Do you take after your dad's RNA? Growing evidence that sperm carries traces of a father's life experience
The classical understanding that genetic inheritance flows only through DNA has been challenged by a growing body of data over the past few years. According to research compiled by Ars Technica, sperm cells carry RNA molecules that bear traces of a father's stress, nutrition and traumatic experience; those molecules can transfer to the embryo at fertilisation and exert a transgenerational epigenetic effect.
The concept of epigenetic inheritance is not new; it has been observed for years, but it has been a contested area. In 2014 it was suggested that the elevated obesity rate among the grandchildren of women who lived through the 1944-1945 Dutch Hunger Winter might be linked to an epigenetic transmission. The biological mechanism for such findings was unclear, however. The discovery of sperm RNAs offers a concrete candidate.
A 2025 study by Anne Schaefer at the University of California, Davis showed that the levels of 27 different miRNA molecules in sperm cells of male mice under chronic stress had shifted significantly. When eggs fertilised by these sperm produced offspring, the pups showed marked differences in their stress responses; in particular they raised their cortisol levels more quickly and held them elevated for longer.
Human studies are at a more recent stage. A study published in early 2026 in Cell by the Karolinska Institutet found significantly different miRNA profiles in sperm samples from 174 fathers whose stress levels had been elevated in the previous 30 days. The lead author, Niclas Lindqvist, commented: "We are showing that stress can shift sperm RNA within days; that is a much faster biochemical response than we previously assumed."
Nutrition is another major driver. A 2024 Beijing study showed that a high-fat diet increased the abundance of small RNA fragments known as tsRNAs in the sperm of male mice. The pups born from sperm fertilising eggs had lower glucose tolerance and higher insulin resistance. Whether a similar mechanism operates in humans has not yet been examined, but the INCA institute in São Paulo plans to launch a 500-father cohort study in mid-2026.
The effect of trauma on sperm RNA is a more sensitive and ethically demanding area of research. A 2025 study completed at Mount Sinai Medical School found significant differences in five miRNA groupings in the sperm of 47 men diagnosed with post-traumatic stress disorder (PTSD), compared with 47 healthy men. Those differences suggest sperm RNA may serve as a long-term biochemical record of trauma.
The mechanism is elegant in that the transfer of RNA at fertilisation happens very quickly. The sperm cell delivers to the egg not only DNA but also small RNA molecules such as miRNAs and tsRNAs. Those molecules can shape gene-expression patterns during early embryonic development; the result is that the embryo acquires a particular gene-expression trajectory.
Researchers stress that caution is required in interpreting these findings. Maria Karpova, an epigenetics researcher at Yale University whom Ars Technica interviewed, said: "Most of these studies are done in mouse models. Human epigenetic inheritance is much more layered; we don't yet have the statistical power to leap from the available evidence to a clear-cut intergenerational causality."
Clinically, the findings could prompt new guidance in reproductive health clinics. Following the Karolinska study, several IVF clinics in Sweden have started offering would-be fathers a "sperm RNA optimisation" programme — typically a four-to-six-week regime of exercise, nutrition and stress management. There is no scientific evidence yet supporting the recommendations, but in principle sperm RNA can refresh in weeks.
In the longer term this research area also raises questions about how the classical understanding of evolution may need to widen. Lamarck's 19th-century theory of "inheritance of acquired characteristics" was rejected after Darwin; today's epigenetic data does not so much vindicate Lamarck as nuance the rejection, suggesting some Lamarckian effects may operate under specific conditions. As Schaefer says: "No one is saying Lamarck was right; but nature is more creative than we expected."