A new study reveals that the trade-off between reproduction and longevity becomes evident only during harsh environmental conditions, such as famines. Researchers analyzed records of over 4,500 Finnish women across 250 years, finding that those who gave birth during the Great Finnish Famine of 1866-1868 had their life expectancy reduced by six months per child. This supports the disposable soma hypothesis but highlights its context-dependency.
The disposable soma hypothesis posits that ageing results from evolution prioritizing reproduction over bodily maintenance, diverting energy from DNA repair, illness resistance, and organ upkeep. This trade-off is thought to affect women more due to the demands of pregnancy and breastfeeding, which require hundreds of extra calories daily.
Previous studies on whether more children correlate with shorter lives have yielded mixed results, with some showing support and others none. "It is very difficult to disentangle what is just correlation [between having more children and a shorter life] and what is the underlying causation, unless you have a good, big dataset that covers several generations," says Elisabeth Bolund at the Swedish University of Agricultural Sciences.
Euan Young at the University of Groningen and colleagues hypothesized that the reproductive cost varies by environment. "In good times, this trade-off isn’t really visible. The trade-off only becomes apparent when times are tough," Young explains. To test this, they examined parish records of more than 4,500 Finnish women over 250 years, including the Great Finnish Famine from 1866 to 1868.
The analysis found no significant link between the number of children and lifespan for women outside the famine period or who did not bear children then. However, for those who did, each child reduced life expectancy by six months. This echoes a prior Quebec study on stressed pre-industrial populations but ties it to a specific catastrophe.
"This very large dataset makes it feasible to account for confounding factors [such as genetics and lifestyle factors]," Bolund notes. During famine, lacking caloric intake forces the body to lower basal metabolism, impairing health and shortening life. This may explain patterns in lower socioeconomic groups historically.
Today, with fewer children—averaging 1.6 births per woman in the US—the threshold for such costs (over five children in a Utah study) is rarely met. Women now outlive men by about four years in the UK (for 2021-2023 births), partly due to reduced reproductive burdens, though smoking, alcohol, and chromosomal differences also play roles. Further research is needed on sex-specific ageing factors.
The findings appear in Science Advances (DOI: 10.1126/sciadv.adz6422).