The Inheritance of Education

Economix posted a graph showing a strong positive correlation between SAT score and parental income.  Greg Mankiw pointed out that the effect is unlikely to be purely causal because there may be an omitted variable bias, IQ for example.  Paul Krugman and Matt Yglesias both attack Mankiw and point to graphs showing that income matters for college completion and enrollment, respectively, holding various achievement scores constant.  Brad DeLong crunches the numbers on IQ and income correlation to estimate that half the effect is due to IQ and half to something else.

All this is good but none if it gets at the heart of the matter because there are a lot of way that heredity/genes could explain the income/education correlation; IQ is only one possible mechanism, personality (e.g. conscientiousness) is another possibility.

The type of evidence that we need to resolve this question is adoption studies.  Fortunately, such studies have been done and indeed I have presented the data before in my post Nature, Nurture and Income.  Let's do so again.

The graph below is from What Happens When We Randomly Assign Children to Families?, by Bruce Sacerdote
Holt's International Children's Services places children, primarily
Koreans, with families in the United States.  Holt has an interesting
proviso to their adoption contract, conditional on being accepted into
the program, children are randomly assigned.  Sacerdote has collected
data from children who were adopted between 1970-1980, and thus who
today are in their mid 20's or 30's, and their adoptive parents.

The graph shows how parent income at the time of adoption relates to
child income for the adopted and "biological" (non-adopted) children. 
The income of biological children increases strongly with parental
income but the income of adoptive children is flat in parent income. 
What does this mean?


The graph does not say that adopted children necessarily have low
income.  On the contrary, some have high and some have low income and
the same is true of biological children.  What the graph says is that
higher parental income predicts higher child income but only for
biological children and not for adoptees.

Now what about education?  Sacerdote looks at that as well.  He doesn't have a child SAT-score, parent-income correlation but he does find:

Having a college educated mother increases an adoptee's probability of
graduating from college by 7 percentage points, but raises a biological
child's probability of graduating from college by 26 percentage points.

The effect for father's years of education is even larger; about a ten times larger effect on biological children than on adoptees.  Similarly, parent income has a negligible effect, small and not statistically significant, on an adoptee completing college but an 8 times larger and statistically significant effect on a biological child completing college (Table 4, column 3). 


Very interesting, but hardly conclusive as we, at least from your post, do not know, at what age the children were adopted.
If the impact of care in early childhood is at all important in later life to sort out this issue we would need a random adoption study of children that were adopted immediately post birth.
But even that may not be fully conclusive, because the prebirth environment may affect later life outcomes, we would somehow need to control for things like prebirth nutrition, mother's stress level, etc.

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Pawel, adoption is in infancy and Sacerdote shows "that the child's weight in infancy and other pre-adoption characteristics are uncorrelated with adoptive parent characteristics such as family income, parental education etc."

Michael, I discussed this in my original post where I wrote "Some might suggest that parents treat their biological and adopted children differently and this is what accounts for the difference in incomes. The interpretation is very uncharitable to the parents who have volunteered to raise an adopted child and I think it implausible. Moreover, unless every adopted child is treated equally poorly in all families, then we would still expect the income of adoptees to increase with parental income but perhaps starting at a lower level."

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This begs another question. Are K-12 schools that better off parents send their kids to actually higher in quality on average, or are the higher recorded SAT scores of "better" schools the result of genes of their biological parents who presumably are wealthier due to better genes themselves? Note that a majority of parents try to send their kids to the best schools that they can reasonably afford, and this is usually done by buying a home in a more expensive suburb.

I'd love to see if the high schools these adopted kids went to had higher class SAT scores when the parents had higher income. If adoptees of better off parents almost always send their kids to K-12 school systems with better SAT score averages, then this study has very different implications than if those same parents in aggregate managed to send their kids to schools with a wide variety of different SAT averages.

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I took a look at the racial variation in SAT scores. I had data from '89 to '04, and average SAT scores for AAs, whites, and Asians. Assigning the CW mean IQ scores for the races (85, 100, and 105, respectively), r^2 was 0.93.

IQ is the determinant. The decline in SAT scores over the years is due to expandidng the test to lower IQ cohorts, as college attendance has expanded.

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Wow, this chart really undermines the libertarian/conservative presumption that good morals, hard work, the right upbringing, "merit", etc. are what leads to higher incomes.

It appears to be largely based on a genetic lottery with little or no role for parenting, neighborhood, etc. (at least not those components that are correlated with income).

If that's true, it provides a very interesting perspective on income inequality and social justice.

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Moreover, unless every adopted child is treated equally poorly in all families, then we would still expect the income of adoptees to increase with parental income but perhaps starting at a lower level.

Not necessarily. Some parents might treat their adoptees better than others; if that better treatment is uncorrelated with parental income, then you'd still see a flat adoptee income curve.

You're right that "parents treat adoptees worse than biological children" is an uncharitable explanation, but I don't see any data in this post to rule it out. Plus, it's certainly an intuitive explanation from a "selfish gene" point of view.

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The flatness of the graph cannot be explained by supposing that adoptees get treated worse than natural born children.

You would have to suppose that the discrepancy is greater among rich parents than poor parents, which is unlikely.

The graph proves zero effect of parental wealth, that inheritance of wealth is wholly through genes.

However, other graphs in the same paper hint at very great parental influence, uncorrelated with parental wealth. The income of adoptees tends to resemble the income of their adoptive siblings, but not their adoptive parents - which could be parents inculcating thrift and ambition, could be the inspiring example of adoptive siblings, could be the inspiring example of peer groups.

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Krugman and Yglesias err in using college enrollment as their ultimate outcome for intelligence. Union jobs and skilled trades can be a better option than college for many young people and are more encouraged by working class parents.

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Why is "IQ" treated as something independent of income?

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An earlier comment raises a good question. Does Sacerdote control for family size and birth order? Higher birth order (meaning, more siblings) has been shown to reduce labor market outcomes, mostly likely due to crowding out of parental resources (see Joseph Price's 2006/2007 JHR, Sandra Black's QJE paper, and Stephane Mechoulan's papers, all on birth order).

Adoption may also be more likely to occur as parents are older. What is the average age of the parents of the non-adoptees vs. the adoptees? Or is it that the pre-adoption characteristics of parents are balanced across treatment and control?

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adoptee kids got bad genes.

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Suprised no one has mentioned physical appearance as another inherited trait that might have a significant influence on income. File under "life's not fair", but I think it's still real. Hard to measure, of course, but we all can see it.

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The graph disproves nature, unless the Korean people (or all those adopted) as a gene pool are more inferior than nearly all Americans.

If the adoptees came in at $60K across the board, then outcomes would argue for genes determining outcomes because the high/low outcomes genes would be spread across adopting parent incomes and the outcomes would be near the median of the non-adoptive kids.

Nurture is a real possibility; guessing adoption in early years from poor economic status, nutrition would be less which would result in poorer performance as we see in the US, but long term in the US probably means good health (the advantage of being starved for longevity).

The more probably factor, in my view, but who knows I'm guessing, is the adoptees "differentness" negates the network effect benefits wealthier parents have and transfer to their kids. The kid of in Irish family cohort of the Kennedy clan would move easily in their Boston social scene, while the Korean kid would instant standout and cause people to pause and pull back, I'm guessing. So, while Teddy might instantly hug as he did everyone, others wouldn't quite rush in without thought, and that would transmit a certain caution to the kid so he pulls back and doesn't assume the favor would be granted and thus doesn't ask for the favor that certainly would be granted. So, the opportunity that exists isn't exploited.

However appearance is genetic, so for the latter to be true, genetics determines the outcome, but not skill, IQ, etc. But hey, we know those with the handsome/beauty genes get better jobs and have higher incomes.

Instead of education, maybe plastic surgery is needed to improve the outcomes of the chronically poor segments of society.

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As an infant adoptee, I've been thinking a little about the pros and cons of being adopted. Mostly, you just hear from dissatisfied adoptees who go on long disruptive searches for their biological parents. You don't hear much from satisfied adoptees like myself since our stories are so undramatic.

Certainly, I lacked for nothing in terms of love, care, and investment by my adoptive parents.

The differences of being adopted versus not being adopted are a little more subtle. I think an advantage of being adopted is that your parents are less likely to share your natural weaknesses. For example, I'm naturally procrastinatory and disorganized, but my adoptive parents were punctual and organized, so my childhood went smoothly. In contrast, two generations of genetically procrastinatory and disorganized blood relatives in the same house makes for some degree of chaos.

On the other hand, the lack of genetic links can hurt in getting nepotistic breaks in your career. My adoptive father was an engineer from a family of engineers, so he had lots of contacts in the engineering field he could have called upon to get me a start on an engineering career. But I have no engineering talent, and he wasn't related to and didn't know anybody who had the kind of talents I had. So, that's a downside.

All in all,

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A commenter asserts:

"The graph disproves nature, unless the Korean people (or all those adopted) as a gene pool are more inferior than nearly all Americans."

No, the reason the adoptees' average incomes are lower than their parents' average incomes is mostly because they are younger at the point of measurement. Couples generally don't give up trying to have their own children and decide to adopt until they are in their prime earning years. For example, my father was 42 when I was adopted.

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I never understood the point of these studies. Random researcher chooses a random metric for dividing a group of people and then proceeds to study various correlations based on that metric. Why study income, why not study eye color and how that is correlated with IQ and income and a whole bunch of other stuff. You could just as well post some nonsensical correlations related to eye color and claim they were significant.

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# Steve Sailer : Thanks for the personal story.

The "Nature, Nature..." almost seems a Freudian slip.

In all these discussions there almost always seems a clear ideological split : Libertarians& Conservatives favoring Nature and Liberals favoring Nurture.

An IQ Gene!! I'll try and explain that to my Dad who didn't finish 10th Grade in a less developed country but ensured I could see how much he valued education : because of that along the way I picked up a couple of Master's degrees and a stint at at an Ivy League university .

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Mankiw responds:

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@GaryD: Obviously you are missing whatever chromosome the "don't type in all caps" gene is on.

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This interpretation does not control for race and racial discrimination.

In fact, the graph shows that the mean income of all (mostly Korean) adoptees in the sample is much lower than the mean income of all (mostly white) non-adoptees. It even looks like it's at the tail end of the (mostly white) non-adoptee income distribution.

(Note that studies which show supposed higher Asian American income measure family income, not personal income, and non-adopted Asian American families tend have more family members than non-adopted White American families.)

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From Sacerdote's paper:

"The survey measure of family income is much higher for the non-adoptees than for the adoptees: $61,000 per year versus $42,000 per year. But this huge difference narrows to $1,600 when I control for age, education, and gender."

The adoptees' siblings who are biological children of the adopting parents are six years older on average and are about twice as likely to be male. The siblings are also more educated than the national average. (The adoption service assigns children randomly, except it will let you pick a child of the opposite sex if you only have children of one sex. 61% of the non-adopted children in the study are male versus only 30% of the adoptees. My guess is that a high proportion of adopting mother in this study are highly feminine and maternal women who love being moms, but have been blessed only with sons. Wanting a girly daughter to share their domestic joys with, they turn to Korean adoptions. But that's just a guess on motivation.)

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One change over my lifetime is that it's become more unusual for children to be adopted by families lower down the social ladder than their biological parents. My adoptive parents were solidly middle class, but my biological parents were more upper middle class. That's become rarer over the last half century.

On the other hand, egg donors increasingly come from the top ranks of society, with egg implantation doctors advertising for paid donors at Ivy League universities.

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Turpentine asks:

"So why are the results of the Sacerdote study so different than the ones from the study in Nature [Caprom & Duyme] posted on De Long's website? Anything that could explain it?"

I wrote about De Long's favorite nature-nurture study in my review of Nisbett's "Intelligence and How to Get It":

Nisbett is impressed by a 1989 study by two psychologists Christiane Capron and Michael Duyme. They attempted to overcome the usual “restriction of range† problem with adoption studies (agencies don’t let people who are likely to be lousy parents adopt children) by spending years searching for 40 adoptees whose biological parents were from the top 15 percent or bottom 15 percent of French society and had been adopted by parents at the top or bottom. They only found eight highborn adoptees who had followed the Oliver Twist path in being brought up in poverty, but they managed to fill out their other three cells for a sample size of 38. (Assessment of effects of socio-economic status on IQ in a full cross-fostering Nature, August 17, 1989.) On average, those children lucky enough to be placed among the rich averaged 12-point higher IQ scores at age 14 than those placed among the poor. That’s a bigger nurture effect than typically seen in American adoption studies, but it sounds plausible to me. (Note, however, it’s not clear that this IQ boost extended past puberty. It appears that, while children can be molded to some extent, adults tend to choose their own environments, with levels of intellectual stimulation best suited for their genetic endowments.)

And consider the cost to reproduce the benefits of having wealthy parents for millions of poor children. It’s not just the additional out-of-pocket expenditures, but the tens of thousands of hours of time spent by well-educated people talking individually to their children: likely seven-figures per child.

And yet, in this most pro-nurture of all the many adoption and twin studies yet done, the nature effect was still larger than the nurture effect. Highborn children averaged 16 points higher in IQ than lowborn children compared to the 12-point advantage seen among those raised rich.

Therefore, assuming this tiny study is correct, society could eliminate roughly 75 percent of the IQ gaps caused by genetic differences. All it would take is for the government to make parents in the upper and lower sectors of society exchange their children.

It would be like Mark Twain’s The Prince and the Pauper — as rewritten by Pol Pot.

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As for the flatness, you can Google "The Glass Ceiling and Asian Americans". Since there is a ceiling effect for Asian Americans in general, it is possible that there is a ceiling effect for Asian American adoptees as well.

You cannot assume that the impact of racial discrimination is constant across different income levels. It is possible that racial discrimination works by keeping a racial minority at the bottom or lower half of the social ladder. Racial minorities who take lower-income jobs may be less affected by racism, because their coworkers are more likely to be racial minorities as well. In contrast, upper management positions tend to become increasingly white.

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I suspect that the DeLong analysis ignores the fact that the non-IQ factors of physical beauty and temperament that affect income and academic achievement are also determined mostly by genetics.

The fact that genetics plays such a large role doesn't mean we shouldn't do all we reasonably can to ameliorate negative environmental factors.

Although temperament is mostly bred into rather than trained into dogs, raising a dog badly can ruin one that has a good genotype, while raising and training one well can to some degree counteract the negative tendencies of a breed.

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I'm not going to shell out $5 for the full article, but did anyone else notice that average incomes for biological children are 35k higher than their parents' if their parents earn 25k? That's more than a little weird.

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Using the kids' family income for this comparison seems messy messy messy, since it jumbles together the kids' earnings (conditional on employment) and spousal earnings (conditional on employment and marriage).

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One thing to keep in mind is that in nature-nurture disputes, it's easy to get into a pointless argument over whether the glass is half full or half empty.

Typically, adoption and twin studies show that the heritability of most traits is somewhere vaguely around 0.5. So, the nature glass is usually half full, as is the nurture glass. Simultaneously, they are both half empty.

On the other hand, much of the time we have no clue what composes the half-full nurture glass. Over the last 45 years, an enormous amount of money has been spent on studying ways to improve nurture to close gaps, from the Coleman Report on down, with much less success than was anticipated back during the Great Society.

I've been following the social science literature since 1972 (my first published letter to the editor in National Review was a comment on sociologist Christopher Jencks' re-assessment of the Coleman report when I was a freshman in high school). Not much has changed in the social science results since 1972.

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I'm a Korean Holt adoptee and some of the comments are quite funny to me. My parents love me as much as they would any biological child. I think that we'd like to think that nurture plays are larger role in what happens, but I do believe what the article is trying to say. I was adopted into a lower income family and I have an MBA from a great school and am currently in med school. My income has been and will be quite a bit larger than my family's - it works both ways. They did a great job raising me, but I didn't have all "advantages" (whatever they may be) by being raised in a more affluent family. Neither of my parents completed college, so they couldn't help me navigate the application process or how to acclimate.

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I am surprised at how uncritical most are of the data. Without having seen the original, and admittedly having no real interest in pursuing the details, my reaction on seeing these graphs for a second time is that the data provide no basis for any meaningful conclusion. When I first read the results my reaction was that the idea sounded plausible, but on a second viewing there does not seem to be anything of value. The non-adopted results do not look to provide any evidence of a wealth effect other than for the lowest category. After that the results bounce so much that all the variation appears to be within the range of error, thus income for children at all points other than the lowest is not correlated with income of parents and appears to be spread around the population mean. The income for adopted children is flat as well, but lower at all points. This suggest to me that the explanation given in the original post simply does not hold. Given that Alex's point in the original post was mine prior to reading his post, I have changed my mind. Once again I am back to having no clear point of view on the issue. As we have one biological and one adopted child, it would be helpful to have some convincing information on the subject, but this is clearly not sufficient.

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The link to the free paper posted by Steve Sailer above is wrong; here's one that works:

It would be nice if people read the paper before commenting, but that's probably too much to ask.

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"I was adopted into a lower income family and I have an MBA from a great school and am currently in med school."

To me, this says the education establishment needs to get their act together before we go any further. They really are shite at recognizing talent.

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Parents income at the time of adoption? Hmmm. A number of college educated couples will have low income at the time of adoption and higher income during the child's gradeschool and highschool development. I wish the axis were average adult income over the child's school years.

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What's weird about that chart is the flatness of the adoptee's income. It makes sense that (if the pool is big enough) the average IQ of a random batch of adoptees would be 100--the set average. And so it makes sense--because income and IQ corellate strongly--that that batch of adoptees would earn the average american income, which is about 40K. What doesn't make sense is that family wealth would have no impact at all. Do we really live in such a perfect meritocracy?

Another thing that Steve Sailer mentioned: When controlled for age and gender the difference in incomes between adoptees and non-adoptees narrows to $1600. Doesn't that make the chart we are all so interested moot? What am I not understanding?

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it's clear from the graph that there is an adopted child gene.

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"lib = belief in evolution"
-- Andrew at Aug 29, 2009 5:29:27 PM

What the.....?

Contrapositive: not-lib = dis-belief in evolution.

Therefore: Andrew = empty noggin?

What if you're neither lib or not-lib [conservative?]?

Get real, dude!

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International adoptions are extremely complicated and the health risks associated well-known among real experts on the issue. After reviewing nearly 1,000 cases of international adoption Dr. Dana Johnson has stated
"The chance of an institutionalized child being completely normal is essentially zero".

Expert opinion on this can be easily found on the Internet this avoiding the opinions of economists dabbling in fields outside their area of expertise.

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Forgive me if I am not looking at it right (sometimes I am not good with numbers) but it seems like the post by mulp may be incorrectly assuming that the mean non-adoptee income is up near $60 000, when in fact it could be near $41, 000, close to the mean of the adoptees (as Alex said the graph doesn't show non- adoptees necessarily earn more than adoptees). I trust the nice readers at MR will kindly correct me if I am the one making the error, and perhaps they may also be familiar with the original study to come up with the empirical mean for the adoptee and parent incomes.

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A most inconclusive graph, unless we know the age at which the kids were adopted.
The importance of early mental training cannot be over-emphasised. Old habits die hard. Bad learning habits imbibed at an early age are difficult to correct. Also, there is the issue of differential treatment that may be meted out to adopted children. I suspect parents are unlikely to give the same degree of attention and care to adopted kids as they would to one of their own

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great post, thanks!

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Ben, what the hell are you babbling about? And where in any of this discussion did "people of African descent" get mentioned?

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"I suggest you read Stephen Jay Gould's Mismeasure of Man"

The book got panned in a number of academic journals, here are some of the criticisms:

1. Gould's allegation that Morton had doctored his skull collection was re-investigated by John Michael. Michael found very few errors & those that were found were not in the direction Gould claimed. Michael found Gould was mistaken & that Morton's studies were conducted with integrity. Michael JS 1988. A new look at Morton's craniological research. Current Anthropology 29: 349- 54.

Gould didn't mention this in the 1996 edition of his book.

2. Gould's central argument against hereditarians happens to be based on his gross misunderstanding of the position he is criticizing. He says, "a reified Spearman's g is still the only promising justification for hereditarian theories of mean differences in IQ among human groups .... The chimerical nature of g is the rotten core of Jensen's edifice, and of the entire hereditarian school." (Gould 1981, 320) In reality, Jensen's views on the genetic explanation of racial differences in IQ are totally independent from the question whether there is only one factor of general intelligence (so-called g). Here is what James Flynn, a consistent critic of Jensen, has to say on the matter:

"Gould's book evades all of Jensen's best arguments for a genetic component in the black-white IQ gap, by positing that they are dependent on the concept of g as a general intelligence factor. Therefore, Gould believes that if he can discredit g, no more need be said. This is manifestly false. Jensen's arguments would bite no matter whether blacks suffered from a score deficit on one or 10 or 100 factors. I attribute no intent or motive to Gould, it is just that you cannot rebut arguments if you do not acknowledge and address them."

3. Gould criticises the idea that brain volume could be related to cognitive ability, but ignored a literature review by Van Valen (1974) which estimated an overall correlation of 0.30 between brain size and intelligence. With MRI scans this evidence continued to accumulate through the 80's.

Rather than address this evidence, Gould's 1996 edition simply deletes the section of the 1981 dition that discussed the brain-size/IQ relation.

Recently Richard Haier, at Brain Research Institute, UC Irvine College of Medicine, found that general human intelligence appears to be correlated with the volume and location of gray matter tissue in the brain.

For a summary of the neurobiological correlates with 'g' see this summary by UCLA neuroscientist Paul Thompson

Also, see this article in New Scientist dated 11 March 2009, discussing the recent twin studies on myelination & intelligence:

" By comparing brain maps of identical twins, which share the same genes, with fraternal twins, which share about half their genes, the team calculate that myelin integrity is genetically determined in many brain areas important for intelligence. This includes the corpus callosum, which integrates signals from the left and right sides of the body, and the parietal lobes, responsible for visual and spatial reasoning and logic (see above). Myelin quality in these areas was also correlated with scores on tests of abstract reasoning and overall intelligence (The Journal of Neuroscience, vol 29, p 2212).

Just because intelligence is strongly genetic, that doesn't mean it cannot be improved. "It's just the opposite," says Richard Haier, of the University of California, Irvine, who works with Thompson. "If it's genetic, it's biochemical, and we have all kinds of ways of influencing biochemistry."

4. Gould's criticism of factor analysis (and 'g') is flawed: see John Carroll's review Intelligence 21, 121-134 1995 and also Jensen Contemporary Education Review Summer 1982, Volume 1, Number 2, pp. 121- 135.

David J. Bartholomew, from London School of Economics, who has written a textbook on factor analysis, also explains in "Measuring Intelligence: Facts and Fallacies" explains where Gould goes wrong in this area.

5. Gould suggests that Jews tested poorly in the 1920's & this lead to the Immigration Act 1924. Both are incorrect.

6. The idea that Jews tested poorly is actually based on a misrepresentation of a paper authored by Henry Goddard in 1917. Goddard gave IQ tests to people suspected of being mentally handicapped. He found the tests identified a number of such people from various immigrant groups, including Ashkenazi Jews. Leon Kamin in 1974 reported that Goddard had found Jews had low IQ scores. However, Goddard never found that Jews or other groups as a general population had low scores. There is other information that contradicts the idea that Jews did poorly on IQ tests around this time. In 1900, in London, Jews took a disproportionate number of academic prizes in spite of their poverty (C Russell & H.S. Lewis 'The Jew in London' Harper Collins 1900). Also, note that by 1922 Jewish students made up more than a fifth of Harvard undergraduates & the Ivy League was already instituting policies aimed at limiting Jewish admissions (the infamous 'Jewish quotas'). Also, a 1920's a survey of IQ scores in three London schools with mixed Jewish & non-Jewish student bodies - one prosperous, one poor and one very poor - showed that Jewish students, on average, had higher IQ's than their schoolmates in each of the groups (A Hughes 1928).

- see also: G. Cochran, J. Hardy, H. Harpending, Natural History of Ashkenazi Intelligence, Journal of Biosocial Science 38 (5), pp. 659-693 (2006).

7. The other misconception is that this contributed to the 1924 Immigration Act. However, Herrnstein & Snyderman found this was not the case (Intelligence Tests and the Immigration Act of 1924' American Psychologist 38, September 1983).

8. Although it was claimed Cyril Burt made up data for his twin studies, subsequent investigations have cast doubt on this. See the book Cyril Burt 'Fraud or Framed', edited by Nick Mackintosh former Chair of Psychology at the University of Cambridge.

9. In the first edition Gould noted that "the only really natural experiment for separating genetic from environmental effects in humans [is] genetically identical individuals raised in disparate environments. Studies of identical twins raised apart should therefore hold pride of place in literature on inheritance of IQ.† Gould repeated that statement verbatim (page 264) in the 1996 reissue. He completely ignored the fact that by far the most extensive and careful study of identical twins raised apart from infancy in different families in different social environments had been begun in 1979 and its results were widely reported well before 1996. The only reason that Gould could have had for ignoring the Minnesota Twin Study is that he could not refute its results and he knew he could rely on the ignorance of reviewers in the popular press.

Steven Pinker commented on the results of twin studies in the NY Times earlier this year:

"To study something scientifically, you first have to measure it, and psychologists have developed tests for many mental traits. And contrary to popular opinion, the tests work pretty well: they give a similar measurement of a person every time they are administered, and they statistically predict life outcomes like school and job performance, psychiatric diagnoses and marital stability. Tests for intelligence might ask people to recite a string of digits backward, define a word like "predicament," identify what an egg and a seed have in common or assemble four triangles into a square.

The most prominent finding of behavioral genetics has been summarized by the psychologist Eric Turkheimer: "The nature-nurture debate is over. . . . All human behavioral traits are heritable." By this he meant that a substantial fraction of the variation among individuals within a culture can be linked to variation in their genes. Whether you measure intelligence or personality, religiosity or political orientation, television watching or cigarette smoking, the outcome is the same. Identical twins (who share all their genes) are more similar than fraternal twins (who share half their genes that vary among people). Biological siblings (who share half those genes too) are more similar than adopted siblings (who share no more genes than do strangers). And identical twins separated at birth and raised in different adoptive homes (who share their genes but not their environments) are uncannily similar."

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PS. You can also find the article on my site at the link just above.

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I don't know if anyone has done stuff about income but I do know that its very strongly correlated to height.

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of course if you weren't just trying to make a sniping and infantile partisan point you could have also said, 'i guess this completely knocks down the liberal myth that throwing more money at a problem helps to alleviate it' - hidik

Um, excuse me, but it's a CONSERVATIVE myth that liberals believe "throwing more money at a problem helps to alleviate it". (Speaking of making a "sniping and infantile partisan point"!)


adoptee kids got bad genes - jz

This is obviously a gross overstatement (What kinda genes you got, jz?).

However, I can see how it might be reasonably argued that biological parents of adoptee children display poor impulse control (to wit, the impulsive decision to have---usually unprotected---sex, without intending a pregnancy!), and to wonder whether that trait is heritable. [Poor impulse control being a likely source of lower income?]

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The idea that success is entirely due to genetics is retarded. End of story.

The idea is completely implausible. Are we supposed to believe that it does not matter whether a child is raised by alcoholics and crack addicts or broken homes?

Are we supposed to believe that when the wealthy consume expensive tutoring, college consultants, and private education for their children, that they are acting stupidly, because all that matters is genetics anyway?

Are we to believe that school environments where there is a lot of disruption and gang-influence don't hinder performance?


There is a very HEAVY burden on those like Alex Tabarrok and Greg Mankiw who want to advance the implausible stories. They are just to extreme.

What are Brad DeLong and Matt Yglesias and Paul Krugman arguing? Simply this. Genetics is not the ONLY THING that matters. Genetics matters, but so does environment. What is the argument that Greg Mankiw and Alex Tabarrok making. Genetics is ALL that matters or the thing that PRIMARILY matters.

In other words, Mankiw and Tabarrok are arguing for a very extreme position that conflicts with common sense. Delong, Yglesias and Krugman are taking much more sensible moderate positions.

In light of that. I don't find the idea that parents are more generous to their own biological children than adopted children implausible. I also don't find the idea that Korean children tend to face discrimination and cultural alienation (something that would tend to harm their income potential regardless of the income of their adoptive parents) implausible.

In fact, I definitely find these explanations of the data a lot less implausible than the extremist idea that environment does not matter for success at all or very little.

Overall, I think it is fair to say that Alex Tabarrok is a very smart idiot. And contrary to Tyler Cowen's substanceless remark to the contrary, his post is FAR inferior to those by Krugman, DeLong, and Yglesias on this matter.

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