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.

Read the paper: Will granny save me? Birth status, survival, and the role of grandmothers in historical Finland

by Richard Johnson, William Wilson, Sondra Bland & Miguel Lanaspa

How does sugar effect our behavior in modern environments? Here we present the hypothesis that fructose, which is present in added sugars such as table sugar (sucrose) and high fructose corn syrup (HFCS), may have a role in behavioral disorders associated with impulsivity and anxiety. This hypothesis is based on recent research that has found fructose to be distinct from other nutrients in activating a survival pathway that includes foraging for food as one of the behavioral responses. Specifically, fructose is distinct from other foods in that it during its metabolism it can lead to a reduction in intracellular ATP levels. This leads to the degradation of AMP that eventually generates uric acid. The accumulation of uric acid and fall in ATP are associated with a variety of metabolic responses that include the stimulation of hunger and thirst, foraging, the development of insulin resistance, and the production and storage of fat. While this is used by animals in the wild as a survival mechanism to help them store fat in preparation for times when food is unavailable, we posit that the overconsumption of added sugars today is leading to chronic stimulation of these pathways. Foraging, in particular, is associated with risk taking (entering unknown areas), impulsivity and rapid decision making, and even aggression. Here we review the evidence that chronic stimulation of foraging behaviors from consuming fructose might carry increased risk for disorders associated with impulsivity and anxiety, including ADHD and bipolar disorder. We recommend further research to investigate the possibility that fructose ingestion might be a contributory risk factor for these and related disorders.

Watch the video summary of our work, below (shared with permission)

Read the paper: Fructose and uric acid as drivers of a hyperactive foraging response: A clue to behavioral disorders associated with impulsivity or mania?

by David W Lawson

Feature image : A household interview, Mwanza, Tanzania; Credit: David W. Lawson

Over the last decade, my colleagues and I have grappled with the categorization of multiple forms of marriage as definitively costly to women by international development and global health organizations. Chief among these practices are polygynous marriage (sharing a husband with a cowife), ‘child marriage’ (marriage under 18 years), and most recently in our new paper in evolution and human behavior, marriages in which the husband is substantially older than the wife. Each of these phenomena are especially relevant across sub-Saharan Africa where, for example, 40% of girls marry before their 18^th birthday.

As an applied anthropologist, I’m immediately wary of ethnocentrism when any practice common in the Global South is categorized as inherently harmful. A widespread tendency to frame these issues through a moralizing lens also raises concern. Plan International’s award winning ‘#stopthewedding’ campaign, for example, presents child marriage as both ‘grotesque’ and demanding of urgent external intervention. Narratives that (over)emphasize the dangers of ‘traditional culture’ can be problematic if they reinforce damaging stereotypes and sideline recognition of broader structural drivers of gender inequality. Anthropologists (and historians) have responded by illustrating the ways in which practices like early marriage may be viewed, not as the product of a morally bankrupt society, but rather rational responses to specific socioeconomic and sociopolitical circumstances.

In this sense, I am also optimistic about the potential contributions of an evolutionary perspective. The polygyny threshold model, for example, suggests that sharing a husband may be beneficial if a man is wealthy enough to provide for multiple wives. A model that receives support in some settings, but not others. And while early marriage has clear potential to be costly (e.g. via elevated risk of early pregnancy), life history theory reminds us that such costs may be tolerated given the benefits of starting a family early when life expectancy is relatively short. Parent-offspring conflict theory may also be useful in understanding why early marriages may be incentivized for parents if not daughters, especially in the context of marriage payments i.e. higher bridewealth or lower dowry for younger brides. Yet, in many cases, early marriage appears driven by female choice (including via elopements against parental will), without clear costs to wellbeing, questioning the notion that women’s agency is restricted. Context is king.

Frankly, without lived experience of societies where such practices are common, let alone the gendered power dynamics of heterosexual marriage and childrearing, I also remain cautious to weigh in on debates about what is good and bad for women. I’ve tried to strike a balance in presenting our research findings as objectively as possible, while being open to rethinking my own assumptions and those of my paradigmatic training. Key here has been a pivot into qualitative methods (spearheaded by Susan Schaffnit), prioritizing the voices of community members deemed at risk, along with collaboration with Tanzanian scholars at the National Institute for Medical Research, especially Mark Urassa, and Joyce Wamoyi.

So, are large spousal age gaps bad for women? Evolutionary psychologists have tended to focus on the mutual benefits of husband-older marriage: with women effectively exchanging youthful fecundity for the wealth and status of senior men. However, even early work in this tradition hints at the limits of this perspective. Kenrick and Keefe for example, report that, while American women find slightly older men attractive at all ages, as men get older they prefer relatively younger and younger women. Such divergent preferences are not mutually compatible.

Surveying Sukuma women living in a rural, but urbanizing community in northern Tanzania, our recent paper provides some potential answers, and raises new questions. Consistent with conflicting preferences, women routinely marry men older than their stated ideals. However, among the large majority married to older men, the age gap did not meaningfully predict self-reported depressive symptomology, autonomy in decision-making (a frequent measure of women’s empowerment), the likelihood of divorce, or reproductive success. While our ability to infer causal relationships is limited with cross-sectional data, these results suggest the magnitude of spousal age differences is of little consequence to women’s wellbeing or fitness – supporting neither a mutual benefits or a sexual conflict model.

Unexpectedly, we also found that marriage to a younger man, a rare arrangement in this community, was associated with relatively poor wellbeing for women. Qualitative findings indicate that such husband-younger marriages are socially shameful; suggesting costs of norm violation along with selection of relatively disadvantaged individuals into atypical marriages. This could come about, for example, if men with otherwise limited marriage prospects partner with older women who themselves are relatively disadvantaged prior to marriage.

These results correspond to our wider findings on polygyny and child marriage, both of which show little evidence of being directly costly to women’s wellbeing, more obviously predicted by factors like access to education and health services. In fact, in past studies we have shown that marrying polygynously is associated with relatively superior child health and food security compared to monogamous marriage; and brides under the age of 18 years report greater decision-making autonomy and community respect than their unmarried peers. As illustrated above, our results also confirm the role of social norms and norm violation in defining feasible options for girls and women. Related research shows that gender norms favoring male authority are represented and reinforced via Sukuma songs about marriage.

On the one hand, knowing that certain marriage practices do not predict poor wellbeing when girls and women are contrasted within a community usefully steers us away from simplistic interventions that might punish the families involved. We have argued, for example, that criminalizing marriage under 18 years may be damaging for female adolescents by limiting options, unless such interventions are also effectively combined with policies addressing the vulnerabilities experienced by those delaying marriage, i.e. exposure to risky sexual behavior, premarital childbearing, and negative social judgements of unmarried women.

Our research cautions against portraying ‘traditional’ marriage practices as the lynchpin, that once unlodged will dismantle patriarchy. But leaves open the possibility that community-wide changes in these practices may nevertheless have positive impacts for women by disrupting wider social norms.

On the other hand, it would be erroneous to imply that our results imply marriage arrangements such as large spousal age gaps are harmless. Critical here is the realization that a girl or woman may opt for a certain marital arrangement as the best available alternative, but the fact that her option set is remarkably limited by wider cultural norms can itself be considered an indirect act of coercion. These instances, perhaps best considered forms of ‘structural violence’, are less often considered within adaptationist frameworks that certainly model sexual conflict, but more often via theorizing about opposing individual optima and emergent strategies, rather than tackling more systemic forms of oppression. The challenge ahead is to disentangle to what extent specific marriage practices are best understood as the product of patriarchal regimes, or themselves a root cause of gender inequality.

Our research cautions against portraying ‘traditional’ marriage practices as the lynchpin, that once unlodged will dismantle patriarchy. But leaves open the possibility that community-wide changes in these practices may nevertheless have positive impacts for women by disrupting wider social norms. We need more social scientists, including evolutionary-minded scholars, with their keen adherence to the importance of context and variation, to apply themselves to these tricky questions. Fundamentally, the question is not if, but when and where, polygyny, early marriage and large spousal age gaps can be harmful to women. We also need to be mindful to make sure that investigation into these sensitive topics is fully inclusive of researchers and communities in the Global South. Above all, as argued recently by Akurugu and colleagues “Gender activism needs to be sensitive to contextual norms and respectful of the ‘oppressed’ subjects of ‘liberation”

Read the paper: Lawson DW, Schaffnit SB, Hassan A, & Urassa M. (2021). Shared interests or sexual conflict? Spousal age gap, women’s wellbeing and fertility in rural Tanzania. Evolution and Human Behavior. 42: 165-175

David Perrett is a professor at the University of St Andrews and the winner of the 2020 Lifetime Career Award for Distinguished Scientific Contribution, which he will receive at the next HBES conference. Carlota Batres, an assistant professor at Franklin and Marshall College and one of Dave’s former PhD students, interviewed him for HBES.

Carlota: Can you tell us how your academic journey started?

Dave: As a kid I grew up in the country in a house between two sloping fields. A small stream ran through the garden and churned up stones full of fossils (shells and trilobites) which I found captivating. My brother pitched a disused aeroplane nose cone (somehow acquired by my father) over the stream so I could sit inside and study life in the mud (e.g., bloodworms and what ate them). This gave me a head start in thinking about evolution and ecology (though those words were not in my head). In my teens, I had inspirational biology and chemistry teachers and took to being a swot.

Carlota: Out of your 300+ publications, which project has been the most fun for you and why?

Dave: Transforming faces lets you to poke fun at villains, politicians and friends, all in the name of science. A newspaper cheered us with the heading “Boffins help Thatcher’s image fade away” when we morphed the prime minister to a challenger.

Carlota: Rumor has it you are retiring. Is this true? If so, what will you miss the most and what are you most looking forward to?

Dave: I am now on a 20% contract but still work most days. I already miss the privilege of planning experiments and analysing experimental data with smart researchers. Exploring data hot off the press is like opening a present, you might guess at what’s going to be inside but the reality of what you find is always more interesting. The young brains that came through the lab invariably brought humour and curiosity, making the work environment happy and stimulating. I tried to keep in mind that the process of science should be enjoyable and is more important than any result. Our lab was open plan which meant I could drift from one colleague to another and disturb all; the proximity and atmosphere kept us all on our toes.

I now look forward to leisurely breakfasts watching garden visitors (predominantly birds). They come each with their own schedule and tricks: squabbling greenfinches, blackcap bullies and feisty robins.

Carlota: You change your hair color often, and many times have several different colors at once (e.g., purple, green, blue). Is there a method to when and what colors you dye your hair?

Dave: There several drivers of colour use. At northern latitudes you need something to cheer you through the long grey months. The coloured appearance of my wife, Anne, and myself also helped mutual recognition (I am fairly face blind). Initially a change in colour would justify new additions to our wardrobe.

The academic system embraces eccentricity so I treated appearance as a kind of handicap; if people took me seriously despite how I looked then what I was doing must be OK. It is a mark of independence or stupidity, or both. I have encountered disapproval only 2 or 3 times (e.g., looking for a place to stay in Niagara Falls, a door was closed in my face). I think people are often amused, so if our eyes meet there is a positive expression to react to.

Carlota: Can you tell us about your unique exercise and eating routines?

Dave: Hmm! An earlier me loved to run most days and explore wherever I was (i.e. get vaguely or actually lost). The best times were running at Pete Henzi and Louise Barrett’s study site in the Karoo semi desert among giraffes and antelope, hoping that 4 of the big 5 would take no notice of me. Running kept me warm at -24°C, when snow lined my eyebrows and an icicle hung from my nose, and running cooled me while lapping small sweaty tropical islands.

I rationalised that the exercise needed fuel so took to eating 4-5 meals a day. Vinet Coetzee taught me about 2nd breakfast during her PhD in the lab. Since then I have disgusted/amused staff in the coffee room eating lentils or cold beans topped with chilli as the perfect mid-morning pick-me-up. Now diet is just entertainment as I eat similarly but have had to stop running through injury.

Carlota: What is something people at HBES would be unlikely to know about you?

Dave: I failed English Language O Level and have been so lucky to have had Anne using her talent and training to check every work word I’ve put my name to. We enjoy flowers and have a garden with special places for poppies (every type from the blousy Shirley to the sacred Himalayan blue). Creepy crawlies are just as important to us, so we use a UV night light to attract moths in our garden and go on fungal forays turning up oddities like a red club fungus that eats insects.