It is the combination of inheritable and quickly adaptable, that makes epigenetics such an important finding.
Some of the time it's the code (nature), sometimes it's the data (nurture).
Seems to me DNA is kind of like a recipe for beer, and on a humid day the beer comes out a little different with the same recipe. But if you go back to the original weather the beer will come out the same.
So if you sent a Dutch couple of today back in time to the diet and environment of 50 years ago, their kids would be the height Dutchmen would have been 50 years ago, since the DNA and environment are the same. Nothing else changed inside the Dutch that would make their kids taller, and the change in height isn't something that is 'heritable' through other than DNA.
What makes such a thing interesting is if it persists through cell divisions, and especially interesting if it is passed down to the next generation. And it turns out that, surprisingly, such things exist.
It does?
> Epigenetic studies show that genes alone do not determine form and function,
Of course genes alone do not do that - that's the whole point of the nature-nurture debate, and the fact that most things are a mix of nature and nurture. We already knew a long time ago that genes alone do not determine form and function.
> but that the cellular environment matters in making people who they are as biological and social beings.
That also isn't new. Of course the cellular environment matters in making people (for example, fetal alcohol syndrome is a clear example of that, way before epigenetics).
The fascinating thing about epigenetics is something else entirely. It is that there is inheritance of traits via a path that is not DNA. This is incredibly important and interesting, but was not what showed us that genes do not determine everything about organisms, we knew that long before. In other words, we already knew non-genetic factors determined how organisms are formed and behave, but epigenetics showed us that those non-genetic factors can be inherited.