Saturday, December 06, 2008

Nature vs Nurture: A Natural Experiment

I have been engaged in a long Usenet thread (much of it here) coming out of my claim that hostility to evolution isn't limited to the religious right, that the left, although unwilling to reject the theory of evolution, is also unwilling to accept implications of evolutionary biology that are politically incorrect. The main thing I've gotten out of the thread is evidence supporting that claim—although, of course, those who provided that evidence may disagree.

But recently someone pointed out an interesting paper which provides evidence on a related question of considerable interest: To what extent are outcomes for a child determined by the environment he is raised in, to what extent by his genes? Children of well off and well educated parents tend to end up richer and better educated than children of parents with the opposite characteristics. Is that because of a superior environment or superior genes?

From 1970-1980, a large number of Korean-American children were placed for adoption by an agency which assigned them at random to adoptive families. That meant that any correlation between characteristics of the families, such as maternal education, socio-economic status, or income, and characteristics of the children as adults, would be due to environment not genetics. By comparing the strength of the relation between characteristics of parents and adoptive children with the corresponding figure for parents and biological children raised by those parents, one can get at least some estimate of how much of the relation comes from which cause.

The conclusion is striking. An increase of one year in maternal education produces an increase of only .07 years in the education of an adoptive child but an effect four times as large on the education of a biological child. Similar results apply to a variety of other characteristics. It looks as though being brought up by well off or well education parents is indeed an advantage, but a considerably smaller advantage than being the biological child of such parents.

One important qualification to that result is to note that all of the adoptive families had to be certified by the adoption agency as suitable to adopt. That would presumably cut off some of the lower tail of the distribution—an alcoholic unmarried mother would be unlikely to qualify. And, they had to be families that wanted to adopt, which again would eliminate some. But at least over the range of environments in the sample, nurture seems to be a good deal less important than nature.

The study, as so far described, is limited to particular, readily measured, characteristics of the adoptive parents. Having a well educated adoptive mother doesn't have much effect on how much education you get. But having an adoptive mother who cares a lot about her children and pays them a lot of attention might.

To test that possibility the author of the paper looked at the relation between characteristics of siblings. Adoptive siblings, like biological siblings, are brought up in the same household, but, unlike biological siblings, are not genetically related. So if some households are much better places to be brought up in than others, one would expect the result to show up in the relation between (say) years of education of adoptive siblings.

There is such a relation, but it is only a little stronger, relative to the corresponding relation between biological siblings, than in the parent/child case. An extra year of education by an adoptive sibling predicts, on average, an extra .09 years of education, for a biological sibling an extra .29. The effect is stronger for income: .16 vs .29.

A further limitation in the study is that it does not distinguish a relation between biological parent and child or biological siblings due to shared genetics from one due to pre-natal environment. Arguably, better educated and higher income mothers are in better condition during pregnancy, which could result in better children for (pre-natal) environmental reasons rather than genetic reasons. That does not affect the absolute level of the effect for adoptive children but might make the genetic contribution to the difference between adoptive and biological look larger than it really is.

24 Comments:

At 12:04 PM, December 06, 2008, Anonymous RKN said...

From 1970-1980, a large number of Korean-American children were placed for adoption by an agency which assigned them at random to adoptive families. That meant that any correlation between characteristics of the families, such as maternal education, socio-economic status, or income, and characteristics of the children as adults, would be due to environment not genetics.

I don't think so, unless the children were isogenic.

 
At 1:40 PM, December 06, 2008, Blogger Michael F. Martin said...

I myself am a natural experiment in the nature against nurture debate. My paternal twin and I were adopted into the same family along with a sister who is not biologically related. My brother and I both finished college, although only I went on to complete graduate school degrees (two). My sister dropped out of high school, but later completed her GED and an Associates degree at a local junior college. My adoptive parents both have graduate school degrees.

But it's not a perfect experiment because (aside from the small sample size), I have met my biological parents, and both also have graduate degrees. In fact, both my biological and adoptive father are lawyers as I am. If anything, I have the most in common with my adoptive father, who is also a patent lawyer.

So maybe you need the genes and the upbringing, but not necessarily from somebody with the same genes?

 
At 3:01 PM, December 06, 2008, Anonymous Anonymous said...

My senior thesis was on Nature vs Nurture and was based on identical twins who were separated at birth. The similarities between the two were unreal. One case I remember particularly well was of twins who married women with the same first name, name their sons' the same (with different spellings), had the same type of dog and even drove the same model of car. I will I had all my notes so I could quote my references but the research was done in 1987. I am sure there is plenty to found on the internet.

 
At 4:20 PM, December 06, 2008, Blogger Jacob said...

There's another reason why left-leaning people sometimes are reluctant to talk about Darwinism: implications of there being a genetic elite.


Darwinism receives a lot of criticism because it is an unfinished theory. There simply must be more things going on than random mutation to change the genes. The theory of evolutionary developmentalism, supports the thought that genes can be changed during an organism's life time, and that that change later be passed on to the organism's offspring. In my mind, there would be no other way of explaining an organism's instincts, it knowing how to do things without ever being taught how to do them, unless this theory were true.


How does a sheep dog know to herd sheep or other animals from the moment it is born? When its ancestors were herding sheep, the behavior must have been imprinted on their genes and passed on to their offspring. There's no other explanation as far as I'm concerned. Behavior changes the genes and the behavior of the offspring.

 
At 6:02 PM, December 06, 2008, Anonymous Rex Little said...

I'm involved in an ongoing nature vs. nurture experiment, which is coming down hard on the side of nature. My stepson's biological father is a high school dropout, alcoholic and drug addict. He had visitation with his son the whole time he was growing up, but did not have custody from the time the boy was about 1. I married the boy's mom when he was 5, and we've raised him together since then. I'm a college graduate, and I don't drink, smoke or use drugs.

The boy (now 22) has a drug habit and a smoking habit, can't keep a job, and has been arrested several times for offenses both drug-related and not. He is in jail as I write this.

The alcoholic father has another son whom he raised (mostly by himself) but who was adopted and therefore is not genetically related. (I don't know a whole lot about his birth parents, but they aren't addicts or criminals.) This son is a good, clean-living guy with a steady job, a wife and two kids.

 
At 7:23 AM, December 07, 2008, Blogger Nate said...

Of course, to be anti-PC in the other direction...parents could be much less nurturing towards adoptive kids than genetically related kids which might explain the lack of educational advantage. Or, the fact that you are a Korean-American in our society might put you in Asian-American peer groups which tend to value and reward school success more often than the norm.

 
At 8:41 AM, December 07, 2008, Blogger David Friedman said...

"Of course, to be anti-PC in the other direction...parents could be much less nurturing towards adoptive kids than genetically related kids which might explain the lack of educational advantage."

The comparison isn't between number of years of education of adopted children and of biological children but of the effect of mother's education on adopted children vs the effect of mother's education on biological children. So your argument requires not that parents treat adopted children less well but that the effect of characteristics of the parent on how parents treat children is less for adopted children.

 
At 10:41 AM, December 07, 2008, Blogger Joe said...

When we talk about nature vs. nurture, I think it's also important to factor in the environmental factors of the pre-natal environment. Perhaps things like the mother's diet and consumption, emotions, and types of activity play a large part in the outcome of the child. We shouldn't forget that there is a lot of very significant nurturing that a child goes through before it is put up for adoption. I tend to agree with you that nature is very important, but if we don't isolate the effects of these factors, it could cause us to overemphasize the nature side.

 
At 7:23 PM, December 07, 2008, Blogger chriscal12 said...

This comment has been removed by the author.

 
At 7:27 PM, December 07, 2008, Blogger chriscal12 said...

On a slight tangent, I wonder if you are aware of the current controversy that Walter Block is involved in.
He recently made some statements at Loyola College in Maryland along the exact lines of your argument in the linked Usenet debate. That men have a wider distribution of abilities, high and low, and that women tend toward the mean. He has written a few articles on LewRockwell.com about the incident, and has challenged anyone willing to a public debate on the subject (so far no takers).

His first article on this episode can be found here, and he has several others here.

Just thought this might be of interest to you.

 
At 3:05 AM, December 08, 2008, Blogger Mike Huben said...

I notice that the authors do not bring up nature/nurture in the abstract. I doubt that they would bring up anything as stupid as that in the paper.

Unless the adopted children were placed into Korean families, it would be screamingly obvious that they were adopted. Children labeled as adopted face a different social environment than biological children. Because this factor is variable, you can't really say anything about nature versus nurture from this experiment except for a few factors that are already known to be due to genetically derived physiology, such as height.

 
At 11:31 AM, December 08, 2008, Blogger Robin said...

I'm not sure if I'd describe people on the left as hostile to the idea of evolution, they're just opposed to some of its more speculative conclusions.

People on the right believe in creationism, an idea with no scientific merit. People on the left believe that cultural differences can be used to explain differences between the sexes and races and that genetics plays little or no role in intelligence. An idea which is defensible without resorting to silly religious dogma.

I am skeptic of the influence of genetics on intelligence (as well as the idea that the IQ test is especially useful). Aside from the fact that we don't understand culture well enough or have enough data about it to control for it in an experiment, we also haven't distinguished intelligence from personality.

 
At 10:18 AM, December 09, 2008, Blogger Don said...

"People on the right believe in creationism"

I'm on the right; I don't believe in creationism. All my friends are conservatives; none of them believe in creationism. The Catholic Church has stated (many times) that good Catholics can accept evolution.

Creationism is not the belief that God (or gods) exist; it is a specific, though fluid, set of beliefs that include the untenable idea that the earth is 5000 years old (or whatever).

While you're patting yourself on the back for the left's supposed commitment to rational, as opposed to superstitious, thought, I invite you take a tour of modern university and gaze at the leftists in their natural environment. Economics? Feminist anthropology? Race studies?

Hell, mention that people even HAVE genes and you're likely to be called a racist.

 
At 10:23 AM, December 09, 2008, Blogger Don said...

Continuing my thought: I don't think THESE right wingers believe in creationism:

http://secularright.org/

Remind me again, what church did Barack Obama attend for 20 years? Oh yeah, the one where evolution is a Jewish plot to undermine God's work. I guess Obama's a right winger, too.

 
At 5:46 PM, December 09, 2008, Anonymous Anonymous said...

Anecdotes can be useful in a debate like this, but I'm a bit disturbed to see people on this blog drawing sweeping conclusions from their sample-of-one experiences.

 
At 11:18 AM, December 11, 2008, Anonymous Rex Little said...

I'm a bit disturbed to see people on this blog drawing sweeping conclusions from their sample-of-one experiences.

Who, exactly, do you see doing this? If you're referring to me, I did nothing of the sort; I only said that my particular experience weighs in on the side of heredity. It's just one data point (or two, if you count each son separately), and I fully realize that.

Looking at the other comments, I don't see anyone else generalizing from one experience, either.

 
At 5:22 PM, December 12, 2008, Anonymous bobw said...

I recall a study several years ago that compared the career success (probably scored by income, though I don't remember the details) of college graduates from highly-rated institutions with those from other institutions. However, instead of comparing, for example, graduates from institution "A" with the graduates from institution "B,", the study compared graduates from "A" with graduates from "B" who had been admitted to "A." The study indicated that there was a correlation with the institute attended, but that the effect diminished rapidly with time. The authors concluded that the benefit of attending a highly-ranked institution was primarily reflected in the first job obtained after graduation; after that, you're on your own.

 
At 6:33 PM, December 16, 2008, Anonymous Anonymous said...

On the other hand, this seems to be assuming that parents who give up a child for adoption are in some way 'inferior', which may or may not be the case.
Further, there is some evidence that suggests that if a mother is under severe stress, her child may have problems later on, so the cause could still be enviromental, although something that the adoptive parents may not be able to control. Along those lines, even people adopted as infants often spend the first months of their life in a sub-optimal enviroment, which may start them off at a disadvantage.
Finally, there is also strong evidence that many transracial adoptees (and I'd assume that the majority of these Korean adoptees were adopted by white parents)of often have emotional problems that might well impact their future success.
So, while genetics may be *a* factor, I think that there are too many variables involved to say if it is the only factor.

 
At 5:00 PM, January 02, 2009, Blogger Damien Sullivan said...

Good comment by that last Anonymous.

David:
To what extent are outcomes for a child determined by the environment he is raised in, to what extent by his genes?

The answer to that question is itself dependent upon the environment, as cautions regarding heritability studies point out. Ironically, a liberal environment like Sweden, providing optimal environments for everyone, will magnify the effects of genes (as there's little else left to vary), while a conservative (in the socially stratified sense) environment will tend to obscure genetics with environment, with people being short and stupid due to malnutrition due to hereditary lack of property or other factors.

As for science and politics: true, not all right-wingers are Creationists! But still, the political home of Creationism and denial of global warming, both involving defiance of broad scientific consensus with fairly simple explanations, is the right. Areas where the left and science might conflict include paranoia regarding nuclear power, gun control, economics, and yes genetic effects in human minds -- but I regard all of these as murkier cases, with ambiguous results or value-dependent assessments. Gun control studies are ambiguous, the practical expertise of the economic community is not as obvious or settled as in the natural sciences, human genomics has barely been scratched and the mind little-understood, despite much research.

Of course, then there's the real woo -- crystals and alternative medicine on the left, faith healing on the right, astrology everywhere but maybe biased to the left. (Again, 'on' meaning 'finds a accepted home in', not "all members of that wing believe in X").

Jacob: There simply must be more things going on than random mutation to change the genes

No, there is no such requirement. The Baldwin effect describes how learned behaviors can enter the genome, not through a neo-Lamarckian mechanism but through Darwinian selection of predisposition to learn such behaviors, until they are wired in. As for the more dramatic canine behaviors, my understanding is that they tend to be exaggerations of various parts of the wolf's hunting repertoire. In theory the Baldwin effect could work too, but breeding a 'wolf' that harassed 'prey' without biting them was probably much faster. Ditto for a 'wolf' that obviously attends to prey without chasing it (pointers) or chases down fallen prey (setters? I'm not up on my dog types.)

 
At 7:42 PM, January 26, 2009, Anonymous Ben said...

Interesting summary of adoption studies on Gene Expression, which seem to suggest nature is more important.

"Contrary to "culture" theory, the ethnic academic gaps are almost identical for transracially adopted children, and to the extent they are different they go in the opposite direction predicted by culture theory. The gap between whites and Asians fluctuated from 19 to .09 in the NAEP data while the gap in the adoption data is from 1/3 to 3 times larger. This is consistent with the Sue and Okazaki paper above which showed that contrary to popular anecdotes, the values that lead to higher academic grades are actually found more often in white homes. In other words Asian-Americans perform highly despite their Asian home cultural environment not because of it. And though the sample is meager, I find it interesting that the gap between the black and white adopted children was virtually identical (within just 4-6 points) to the gap between whites and blacks in the general population, just like in the Scarr adoption study.


[1] Clark, E. A., & Hanisee, J. (1982). Intellectual and adaptive
performance of Asian children in adoptive American settings.
Developmental Psychology, 18, 595–599.

Frydman, M., & Lynn, R. (1989). The intelligence of Korean children
adopted in Belgium. Personality and Individual Differences, 12, 1323–1325.

Winick, M., Meyer, K. K., & Harris, R. C. (1975). Malnutrition and
environmental enrichment by early adoption. Science, 190, 1173–1175."

http://www.gnxp.com/MT2/archives/004064.html

 
At 10:41 AM, February 20, 2009, Anonymous alcoholics said...

In indulgent in alcohol caused many parents to be departed from their siblings.
Being an alcohol dependent becomes an impediment in raising a child. Because alcoholism creates pattern of misbehavior, children may also developed the same habit as they grow up.

 
At 8:23 PM, November 10, 2009, Blogger Maya said...

Just curious...do you think that kids who's parents believe they have psychic abilities may be brought up to believe they do as well?

 
At 3:03 PM, November 23, 2009, Blogger TheVidra said...

JAcob, you wrote:
"There's another reason why left-leaning people sometimes are reluctant to talk about Darwinism: implications of there being a genetic elite."

Isn't that the whole basis of the left, i.e. that there is a genetic elite (whose role is to shepherd the masses, for their own good; noblesse oblige, so to speak)?

 
At 7:00 PM, November 25, 2009, Blogger Damien Sullivan said...

"Isn't that the whole basis of the left, i.e. that there is a genetic elite (whose role is to shepherd the masses, for their own good; noblesse oblige, so to speak)? "

Uh, no. Really no.

That's on the order of saying "isn't the whole basis of Christianity the worship of Zeus and Hera for salvation?" The misunderstanding is so profound that one doesn't know where to begin.

 

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