The standard sperm-meets-egg story posits that sperm cells are hardly more than bundles of shrink-wrapped DNA with tails. Their mission is simple: Deliver a father’s genes into a mother’s egg for sexual reproduction. Just about all other aspects of a developing embryo, including its cellular and environmental components, have nothing to do with dad. Those all come from mom.
But nearly two decades of studies from multiple independent labs threaten to rewrite that story. They suggest that dad’s gametes shuttle more than DNA: Within a sperm’s minuscule head are stowaway molecules, which enter the egg and convey information about the father’s fitness, such as diet, exercise habits and stress levels, to his offspring. These non-DNA transfers may influence genomic activity that boots up during and after fertilization, exerting some control over the embryo’s development and influencing the adult they will become.
The findings, so far largely described in mouse models, could end up changing the way we think about heredity. They suggest “that what we do in this life affects the next generation,” said Qi Chen, a reproductive and developmental biologist at the University of Utah Medical School who is among the pioneers of this research. In other words: What a father eats, drinks, inhales, is stressed by or otherwise experiences in the weeks and months before he conceives a child might be encoded in molecules, packaged into his sperm cells and transmitted to his future kid. The researchers have largely zeroed in on RNA molecules, those short-lived copies of DNA that reflect genetic activity at a given time.
It’s a tantalizing notion. But the mechanistic details — how experience is encoded, how it’s transferred from sperm to egg, and whether and how it affects a developing embryo — are not easy to unpack, especially given the challenges of conducting research in human subjects. For this reason, and because of the potentially textbook-rewriting implications of the findings, researchers, including those spearheading the work, are cautious about overselling their results.
Colin Conine has shown that RNAs packaged in sperm alter gene expression in mouse embryos, pointing to a pathway by which a dad’s choices can epigenetically affect his offspring. Courtesy of Colin Conine
“It’s still very hand-wavy,” said the epigeneticist Colin Conine of the University of Pennsylvania Perelman School of Medicine and Children’s Hospital of Philadelphia, who has been trying to uncover the mechanics of how sperm RNA can contribute nongenetic information to progeny. Some elements of the story are clear, he said: Researchers have significant evidence that the environment can regulate sperm RNAs, that these molecules transmit traits to offspring and that they can regulate embryonic development after fertilization. “We just don’t have really any understanding of how RNAs can do this, and that’s the hand-wavy part,” Conine said.
But evidence keeps piling up. Most recently, in November 2025, a comprehensive paper published in Cell Metabolism traced the downstream molecular effects of a father mouse’s exercise regimen on sperm microRNAs that target genes “critical for mitochondrial function and metabolic control” in a developing embryo. The researchers found many of those same RNAs overexpressed in the sperm of well-exercised human men.
“This study shows that paternal exercise can confer benefits — enhanced endurance and metabolic health — to offspring,” said Chen, who was not involved in the study. “It’s a powerful reminder that many sperm-mediated epigenetic effects are deeply adaptive in nature.”
The possibility that a previously undocumented avenue of inheritance is at play is too important to ignore. That’s why the researchers are now hunkering down in their labs to trace out the molecular processes that would have to operate for a father’s here-and-now experience to be transferred as developmental instructions to his partner’s egg.
Epigenetic Avenues
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