Epigenetic inheritance
in the first trimester, the baby was born at a normal weight. However, when those babies (daughters) grew up, they were more likely to develop obesity and, in turn, have heavier-than-normal babies themselves. In contrast, if a mother was malnourished only in the third trimester, the baby was born underweight, but those daughters later had children of normal weight. This illustrates that although a father's sperm can impart a tiny epigenetic message, such as ‘stress’ or ‘store fat,’ the mother's body is the universe in which the baby develops. Her health can easily override that small paternal message. The second major limitation is a natural process called epigenetic reprogramming. This is like a great ‘reset button’. Right after a sperm has fertilized an egg, the embryo deletes almost all of both parents' epigenetic tags. This is a necessary fresh start so that the new embryo can develop into all sorts of cells. As Carey states, this means the few epigenetic tags that survive this process even more special and precious. The majority of them are erased, so only a very narrow set of a father's epigenetic messages will end up surviving. This stops every single life experience from being passed down, which would cause chaos. Finally, while it is quite straightforward to demonstrate epigenetic inheritance in lab mice, it is much more challenging to show it definitively in humans. To show true transgenerational inheritance in humans, you would have to prove that a father’s stress affected not just his offspring (who might share his stressful environment), but also his grandchildren. That’s a very long and difficult study to do, though the Överkalix study hints at it. The new science of epigenetics shows us that a father's life, what he eats and how stressed he is, can cause real, biological changes in his sperm. These changes, through DNA methylation, histones, and small RNAs, can then influence the health of his children, their risk for obesity, diabetes, anxiety disorders etc. While natural mechanisms like reprogramming cancel out most of the signals in a father’s sperm, a father's health is more (possibly) influential than we used to think. References Carey, N. (2012) The Epigenetics Revolution: How Modern Biology is Rewriting Our Understanding of Genetics, Disease and Inheritance . Icon Books Dias, B. & Ressler, K. (2014) ‘Parental olfactory experience affects behaviour and neural structure in subsequent generations’, Nature Neuroscience 17(1): 89–96. Ng, S. et al. (2010) ‘High-fat diet in father' s programs β-cell dysfunction in offspring’, Nature 467(7318), 963– 966. Pembrey, M. et al. (2006) ‘Sex-specific, male-line transgenerational responses in humans’, European Journal of Human Genetics 14(2): 159–166. Rando, O. & Simmons, R. (2015) ‘I'm eating for two: parental dietary effects on offspring metabolism’, Cell 161(1): 93–105. (A good review article that summarizes a lot of the diet evidence.) Rodgers, A. et al. (2015) ‘Paternal stress exposure alters sperm microRNA content and reprograms offspring HPA stress axis regulation’, Journal of Neuroscience 33(21): 9003–9012.
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