Giving life is a miracle, but for our body, it is also a costly investment. A massive study led by the University of Helsinki has just confirmed a fascinating hypothesis of evolutionary biology: our organism constantly decides between reproducing and repairing itself. And according to researchers, there is a “comfort zone” for longevity, located between two and three children.
The resource dilemma: the “disposable soma” theory
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Why would the number of children influence the speed at which we age? The answer lies in the disposable soma theory. According to this concept of evolutionary biology, each organism has a limited stock of energy and time.
When a massive part of this energy is mobilized by reproduction (pregnancy, breastfeeding, education), it is mechanically removed from the maintenance and repair mechanisms of our cells. “When a large amount of energy is invested in reproduction, it is taken away from maintaining the organism, which reduces life expectancy,” explains biologist Mikaela Hukkanen.
The twin study: an implacable biological verdict
To eliminate genetic bias, the researchers analyzed data from nearly 15,000 womenall twins. They tracked the markers of their biological aging (the age of their cells in relation to their calendar age) and their mortality.
The results reveal a very clear “U” curve:
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The “large family” group (average of 6.8 children): These women present accelerated biological aging and a higher risk of mortality. The repeated effort of motherhood seems to have “worn out” the cellular repair mechanisms.
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The “childless” group: More surprisingly, this group also shows less favorable results. Here the disposable soma theory does not apply. Researchers suggest that pre-existing health conditions may be behind this dual correlation: reduced fertility and poorer long-term health.
Is there a “golden ratio” for longevity?
The study points to an optimal window. The lowest markers of aging and the longest life expectancy were observed in women who had two to three childrenwith pregnancies occurring between 24 and 38 years old.
It is interesting to note that women who had children very young also show signs of premature aging. From an evolutionary point of view, natural selection could favor rapid reproduction to ensure the survival of the species, even if it means sacrificing the long-term health of the mother. However, for this specific group, lifestyle (alcohol, BMI) appears to play a more important role than the pure biology of pregnancy.
A sustainable biological footprint
« Our results show that lifestyle choices leave a lasting biological imprint, measurable well before old age.e,” underlines Miina Ollikainen, epigeneticist. This work is not individual health advice – parenthood also brings numerous psychological and social benefits – but it offers new insight into the way our reproductive history shapes our end of life.
The human body is a rigorous accountant: each resource allocated to the next generation is one less resource for our own cells. A fragile balance where the life of tomorrow is paid for, literally, with the years of today.
The study is published in Nature Communications.
