Welcome to an ongoing discussion of the causes of mental illness. I’ve been saying that bad parenting is not to blame.

Jo wrote this helpful comment:

Please cite additional researchers besides Judith Harris who support this research or who have found it to be true. I really think you are digging to support an opinion and leaving 98% of the peer reviewed data based research out of the loop. There have been a variety of studies that have controlled for genes that have found the environmental impact to be dramatic on the development of mental illness, especially personality disorders.

And Jo is entirely correct! Genetics account for roughly 50% of developmental impact and environment accounts for that other 50%.

But “environment” and “parenting” are NOT the same thing!

There’s an entire field of research called behavioral genetics, with tons of research to back up its Three Laws (from The Blank Slate, p. 373):

• All human behavioral traits are heritable.
• The effect of being raised in the same family is smaller than the effect of the genes.
• A substantial portion of the variation in complex human behavioral traits is not accounted for by the effects of genes or families.

Here’s what these laws mean:

• We inherit about 50% of “who we are” from our biological parents.
• We then learn the other 50% through experience.
• The experiences that shape us are NOT the ones we have at home; they’re the ones we have in the larger world of peers, school, community, etc.

Steven Pinker puts it this way:

A handy summary of the Three Laws is this: Genes 50 percent. Shared Environment (home) 0 percent. Unique Environment (peers, neighborhood, school, community, etc) 50 percent (or if you want to be charitable, Genes 40-50 percent, Shared Environment 0-10 percent, Unique Environment 50 percent).

He then added:

Keep this in mind and watch what happens to your favorite ideas about the effects of upbringing in childhood.

Now, of course, children need their parents in so many ways!

But children’s brains are built to distinguish relatives from non-relatives and to take sustenance  and protection from the former and learning from the latter. In the next post I’ll talk about Robert Trivers, the evolutionary biologist who figured this out.

But for now, consider our enormous brains and long childhoods. What are they for? For learning as much as possible about the world outside of the home, the environment every child is going to have to grow up into and live and compete in. Kids’ brains are designed to be relatively impervious to parental influence, because Nature doesn’t expect them to live at home forever.

To be continued!

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From Psych Central's website:
PsychCentral (March 17, 2010)

From Psych Central's website:
ADHD: Where does it come from? | ADHD from A to Zoë (March 21, 2010)

    Last reviewed: 17 Mar 2010