Grandmothers? Whats the Evolutionary Use?
In an evolutionary worldview, human grandmothers are a bit of a puzzle. In most animal species, females do not survive long after their childbearing years have ended. Human females, however, can and often do survive for decades after menopause, the hormonal change which concludes their childbearing years at around age 50. Studies such as the one mentioned below apply an evolutionary worldview in an attempt to explain what (or in this case, who) we see around us.
In this worldview, organisms are generally only helpful to the continued survival and evolution of the species if they can reproduce. Once an organism can no longer reproduce, it is merely taking up space and resources that could go towards either the reproducing or young members of the species. So why would evolution favor human grandmothers? Our life span should have evolved to be shorter, especially for women since, unlike men, there is a defined ending to their ability to reproduce. That is the evolutionary problem with grandmothers.
There Must Be an Evolutionary Explanation of Why Grandmothers Exist!
Defying evolutionary beliefs, grandparents have existed throughout recorded human history, and since we must have an evolutionary justification story for everything, the researchers of a new study have woven together an explanation with a slight twist.1 To be fair, this paper is looking specifically at how distance affected the “grandmother hypothesis,” which has been around at least since 2004. And that hypothesis was built upon explaining old age by natural selection in papers going back to at least 1966.2
In a nutshell, the grandmother hypothesis postulates that post-reproductive life spans are selected for in older women because grandmothers gain inclusive fitness benefits by helping their daughters and grandchildren.3 But in this new study, the authors looked at the distance between their mothers and their daughters to determine if there was a correlation. By looking over detailed church records from Quebec, Canada, in an age (16081799) where travel was much more difficult, they discovered slightly overall positive effects of the presence of the (grand)mother living in close proximity when her daughter was giving birth at a younger age and the number of offspring born, as well as lower chances of infant mortality.4 They also found that distance did affect the benefits, with grandmothers who lived over 50 km (31 miles) away providing severely decreased benefit to the mother or grandchildren, suggesting that geographic distance may constrain the ability of the mothers to help their daughters (and grandchildren), resulting in a decrease in fitness benefits with distance.5 But the authors admit that the evolutionary explanation is still elusive.
The question of why prolonged PRLS [post-reproductive life span] has evolved remains unanswered. Evolutionary pathways to prolonged PRLS have yet to be supported. Future research should apply quantitative genetic analyses to test evolutionary genetic hypotheses and assess the relative importance of PRLS hypotheses. The indirect fitness benefits accrued by grandmothers in our study support the proposition that the grandmother hypothesis can, in part, explain PRLS.6
In other words, from an evolutionary perspective, they cannot explain why women live long past their child-bearing years. Although the study mentioned above did find a positive correlation, it was slight and could just as readily be explained as a result of religion and community (French-speaking, Catholic, founder settler population initially). If evolutionary biologists were to be consistent with their evolutionary paradigm, it would seem that the expenditure of community resources on non-reproductive members would outweigh or at least even out the babysitter benefits.
Indeed, when one takes the evolutionary worldview to its logical conclusion, it becomes evident that euthanasia is the natural consequence. Euthanasia, typically defined as the intentional ending of the life of someone who is suffering, is increasingly being broadened to include those who are simply very elderly. In the evolutionary worldview that has increasingly permeated Western culture for over 150 years, this makes sense. Clear out the elderly so resources can be freed up for younger, healthier, and more productive persons.