grandmother between 50 and 75 years of age, while a grandchild was 5 years old or younger increased the probability of the child’s survival. The effect disappeared for grandmothers older than 75 years of age, possibly because they were no longer able to assist with child-rearing. The effect on longevity was seen mostly with maternal grandmothers and not paternal grandmothers.
A second study digs deeper into this effect, revealing that it is not just the existence of a grandmother, but her proximity that is important. The shorter the distance between grandmother and grandchild, the more involved the grandmother can be and the more benefits that benefit her daughter and grandchildren. Both of these studies strengthen the pre-existing case for grandmothers and the indications of just how important they have been to the success of not only our species but others as well.
For centuries, grandmothers have provided assistance that enables families to grow and prosper. Yet more families live by themselves, without grandparents, than at any time in the past. Globalization is transforming family dynamics as a result of emigration and immigration and other changes in societies. For example – At the start of the 20th century only 7 percent of post-reproductive women lived alone. That peaked at 38% in the 1990s and now is at about 32%. If this dispersion continues - Could we possibly reverse the evolutionary role that grandmothers have contributed to human longevity?
"Grandfathers are just antique little boys." - Unknown
A better understanding of the role that grandmothers do and could play as well as facilitating multigenerational family units could not only help mothers but also grandmothers. Grandmothers would benefit from help from their children as they need care as they age. We can’t forget about the grandfathers as they need to be part of the equation. As fathers have taken on an increasing role in parenting, so should grandfathers. Research indicates that children who grow up in multigenerational homes have better high school graduation and college enrollment rates and fewer emotional and behavioral problems than those who don’t.
Although we now credit medical science for lifespans increasing, grandparent involvement remains the norm in many modern societies. Think of it as a reminder that they may have been the ones to give us the initial evolutionary boost in the first place.