Shared environment (as constructed) is back

I have discussed in the past the conundrum between what the data says about parent's affect on child development (it is all in the genes and in the non-shared environment and parents are a trivial impact) and my personal sense that parental influence is more important than the data indicates.

Children’s personal characteristics are the product of three sources: shared environment, non-shared environment, and parents’ genes.

and

More suggestive than conclusive

I am quite keen on evidence-based decision-making. The tension between what I instinctively believe to be true versus what the data indicates to be true has been challenging. From More suggestive than conclusive:

As an example, for years I would have argued with reasonably good evidence that parental influence, and not just genes, were instrumental in childhood outcomes. I accept, with some asterisks, the evidence that genes are a stronger predictor of childhood outcomes than we used to accord. But many take a strong position that all childhood outcomes are due to genes and non-shared environment (outside the home); parents don't matter.

I natively want to believe otherwise but I can see the evidence as it exists. However, I suspect we are not defining the boundaries between shared environment and non-shared environment with great enough specificity and we are not paying enough attention to developmental sequencing.

More specifically, I suspect parents actually do exercise more substantial influence over their children's life outcomes, not via the time spent in the home (shared environment), but rather in all the attendant decisions about a child's environment. Where they live, the neighbors to whom they are exposed, childhood friendships that are encouraged or discouraged, school attended, church community involvement, sports, etc. Parents create, consciously or unconsciously, a developmental ecosystem around a child, most of which parents may not be, and usually are not, involved in directly. My suspicion is that by developmental ecosystem choices, parents are in fact shaping their children's life outcomes but doing so indirectly.

I think the level of our research sophistication is at this point still undeveloped and that when we begin taking into account indirect parental influence, we will find, counter to the current research, that in fact, much of the variance in life outcomes will be attributable to parental decision-making.

Is that motivated reasoning or is it rationalizing away from the nascent evidence. No way to know at the moment but we will know in time.

Well, for my piece of mind, perhaps the time is approaching. There is now evidence, still genetic evidence, suggesting that parental influence might indeed be functioning in the fashion I describe above. From You Are Shaped by the Genes You Inherit. And Maybe by Those You Don’t. by Carl Zimmer.

Dr. Kong wondered if other researchers had missed something very important. “It suddenly occurred to me that part of this effect could be coming through the parents,” he said. “And then I got obsessed with the idea.”

Children, after all, get their genes from their parents. It was possible, Dr. Kong reasoned, that genes could influence how far children got through school by influencing their parents’ behavior rather than the actions of the children themselves.

Dr. Kong was well placed to test that idea. DeCode has genetic records for many of the island’s 338,349 residents, including many pairs of parents and children. And among the questions that DeCode had asked its subjects was how many years of school they completed.

In the new study, Dr. Kong and his colleagues used a new method to measure the influence of genes on education. They didn’t inspect individual variants to see if each clearly had an impact; instead, they added up the influence of hundreds of thousands of variants in people’s DNA, even if they had a very weak influence at best.

The researchers compared 21,637 Icelanders to their parents. The parents, of course, passed down one copy of each of their genes to their children. Some of these might be related to educational attainment, and some not.

But Dr. Kong and his colleagues focused their attention on variants carried by parents but not passed to their children. These variants, the researchers found, predicted how long the children stayed in school — even though the children had not inherited them.

Any single variant in the parents had a minuscule effect on the children’s education. But combined, the researchers found, the untransmitted genes had a significant impact. Their combined effect was about 30 percent as big as that of the genes that the children actually inherited.

Animal researchers have amassed a wealth of evidence showing that animals are influenced not just by their own genes but by the genes of their parents. Credit Brianna Soukup/Portland Press Herald
“The direct genetic effect is quite a bit smaller than what people thought,” said Dr. Kong, who now a professor at the University of Oxford.

How can that be? Dr. Kong speculated that the genes carried by parents influence the environment in which their children grow up. “Variants that have to do with planning with the future could have the biggest effect on nurturing,” he said.

Dr. Harden expected that genetic nurture would turn out to be a very complex phenomenon. “My intuition is that it’s not any one thing, but a constellation of things,” she said.

We'll see. I certainly would like to see parental actions reassume their importance in child life outcomes. Genes are important. Non-shared environment is important. Shared environment (parents) now are back in the game.