Last December, an unsettling Nature Neuroscience study found that mice who were taught to associate the smell of cherry blossoms with pain produced offspring who feared the smell of cherry blossoms, even if they had never been exposed to it before. We knew that the process was epigenetic—that it was not hard-wired in the permanent genetic structure of the mouse—but we didn't know exactly how it worked.
Earlier this week, a followup Nature Neuroscience study more clearly traced this sort of inherited trauma with RNA interference, and specifically with microRNA found in the sperm of mice. This trippy (and slightly disturbing) computer-animated video explains how RNA interference works, and the way microRNA fits into that process:
The more recent study also found that the multigenerational trauma carried on to at least the third generation. The implications of this are legion. Every fear, phobia, or aversion we have could potentially tap into a diluted form of the same sort of epigenetic trauma, passed down from parent to child across generations. Neatniks might inherit their cleanliness from an ancestor's plague; hoarders, from an ancestor's famine; the irrational bigotry of an unhinged racist might connect, on some unspoken level, to an ancestor's intertribal conflicts. If you're afraid of the dark, perhaps one of your ancestors almost died there. If you're afraid of water, perhaps one of your ancestors almost drowned.
It's easy to get reductionistic about this sort of thing, of course, and as epigenetics catch on as a field of study we undoubtably will. (We have a long history of turning exciting new fields of research into boring dogmas.) But epigenetics represent one more exciting area where everything we thought we knew about what it means to be human turns out to be, if not wrong, at least more complicated than we'd ever imagined.