For centuries, humanity has sought to comprehend the aging process. The ancient Greek philosopher Aristotle theorized that aging correlates with the passage of time. The reduction of water necessary for bodily functions was his primary focus.

A contemporary concept known as the disposable soma hypothesis proposes that aging is the cost of reproduction; evolution, it argues, favors genetic replication above all else. This results in a fundamental trade-off. The substantial energy expended on having and nurturing offspring is often compromised by investments in DNA repair, disease resistance, and organ maintenance.

This idea is particularly relevant for women, who allocate more resources to reproduction through pregnancy and nursing than their male counterparts. However, when researchers examined whether women with more children had shorter lifespans, findings were inconsistent. Some studies supported the hypothesis while others did not.

“It’s challenging to extract clear correlations between childbearing and longevity,” said Elizabeth Bolland from the Swedish University of Agricultural Sciences, a professor not involved in the research.

Euan Young and associates from the University of Groningen in the Netherlands postulated that variations in reproductive costs depend on maternal environment, noting, “In favorable conditions, this trade-off is less apparent. It’s during challenging times that it becomes noticeable,” Young remarked.

To explore this hypothesis, researchers examined parish records of over 4,500 Finnish women spanning 250 years, including the era of Finland’s Great Famine from 1866 to 1868. Young highlighted how difficult times impacted reproduction and longevity.

They discovered that for women who lived before and after the famine, or those who had no children during that period, there was no notable correlation between child quantity and lifespan. Conversely, women who gave birth during the famine experienced a reduction in life expectancy of six months for each child born.

This research stems from a study released last year, which utilized a dataset from the pre-industrial populace of Quebec, Canada, tracked over two centuries. This previous work illustrated trade-offs in mothers likely to be in poor health or facing high stress, without evaluating the influence of specific environmental conditions.

In contrast, Young’s team emphasizes catastrophic events as factors that underscore these reproductive trade-offs. “This extensive dataset enables us to control for confounding variables,” he stated. “This study brings us closer to understanding causality without needing laboratory-controlled experiments,” remarked Bornd.

This investigation further endorses the energy demands of pregnancy and breastfeeding, which necessitate substantial additional calorie intake daily. During periods of starvation, women cannot acquire sufficient energy from food, which compromises their body’s “basal metabolism.” As a result, essential bodily functions may decelerate or cease, leading to deteriorated health and shortened lifespans, Young explained. This scenario clarifies why previous studies often identified these trade-offs predominantly in lower socio-economic groups, who typically reside in resource-limited conditions.

Bolland noted that this trade-off’s occurrence under particularly adverse circumstances, alongside a time when women usually had more children, may help clarify why women generally outlive men. In the UK, girls born between 2021 and 2023 are projected to live four years longer than boys.

In contemporary Western societies, reproductive costs have significantly diminished, with the average number of births declining drastically over centuries, as noted by Bornd. Consequently, it’s likely that very few women reach the stage where lifelong costs become evident. Bolland and colleagues noted in their study analyzing Utah’s historical population, that this threshold was only observed when women had five or more children. The average woman in the United States is now expected to have 1.6 children throughout her lifetime.

Therefore, other environmental factors may play a larger role in explaining the lifespan disparity between genders. For instance, men are generally more prone to smoking and tend to consume more alcohol, both of which influence longevity, according to Bolund. The current gap in longevity between men and women likely results from a mix of reduced reproductive costs for women relative to earlier historical periods, alongside differences in lifestyle choices.

Research also indicates that variations in sex chromosomes are significant. “Differences between the sexes extend beyond reproductive costs; thus, further research is essential to delineate how different factors impact sex-specific aging,” Young concluded.