Deconstructing nature-vs-nurture charts

By Felix Salmon
September 2, 2009
Greg Mankiw sparked a blogospheric resurgence of the nature vs nurture debate, Brad DeLong and Tyler Cowen weighed in with very different views of the empirical data. Tyler featured an extremely provocative graph, and I waited for someone, maybe Yglesias, to respond.

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After Greg Mankiw sparked a blogospheric resurgence of the nature vs nurture debate, Brad DeLong and Tyler Cowen Alex Tabarrok weighed in with very different views of the empirical data. Tyler Alex featured an extremely provocative graph, and I waited for someone, maybe Yglesias, to respond.


In the end, the expected take-down came from finance whiz Mike Konczal, solidifying even further his status as the Italian Vogue of the econoblogosphere: the best that there is, read by everybody who matters, if nobody else. Mike drilled down deep in to the dataset used to generate this chart, and found:

  • The adoptees are four years younger than the non-adoptees: 28 years old, on average, compared to 32 years old. These are years in which most people’s income rises substantially.
  • 70% of the adoptees are female, compared to only 39% of the non-adoptees. Females earn less than males, and male heirs might well be better at inheriting their father’s income than female heirs.
  • The family income of the non-adoptees was $61,000 per year; the family income of the adoptees was only $42,000 per year.
  • The income of both adoptees and non-adoptees was measured by asking their mother how much she thought they were earning. Which obviously affects reliability.

On top of all that, there are racial issues which may or may not be relevant: the adoptees, in this group, were generally of a different race than their adopted parents. Put it all together, and the most we can learn from Tyler’s chart is, as Mike puts it, that there are “a lot of interesting questions for follow-up”. We certainly shouldn’t treat the study as showing anything solidly empirical.

Update: Karl Smith weighs in.

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9 comments so far

Felix, that was Alex’s post, not mine…

Posted by Tyler Cowen | Report as abusive

This gets me thinking about genetics and income distribution…

Here’s a question for folks in favor of uber-progressive tax regimes to level the income/wealth playing field.

Let’s say the amount of genetic “IQ” material is fixed for all of society and that genetics advances have made it easy to identify and allocate IQ genes.

Question: Would you support an IQ tax of, say 5%, that takes a little IQ (eg genetic material) from folks with the best IQ genetics to help out those that are less fortunate? (Just for fun, assume that taking the genetic material from the “haves” makes them 5% less smart.)


the way i understand economics, being ‘well off’ has more to do with propensity to save than a persons’ intelligence quotient.

the pelosi liberal types want to feed you that nickel and dimed poo with an arogance of eugenics. hard work still pays off. stop having kids and eating mcdonalds- too expensive, a box of pasta still cost less than a buck

Posted by dvictr | Report as abusive

Reading some of the comments on the links, I’m surprised at how many people equate IQs with being smart. The IQ is a measure of an individual’s ability to learn. A hard working student with a lower IQ will be much more successful in school and life than a lazy student who could learn easily with a little effort.

Felix, look at the graph carefully! Mike’s revisions make the difference in the income effect on biological versus adopted children even *larger*. Note that across the range the income of biological children triples, from 30k to nearly 90k, while that of adopted children increases negligibly from 50k to 60k.

Mike also doesn’t seem to know that there are dozens of studies with different data from different countries showing the same thing – I just picked a particularly easy study to understand.

Again? Nurture beats nature as was proven long ago (Lerner, Lowe 1953)

Posted by Dave | Report as abusive

My neighbors adopted a little girl knowing she would never work or live independantly. No amount of nuture was ever going to overcome her severe disabilities.

While nurture certainly matters, it cannot compensate for nature’s victims. If the number of adoptees in the sample who are “special needs” children outnumber the number of “special needs” children in the non-adoptee sample, it could dramatically impact the numbers in the chart.

Posted by Brad Ford | Report as abusive

Is age at adoption considered? I’d think there’d be a possibility of subtle long-lasting psychological issues with a child adopted after infancy, especially if they bounced among foster parents.

Self-confidence might be lower, for instance.

Posted by Jon H | Report as abusive

Taller people earn more. so do attractive people. Also physics professors make less than sucessful builders or salesmen, though not higher in IQ.

Posted by alibeamish | Report as abusive
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