Until recently, however, most evidence linking small sperm RNAs to environmental challenges and subsequent effects in offspring has been correlational. Attempts to pin down causality—by injecting RNAs directly into embryos—have often used far higher RNA concentrations than typically found in sperm. In fact, there was no proof that the RNA fragments even make it inside the egg.
But though puzzles remain, recent studies show that not only are paternal RNA fragments transferred to a fertilized egg, but also that they are capable of inducing changes in the offspring at the doses found in sperm.
Epigenetic effects
Researchers first noticed the intergenerational effects of paternal lifestyle back in the 1960s,
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