DNA? Nurture? What makes us what we are?

Yesterday I read the following short article by Robert Plomin, an American psychologist and geneticist best known for his work in twin studies and behaviour genetics:

Parenting myths and the DNA revolution

I recommend people read this before proceeding further, it is only very short. (Update 11/8/22 I note that the whole article is no longer available!  Using wayback machine, try this).

My own position is that the notion that we are born blank slates and it is purely the environment that makes everything we are, is preposterous.  I briefly touch on this issue here.  I should stress, though, that our environment does, of course, shape and mould our behaviour.  This is often a persona that one learns to put on in order to be accepted by others.  But also, as we grow older, most of us (but not everyone) can acquire genuine empathy and compassion as a result of their interactions with others.  However, the notion that everything we are -- all our interests, our treatment of others and so on -- is wholly due to our environment, I find extraordinarily implausible.   


The article states that:

 "children growing up in the same family with the same parents are no more similar than if the children were raised in different families".

So, in other words, regardless of whether 2 children are brought up in the same family or whether each of them are brought up in different families, the author is claiming that this will not affect their personalities.  This is compatible with my own position since, though I think we can change by acquiring empathy and so on, this is not something that can easily be taught.  Moreover, this is largely only applicable once one reaches adulthood in any case.

The author states that his fifty years of research shows that:

inherited DNA differences account for about 50% of the differences between children for all psychological traits.  

So what about the other 50% if it is not due to the environment?  This is the interesting part.  The author says:

Following years of research trying to identify the environmental factors that make children in the same family different from one another, I conclude that they are mostly idiosyncratic, random factors over which parents have little control—in a word, chance. 

Of course, saying that the other 50% of all psychological traits is due to "idiosyncratic, random factors" is to say precisely nothing.  He is effectively saying, I have no idea what accounts for the other 50%, it beats me.  In other words he's floundering, flummoxed, unable to come up with any conceivable mechanism for the other 50%.

What seems to me to be happening here is that the author presupposes that we are purely material beings and hence it can only be the environment or our genetic makeup or some combination thereof, that can possibly explain the entirety of our psychological traits.  It seems that virtually the entire academic community are in this straitjacket, confining their thoughts to only those possibilities consonant with a naturalistic metaphysic. Virtually all of them believe that our nature is fixed by something external to the self -- whether it be the environment, genetics, or some combination of both. They are implicitly assuming that everything we are is simply a result of impersonal material processes.

This contradicts our commonsensical conception of the self that I have articulated in many of my blog entries, two very recent ones being here and here.  I regard it as a mistake to suppose that anything material -- whether genes or environment -- has to make us what we are. What we are, our essence, is just a fundamental fact not capable of further analysis. At best we might say we self-actualise our own essence. We make ourselves what we are. That is, we self-cause our own nature.

For me, the fact that his research has been unable to account for 50% of all psychological traits is entirely unsurprising, and indeed, to be expected.  It's like being surprised that people who have imbibed the same amount of alcohol don't all act the same.  Yes, they might all become more gregarious, more impulsive, and so on.  But that's just an influence on their distinct essences.  I suspect the genetic component of us plays a similar role.