by Ilona Nenko
From an early age, many of us learn that our grandmothers are invaluable in our lives. Their experiences, help, and knowledge can shape us into who we are today, and their influence stretches far beyond simple stereotypes. Grandmothers have long held a special place in almost every culture, and the human story without grandmothers is not much of a story at all. If we look back in time we find that they were even more valuable than they are in the present, with strong empirical evidence that they have helped grandchildren to survive and aided the fertility of their own offspring. These benefits to relatives are thought to have played a role in the evolution of the extended post-reproductive lifespan that separates us from other great apes. In case it isn’t clear by this point, we think grandmothers are very important. But, is every grandmother equally important?
Well, as it turns out, no. Context-dependence is crucial in the expression and outcomes of helping behaviours in other cooperative species, and humans are no different. We have a lot of evidence that maternal grandmothers play a special role in the lives of grandchildren, moreso than paternal grandmothers. It begs the question then, are all grandmother-related grandchild outcomes the same? This is an interesting question because not all grandchildren are born equal. The circumstances of birth can be hugely influential in early life: firstborn children have different outcomes to later births, twins differ in outcomes than singletons, siblings born in a short time frame can suffer negatively compared to those with a longer interval between births, and children born out of wedlock often have worse outcomes than those born within unions. These statuses may seem to be very different at a surface level, but all have a lot in common: higher risk of low birth weight, higher risk of getting lower Apgar scores, higher risk of being born prematurely and – consequently – lower chance of survival. Bad starts are just that – bad – but don’t necessarily spell doom. History is littered with examples of poor starts being overcome. Sometimes all it takes to turn around a tough beginning is a bit of luck. Sometimes it takes a little helping hand.
Here is where grandma returns. Given there are so many bad starts children could face, and given grandmothers are known to provide benefits (at least some of the time), we decided to investigate whether grandmothers increased the chances of survival of children who experienced hard starts to life. We studied Finnish genealogical data from 1730-1895, a time when medical care was very basic and contraception was not available; childhood survival was low, adult life expectancy was much lower than today, and birth rates were high. Grandmothers were very much needed. Finland is an exceptional country for doing this kind of study – Lutheran priests kept extensive records on the population, giving us a rare opportunity to look at ordinary lives in the past, and we know much of how the society operated. We also know from other work with this Finnish population that grandmother presence was not always helpful, particularly if the grandmother was frail. But did grandma help when the going got rough?
The lack of beneficial survival outcomes of grandmother presence for these poor starts reinforces the importance of investigating different contexts of possible help, and perhaps adds another piece to the slowly unraveling mystery of the evolution of extended post-reproductive life.
Alas, in most of the investigated bad starts, grandmother presence was not beneficial. Firstborns, twins, babies born two years after their older siblings, nor illegitimate children –had an increased chance of reaching the age of five if their grandmothers were alive or not. The lack of beneficial survival outcomes of grandmother presence for these poor starts reinforces the importance of investigating different contexts of possible help, and perhaps adds another piece to the slowly unraveling mystery of the evolution of extended post-reproductive life.
It wasn’t all bad news for these historic Finns though: grandmothers were extremely important to children who welcomed a younger sibling before their second birthday, with a massive 41% increase in the probability of surviving to age 5 compared to grandchildren with no grandmother. It isn’t too difficult to see why: the mother had to focus on the fully-dependent, far needier younger child, and it would therefore benefit her and the child if others in the family – chiefly the grandmother – could help. Grandma benefited from this too – by increasing the chances of survival of her daughter’s children, she increases not only the reproductive success of her daughter, but also her own biological fitness. In a way, by caring for her daughter and her grandchildren, she also cares for herself.