Data and analysis are in the post below. This is more of a conceptual overview of the topic.
The the nature vs. nurture "debate," the pendulum has swung a bit too far toward the side of nature. Somewhere along the line, fans of behavior genetics â€” which is not to say the researchers themselves â€” convinced themselves that environments don't affect how we turn out as adults. At least, not in predictable ways.
There could be random environmental differences that affect development, like some molecule in the brain zigs instead of zags due to a quantum-level coin flip, and that winds up making the kid more extraverted instead of introverted. Or maybe there just happened to be a frightening dog on the way to school one day, and this traumatic experience makes the kid more fearful in adulthood. These are environmental effects, but they all boil down to chance and fortune.
What we tend to mean by "environmental effects" are when a parent uses corporal punishment, the child may wind up with violent tendencies in adolescence. But it could be that the parent had genetically influenced violent tendencies themselves, which expressed themselves in the use of corporal punishment, and expressed themselves in the kid as getting into pointless fights. Or perhaps the corporal punishment is an effect, rather than a cause of the kid's violent tendencies â€” natural-born hell-raisers induce parents to use tougher discipline than little wiener kids do.
What gets lost in this quibbling on and on is that what normal people usually mean by "environments shape development" is that some events have a much stronger impact than merely getting whipped with a belt. A small bruise will heal, but what about things that a kid is not going to be so resilient against, like growing up in a broken home, being molested, emotionally neglected, and so on?
In our neo-Dickensian world, such events are hardly uncommon. Recall this post which shows how increasingly common it is for white Americans to be growing up without both of their parents in the home â€” up to around 40% of those born in the late '80s.
To look beyond the individual level for how such kids are affected, a follow-up post looked at the loss of connectedness that children have when their parents divorce.
Now let's try to work both of these levels together. Depression and anxiety are found more often in children of divorce than in children from intact families. But depression isn't just a free-floating individual trait â€” it responds to how socially integrated you are. More connected environments might alleviate the sense of disruption and having been ripped out of the ground.
We can imagine all sorts of ways to define "more connected," and here I'll look at the outgoing, as opposed to cocooning, trend in social-cultural cycles. Children from broken homes must feel even more lonely and depressed when there's a larger climate of cocooning and atomization.
When folks are more out and about, milling around in public spaces, and neighbors are looking out for neighbors, those kids might not feel such a cripping loss when their parents split up. Compared to victims of helicopter parenting, kids in an outgoing climate have far greater support from their peers, and may also find surrogate parents throughout their neighborhood and peer group, to make up for their own dysfunctional parents.