Epigenetics may be the grand unified theory of the nature vs. nurture debate, and the most significant advance of the last decade for understanding human nature and evolution in general. And this article is an excellent primer.
Basically, Epigenetics is the field of study that analyzes gene expression and not just the chromosomal properties of genes. Of course, each cell contains the chromosomal instructions for each and every of the over two hundred varieties of cells of the human body. Apparently, epigenetic regulation occurs on a cell-by-cell basis through methyl groups or proteins that are attached to each cell like a little bobble or ornament. Think of it as a chemical nametag that differentiates each cell by telling it which genes to express and which to silence.
Epigeneticists are now experimenting with twins and the like, and have found that twins become less biologically similar over time, and the same may be true in reverse: adoptees may exhibit traits of their adoptive families by virtue of the environmental influences on gene expression. Considering how similar our genes are on an overall basis, it makes perfect sense that human development would be influenced by the unique environmental factors that provide more fertile ground for differentiation.
Perhaps most surprisingly, it seems as though epigenetic traits may be passed on to future offspring because which genes are expressed are changed on a cellular level by environmental factors. If true, this would seem to call for a revision to the old natural selection dogma that mutation is all that matters. It would also (more poetically) bring Lamarck back from the metaphorical grave Darwin dug for him.
Indeed, the parallels to the development of Newtonian/subatomic Physics are striking, and it might take an Einstein to communicate the implications of this theoretical revolution effectively. Of course, Darwin didn’t know anything about genetics himself, and only spoke of adaptation in order to survive, so his theories are not to be thrown out the window. Surely epigenetics is simply one alternative and viable pathway for Darwin’s theory to express itself. There is a natural selection and survival of the fittest for metaphors too, of course.