Epigenetics and Overclaiming

In a strict sense, epigenetics is happening all the time, and has to, or we would not have both bones and teeth in our formation. What people are usually talking about these days when the subject comes up, however, is the idea that what happens to Anne in her life affects her genes in a way that affects her daughter Andrea and Andrea's genes, and that this in turn her daughter Amanda and her genes, and then on indefinitely. It's loads of fun to talk about when sounding science-y, but there are just a lot of problems with it. 

Razib, who is a geneticist, has a primer on the subject showing its limitations. It is technical, dealing with methylation, histones and nucleosomes, and the difference between transgenerational and intergenerational trauma. Well past my previous knowledge and I had to double back and read again many times. Yet I think it is worth it, because 

Contrary to what headline writers and pop psychotherapists might like you to believe, thus far, epigenetics is terribly implausible as a factor in theories of human intergenerational trauma.

First, the effects being studied are usually the results of trauma, not "types of music Gramps liked to listen to." It is fair to allow that what "trauma" means to a cell might not be a famine or prolonged exposure to stress, but something more subtle like exposure to a novel chemical. Still, we are talking about large events here. Then also, we are usually talking about small effects per individual (though if spread over a whole population they might be significant). As exposure to both mother and fetus, and if it is a female fetus the exposure to her eggs as well, is what is grabbing attention and showing the most robust effects, it is important to note that this starts become definitional whether you call this epigenetics or just "exposure in the womb."

But effects are there and we are seeing some of it, so it's worth following up. There just isn't a lot of replication in many cases, largely because the natural experiments of famine in childhood or days of aerial bombardment during pregnancy cannot be summoned at will. 

Feel free to have a go at correcting - or modifying the emphasis of - Razib and especially me on this, as this is not at all my field.