Epigenetics: Experience Writes on the Genome
Conrad Waddington / Michael Meaney · 1942
"Epigenetics shows experience can leave chemical marks on DNA that change gene expression without changing the code — and some marks, via careful animal models, appear responsive to stress, nutrition, and care."
Waddington coined 'epigenetics' in 1942 for how the same genome produces different outcomes by context. Meaney showed in the 2000s that rat pups licked more by mothers grew different stress responses because of a chemical mark, not a different gene.
Methyl groups and histone modifications act like annotations on the genome — turning volume up or down on existing genes. In rodents, variation in maternal care methylates the glucocorticoid receptor promoter, shifting HPA-axis calibration for life; diet and toxins do similar in specific windows. In humans, evidence is largely correlational and modest-effect — popular coverage overclaims 'trauma is inherited' — but the mechanistic principle stands: environment biases which parts of the inherited system get expressed.
What does epigenetics demonstrate about gene-environment interaction?
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The explanation above is written with AI assistance. These are the originals — go to them to check it.
- EpigeneticsWikipedia
Mirror Neurons & Embodied Simulation
"Rizzolatti's team found neurons that fire both when a macaque grasps and when it watches another grasp — suggesting understanding others is not abstract inference alone but embodied simulation of their actions and intentions."