The scientists focused on one specific histone modification called H3K27me3. This "epigenetic mark" represses genes — it helps keep them switched off. To disturb it, the researchers made the worms temporarily express a mutated form of the H3.3 histone, which scrambled the normal distribution of H3K27me3 along the DNA.

The consequences were immediate and severe. Fertility dropped from roughly 300 offspring per parent to 100, and in some cases to just 50. Crucially, this damage was not written into the worms' genes. The descendants were genetically normal, so the team could watch what happened to gene regulation and fertility in each following generation.

What did they find?

The effects refused to go away. "Surprisingly, we found that the effects did not disappear when the initial trigger was gone. In the descendants, which were genetically normal, the changes in gene regulation and the fertility defects persisted for at least 15 generations," said Isa Özdemir and François-Xavier Stubbe, a Ph.D. student and a postdoctoral researcher in Steiner's group and co-first authors of the study.

The team then traced how this memory is kept alive. They identified two mechanisms acting one after the other:

• An establishment mechanism, which sets up the new epigenetic state right after the initial disruption.
• A maintenance mechanism, which preserves that state as generations pass.

"Our results show that maintaining an epigenetic state relies on a succession of specialized mechanisms, rather than on a single process," Özdemir and Stubbe explained.

Why does it matter?

The findings point to a form of heredity that operates independently of DNA sequence. "A temporary disruption of gene regulation can leave a lasting and transmissible imprint, even though the genetic change that initially caused the disruption has disappeared in the descendants," Steiner concluded. "This type of inheritance could represent an additional mechanism allowing organisms to respond and potentially adapt to changing environmental conditions."

As with any laboratory result, caveats apply. The experiments were done in worms, not humans, and the researchers artificially induced the epigenetic disruption rather than observing it arise naturally. Whether similar multi-generation epigenetic memory works the same way in other organisms remains an open question.

Even so, the study gives one of the clearest demonstrations yet that biology can pass information between generations through chemistry layered on top of genes — a memory written not in DNA, but around it.