Why the love of a grandmother can be more self-serving than it seems
My grandmother loves me. I hope yours does too (I really do). Apparently, this is how it is supposed to be. We don’t get urges to kill our families. Quite the opposite; we cooperate and stick together. The older generations take care of the younger ones and guide them through life with wisdom and platonic care for their children. But why exactly do grandmas love their grandchildren? Possibly because kids are cute, they have a babbling mouth that needs wiping every three minutes, and abandonment is a taboo in the majority of societies. There are more than a hundred cultural reasons why you love your family and why grandmas take care of children.
What interests me, though, is how we can biologically explain the love of a grandmother. You might ask, “What is so special about a grandmother’s love?” and I’ll tell you that it is a much more sentimental love than that of a mother. Emory University research shows that pictures of children elicit an activation of the part of a grandmother’s brain that is related to emotional empathy, while pictures of adult children are associated with cognitive empathy. As such, grandmas feel a more intense, irrational love for children that is disassociated from logic. Now, why is that? The short answer is menopause—although it is complicated.
But before we get there, it is worth discussing why we care about our family as a whole: genes. The biological purpose of any human is to reproduce and pass down their genes; it is advantageous to show care for those that carry a part of you. Furthermore, the death of a relative is considered a biological tragedy. Unless they leave behind offspring, the time and resources spent raising and educating them have been lost. A certain type of monkey, the gelada, will spontaneously miscarry their pregnancy if a new dominant male takes over, as the offspring will be killed to avoid competition. The mother will save more resources by aborting early, rather than investing them in a doomed litter. But how, you might ask, does this relate to grandmothers? I just like geladas. But it’s also a memorable example of how strategic and conditional reproduction often is. Grandmothers are not too different; they want to make sure that (A) their resources are spent in a smart way and (B) that relatives achieve reproductive success and pass on their genes.
According to the grandmother hypothesis proposed by George Christopher Williams, it all has to do with menopause. Have you ever asked yourself why women live past their reproductive age? Williams argued that menopause is an adaptation that limits the reproductive potential of older women to redirect resources into the education and growth of her dependents. It also prevents the risks associated with pregnancy and birth at old age. The hypothesis is further supported by the studies of Kristen Hawkes, an anthropologist researching the Hadza tribe in Tanzania. She observed how the presence of a grandmother in a community increased the reproductive success of later generations and child survival rates. The grandmother, free from her reproductive role, foraged for food and educated the youth, allowing mothers to have more children.
Although menopause appears to be an unusual adaptation, the mechanism behind it is no less exciting. Menopause favours kin selection, a phenomenon in which a trait is favored due to its positive effect on the reproduction of relatives. As shown by Hawkes, menopause was selected to increase the reproductive success of the mothers. But what do the grandmas gain? Their genes are passed at a higher rate than if menopause did not occur. This is known as Hamilton’s rule, which states that altruistic behaviour happens when the relatedness between two individuals, multiplied by the number of offspring that relative gains from your help, outweighs the number of offspring you would produce yourself. This is exactly why it has been rumoured that JBS Haldane, the guy behind the primordial soup theory, famously joked that he would willingly die for two brothers and eight cousins!
Of course, many questions arise from this hypothesis, such as why males retain their reproductive functions into old age, or how did menopause evolve in the first place? But it’s interesting to look at your grandma and think that behind that wrinkled face there is only one wish: the desire for you to stop writing articles and get out and get a girlfriend. Sorry, Grandma, I still have the conclusion left. The grandmother theory is just the first step in trying to understand how evolution subtly affects our behavior. It is just a small part of the larger evolutionary debate about free will and whatnot, but we need to keep asking questions. No matter how childish they may be, and regardless of the answers…I love you, Grandma!