Bryan Caplan  

How Nurture Works

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Hal Varian's Words of Wisdom... I plead guilty to plagiarism...

In a critique of Brink Lindsey, Arnold writes: "I think that my co-blogger would go ballistic over this 'nurture assumption' methodology." I wouldn't quite go ballistic, because there is solid evidence that growing up in a high-IQ home raises the IQs of adopted children. However, this IQ gain does not last. By the time he's 18, the correlation between an adoptee's IQ and the IQ of the family that adopted him is zero.

In short, parents are correct to think that they can change their children. Their mistake is to suppose that the change will endure. Instead of thinking of kids as lumps of clay that parents "mold," we should think of kids as plastic that flexes in response to pressure - and springs back to its original shape once the pressure goes away.


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COMMENTS (18 to date)
Giovanni writes:

That sounds like strong evidence in favor of innate or genetic IQ.

How do you explain how ethnic groups such as the Polish or the Irish used to have sub-standard IQ (relative to Jewish or English), and now that gap has largely disappeared?

Brad Hutchings writes:

Has anyone looked at high IQ individuals who were adopted into lower or average IQ homes?

Alex J. writes:

I think there was a study of a large number of Korean girls who were adopted in the US after the war.

Jim writes:

A link to evidence backing up Bryan's claim would be appreciated. I know there's a book on the subject, but presumably the authors have published something online or in journals too?

Troy Camplin writes:

My own IQ went up as I read more and more and put pressure on myself. It seems to me that if you want the IQ points to stick, you should teach your children to keep the educational pressure on themselves -- to love to learn -- and that mold will stay stretched out.

Jim writes:

Thanks KDeRosa, that's all interesting stuff, but unless I'm missing something it isn't quite what Bryan was talking about, and in any case the linked material suggests the science on this issue is far from settled.

KDeRosa writes:

The science is not yet settled, but the data is slowly accumulating.

TGGP writes:

Consider that the genetic component of intelligence may be preference. Once they're all grown up, you can't force them to learn if they don't want to. You can't permanently alter their preferences either, because evolution anticipates genetic conflicts of interest between parents and children and causes us to resist our parents attempts to change us (see Trivers on that).

Steve Sailer writes:

Okay, but say you can raise your kids' IQ by 10 or so points while they're children, but it eventually fades out -- that's really not so bad.

You can get them on a better track in life -- e.g., on the way to a career working indoors sitting down rather than outdoors standing up -- which they can proceed to enjoy for the rest of their lives. And they can more likely find a spouse from higher up the social scale to, so your grandchildren may have better genes too.

Steve Sailer writes:

Take a look at an old Steven Levitt column on how many more Canadian pro hockey players were born from Jan. to June than from July to Dec. -- those born earlier in the year had an advantage at youth hockey so they were picked for all-star teams and given special coaching etc, and it strikingly increased their chances of making the NHL.

So, by way of analogy, I could well think that having a high IQ upbringing could get your kid on the chance for success that he'd miss if he had a low IQ upbringing.

Rob Sperry writes:

I am not against the idea of IQ hereditability but are alternative interpretations that might account for part of the affect seen in the adopted twin studies:

Is it possible that people do not invest as much in adopted children or nurture them as much in general as their own children? (maybe due to evo phyc reasons, maybe lower expectations)

There is the the gestational period to consider both in terms of the positive impacts of good nutrition and medical care, as well as the bad impact of teratagens etc. (not much help for the nurture argument though)

The nurture side is poorly explored. There appear to be very few attempts to systematically study or develop practices that might increase intelligence in children. Its not like the adopted families were taking specific steps to try and develop the intelligence of their adopted children. So there may be specialized kind of nurturing environment and set of practices that can improve intelligence it just hasn't been discovered yet.

Sign language is one of the few things that seems to have good longitudinal data indicating that it can boost long term IQ. Are there any others?

There does appear to be at least anecdotal data suggesting that good training and practice can improve things like performance in athletics, music and mathematics ect. Zig and the Direct Instruction folks have shown that with a good system the learning of low SES kids can be greatly improved. I believe Zig originally started working with gifted children, but I haven't seen any large scale longitudinal data on the results of using his or other methods starting with gifted or even average children. Is anyone even aware of any attempts to do this?

KDeRosa writes:

There were lots of average and high-IQ kids tested in Project Follow Through. Their performance was accelerated as much as the low-IQ kids, but bear in mind that the lower performers tended to get more instructional time and the best teachers. See here and here.

Also, bear in mind kids' IQ is generally measured via some sort of achievement test IQ is much less malleable when IQ is measured by a highly g-loaded testing instrument, such as raven's Progressive Matrices. In Project Follow Through, students did not perform better on Ravens.

spencer writes:


As someone who has raised an adopted child and natural children the thing I miss in all this discussion of adoption is the fact that adopted children tend to have self-worth issues.

It is one of the great secrets of the entire adoption process that adopted children tend to have much more serious behavioral problems as teenagers.

it seems to stem from self-worth -- what was wrong with me that my mother did not want me?

How can you go into this discussion of adoption and IQ and completely ignore this issue?

TGGP writes:

It was my belief that in adoption studies the correlation between unrelated kids in the same households and related kids in different households was also compared to unrelated (adopted) kids in different households.

Steve Sailer writes:

We hear a lot from the adopted people who complain about being adopted but very little from the adopted people who don't, so we can get a distorted picture.

For example, consider perhaps the least psychologically troubled individual of the 20th Century, Pres. Gerald Ford, who wasn't outstanding at anything but was above average at just about everything. He said that when he was in the White House, he still fell asleep 10 seconds after he put his head on the pillow.

Well, President Ford was adopted. But, you don't hear about it much, because it didn't seem to trouble him.

Sam writes:

Ford was "adopted" by his stepfather. He was raised by his biological mother.

Tracy W writes:

As someone who has raised an adopted child and natural children the thing I miss in all this discussion of adoption is the fact that adopted children tend to have self-worth issues.
...
How can you go into this discussion of adoption and IQ and completely ignore this issue?

Well it depends what we are interested in. In the studies of the Korean adoptees, parents were assigned randomly to children (assuming they qualified to enter the programme), so whatever self-worth issues they had as a result of being adopted would not be correlated with their adoptive parents' characteristics.

What the Korean adoptees study indicates is that the richer parents did not manage to change their adopted children to make them earn more. If feelings of self-worth are relevant to this result, then we need to come up with some story as to why the adopted children of the richer parents had more significant problems with self-worth than the adopted children of poor parents, in order to offset all the material advantages rich parents could provide. This is hard to do.

Or in other words, the fact of being adopted could explain adoptive children's IQ/earnings being lower than biological children's. What it has problem explaining is that adoptive children's IQ/earnings are uncorrelated with their adoptive parents', while biological children's are. And in turn, what this lack of correlation implies is that having a permanent effect on children's outcomes is harder than we thought.

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