Red Flag of Twin Studies

Consider this a public service announcement. The moment someone turns to twin studies as reliable and meaningful evidence, it’s a dead give away about the kind of person they are. And when someone uses this research in the belief they are proving genetic causes, it demonstrates a number of things.

First and foremost, it shows they don’t understand what is heritability. It is about population level factors and can tell us nothing about individuals, much less disentangle genetics from epigenetics and environment. Heritability does not mean genetic inheritance, although even some scientists who know better sometimes talk as if they are the same thing. The fact of the matter is, beyond basic shared traits (e.g., two eyes, instead of one or three), there is little research proving direct genetic causation, typically only seen in a few rare diseases. All that heritability can do is point to the possibility of genetic causes, but all that allows is the articulation of a hypothesis to be tested by actual genetic research which is rarely done.

And second, this gives away the ideological game being played. Either the person ideologically identifies as a eugenicist, racist, etc or has unconsciously assimilated eugenicist, racist, etc ideology without realizing it. In either case, there is next to zero chance that any worthwhile discussion will follow from it. It doesn’t matter what is the individual’s motivations or if they are even aware of them. It’s probably best to just walk away. You don’t need to call them out, much less call them a racist or whatever. You know all that you need to know at that point. Just walk away. And if you don’t walk away, go into the situation with your eyes wide open for you are entering a battlefield of ideological rhetoric.

So, keep this in mind. Twin studies are some of the worst research around, opposite of how they get portrayed by ideologues as being strong evidence. Treat them as you would the low quality epidemiological research in nutrition studies (such as the disproven Seven Countries Study and China Study). They are evidence, at best, to be considered in a larger context of information but not to be taken alone as significant and meaningful. Besides, the twin studies are so poorly designed and so sparse in number that not much can be said about them. If anything, all they are evidence for is how to do science badly. That isn’t to say that, theoretically, twin studies couldn’t be designed well, but as far as I know it hasn’t happened yet. It’s not easy research to do for obvious reasons, as humans are complex creatures part of complex conditions.

For someone to even mention twin studies, other than to criticize them, is a red flag. Scrutinize carefully anything such a person says. Or better yet, when possible, simply ignore them. The problem with weak evidence that is repeated as if true is that it never really is about the evidence in the first place. Twin studies is one of those things that, like dog whistle politics, stands in for something else. It is what I call a symbolic conflation, a distraction tactic to point away from the real issue. Few people talking about twin studies actually care about either twins or science. You aren’t going to convince a believer that their beliefs are false. If anything, they will become even more vehement in their beliefs and you’ll end up frustrated.

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What Genetics Does And Doesn’t Tell Us
Heritability & Inheritance, Genetics & Epigenetics, Etc
Unseen Influences: Race, Gender, and Twins
Weak Evidence, Weak Argument: Race, IQ, Adoption
Identically Different: A Scientist Changes His Mind

Exploding the “Separated-at-Birth” Twin Study Myth
by Jay Joseph, PsyD

“The reader whose knowledge of separated twin studies comes only from the secondary accounts provided by textbooks can have little idea of what, in the eyes of the original investigators, constitutes a pair of ‘separated’ twins”—Evolutionary geneticist Richard Lewontin, neurobiologist Steven Rose, and psychologist Leon Kamin in Not in Our Genes, 19841

“The Myth of the Separated Identical Twins”—Chapter title in sociologist Howard Taylor’s The IQ Game, 19802

Supporters of the nature (genetic) side of the “nature versus nurture” debate often cite studies of “reared-apart” or “separated” MZ twin pairs (identical, monozygotic) in support of their positions.3 In this article I present evidence that, in fact, most studied pairs of this type do not qualify as reared-apart or separated twins.

Other than several single-case and small multiple-case reports that have appeared since the 1920s, there have been only six published “twins reared apart” (TRA) studies. (The IQ TRA study by British psychologist Cyril Burt was discredited in the late 1970s on suspicions of fraud, and is no longer part of the TRA study literature.) The authors of these six studies assessed twin resemblance and calculated correlations for “intelligence” (IQ), “personality,” and other aspects of human behavior. In the first three studies—by Horatio Newman and colleagues in 1937 (United States, 29 MZ pairs), James Shields in 1962 (Great Britain, 44 MZ pairs), and Niels Juel-Nielsen in 1965 (Denmark, 12 MZ pairs)—the authors provided over 500 pages of detailed case-history information for the combined 75 MZ pairs they studied.

The three subsequent TRA studies were published in the 1980s and 1990s, and included Thomas J. Bouchard, Jr. and colleagues’ widely cited “Minnesota Study of Twins Reared Apart” (MISTRA), and studies performed in Sweden and Finland. In the Swedish study, the researchers defined twin pairs as “reared apart” if they had been “separated by the age of 11.”4 In the Finnish study, the average age at separation was 4.3 years, and 12 of the 30 “reared-apart” MZ pairs were separated between the ages of 6 and 10.5 In contrast to the original three studies, the authors of these more recent studies did not provide case-history information for the pairs they investigated. (The MISTRA researchers did publish a few selected case histories, some of which, like the famous “Three Identical Strangers” triplets, had already been publicized in the media.)

The Newman et al. and Shields studies were based on twins who had volunteered to participate after responding to media or researcher appeals to do so in the interest of scientific research. As Leon Kamin and other analysts pointed out long ago, however, TRA studies based on volunteer twins are plagued by similarity biases, in part because twins had to have known of each other’s existence to be able to participate in the study. Like the famous MISTRA “Firefighter Pair,” some twins discovered each other because of their behavioral similarities. The MISTRA researchers arrived at their conclusions in favor of genetics on the basis of a similarity-biased volunteer twin sample. […]

Contrary to the common contemporary claim that twin pairs found in TRA studies were “separated at birth”—which should mean that twins did not know each other or interact with each other between their near-birth separation and the time they were reunited for the study—the information provided by the original researchers shows that few if any MZ pairs fit this description. This is even more obvious in the 1962 Shields study. As seen in the tables below and in the case descriptions:

  • Some pairs were separated well after birth
  • Some pairs grew up nearby to each other and attended school together
  • Most pairs grew up in similar cultural and socioeconomic environments
  • Many pairs were raised by different members of the same family
  • Most pairs had varying degrees of contact while growing up
  • Some pairs had a close relationship as adults
  • Some pairs were reunited and lived together for periods of time

In other words, in addition to sharing a common prenatal environment and many similar postnatal environmental influences (described here), twin pairs found in volunteer-based TRA study samples were not “separated at birth” in the way that most people understand this term. The best way to describe this sample is to say that it consisted of partially reared-apart MZ twin pairs.

The Minnesota researchers have always denied access to independent researchers who wanted to inspect the unpublished MISTRA raw data and case history information, and we can safely assume that the volunteer MISTRA MZ twin pairs were no more “reared apart” than were the MZ pairs

Unseen Influences: Race, Gender, and Twins

Steven Fraser, in The Bell Curve Wars, discusses the problems with Hernstein and Murray’s genetic argument for IQ.

He points out that the Flynn effect is particularly devastating. For this reason, he finds it puzzling that they don’t recognize or acknowledge the obvious implications. Black people today are on average smarter, as far as IQ tests go, than white people were a few generations ago. By today’s normed IQ tests, white people of a century ago would now be labeled as “retarded”.

I’ve covered that territory before. What caught my attention the other day was what followed his comments on the Flynn effect. He made a further point about the weakness of the genetics hypothesis. He states that a “remarkable phenomenon commented on in the Moynihan Report of thirty years ago goes unnoticed in The Bell Curve–the prevalence of females among blacks who score high on mental tests” (Kindle Locations 914-925); he continues:

“Others who have done studies of high-IQ blacks have found several times as many females as males above the 120 IQ level. Since black males and black females have the same genetic inheritance, this substantial disparity must have some other roots, especially since it is not found in studies of high-IQ individuals in the general society, such as the famous Terman studies of high-IQ children, which followed these children on into adulthood and later life. If IQ differences of this magnitude can occur with no genetic difference at all, then it is more than mere speculation to say that some unusual environmental effects must be at work among blacks.”

This isn’t limited to any race/ethnicity. It is a gender IQ gap found across diverse other populations.

“However, these environmental effects need not be limited to blacks, for other low-IQ groups of European or other ancestries have likewise tended to have females over-represented among their higher scorers, even though the Terman studies of high-IQ individuals from the general population found no such patterns. One possibility is that females are more resistant to bad environmental conditions, as some other studies suggest. In any event, large sexual disparities in high-IQ individuals where there are no genetic-or socioeconomic-differences present a challenge to both the Herrnstein-Murray thesis and to most of their critics.”

This reminds me of the stereotype threat discussed by Claude M. Steele in Whistling Vivaldi. He shows the research about how much simple changes in environment can cause large changes in results, both for tests of academics and other activities. Women tend to test lower on math, for example. However, neutralize stereotype threat and the disparity disappears.

Environments aren’t just different between populations, but also within populations. The environmental factors that will impact a female are different than for a male, including the stereotypes and expectations placed upon genders just as happens with race. Having much shared genetics doesn’t necessarily mean that all influences are being shared.

To emphasize this point, Fraser extends his argument to an even more stark example. Twins also show great differences, something overlooked by early twin studies.

“Black males and black females are not the only groups with significant IQ differences without any genetic differences. Identical twins with significantly different birth weights also have IQ differences, with the heavier twin averaging nearly nine points higher IQ than the lighter one in some studies.’ This effect is not found where the lighter twin weighs at least six and a half pounds, suggesting that deprivation of nutrition must reach some threshold level before it has a permanent effect on the brain during its crucial early development.”

Slight changes in environment can lead to immense differences over the long term. This is because of the cumulative effect of initial conditions. One thing leads to another. Lowered nutrition or increased toxicity has its impact which gets magnified by such things as school tracking. Each effect becoming a cause and all the causal factors combining to form significant differences in end results.

The Ending of the Nature vs Nurture Debate

The other day, I was directed (by my friend Charles W. Abbot) to an article about cities and ambition. I wrote about that article and this is a continuation of my thoughts. The discussion I’ve had with Charlie has been ongoing and he linked to yet another thoughtful piece. The second article is about the power of environmental influences:

The idea of zero parental influence
by Judith Rich Harris

Harris asks, is this idea dangerous? Is it false?

“A confession: When I first made this proposal ten years ago, I didn’t fully believe it myself. I took an extreme position, the null hypothesis of zero parental influence, for the sake of scientific clarity. Making myself an easy target, I invited the establishment — research psychologists in the academic world — to shoot me down. I didn’t think it would be all that difficult for them to do so. It was clear by then that there weren’t any big effects of parenting, but I thought there must be modest effects that I would ultimately have to acknowledge.

“The establishment’s failure to shoot me down has been nothing short of astonishing. One developmental psychologist even admitted, one year ago on this very website, that researchers hadn’t yet found proof that “parents do shape their children,” but she was still convinced that they will eventually find it, if they just keep searching long enough.”

Her conclusion is damning:

“And what has all this sacrifice and effort on the part of parents bought them? Zilch. There are no indications that children today are happier, more self-confident, less aggressive, or in better mental health than they were sixty years ago, when I was a child — when homes were run by and for adults, when physical punishment was used routinely, when fathers were generally unavailable, when praise was a rare and precious commodity, and when explicit expressions of parental love were reserved for the deathbed.

“Is my idea dangerous? I’ve never condoned child abuse or neglect; I’ve never believed that parents don’t matter. The relationship between a parent and a child is an important one, but it’s important in the same way as the relationship between married partners. A good relationship is one in which each party cares about the other and derives happiness from making the other happy. A good relationship is not one in which one party’s central goal is to modify the other’s personality.

“I think what’s really dangerous — perhaps a better word is tragic — is the establishment’s idea of the all-powerful, and hence all-blamable, parent.”

This past decade, Harris has written two books that I plan on reading:

The Nurture Assumption: Why Children Turn Out the Way They Do

No Two Alike: Human Nature and Human Individuality

She challenges the whole nature versus nurture paradigm. In the first book, she focuses on the nurture side in order to show its true complexity. In the second book, she looks at all the angles.

If you add in the criticisms many others have made of the genetics research, you’ll realize how many of our assumptions have been wrong in this society (I’ve read about this a lot in terms of race and ethnicity). It turns out it is much harder to actually prove genetic correlations are causation.

Take twins for example. There is no way to control for their shared experience in the womb and early childhood. Nutrition, pollution/toxicity, stress, etc has powerful impact on early development, from fetal to childhood development. Plus, there are environmental factors such as growing up in the same class, neighborhood, city, region, etc; there is the shared media influences as well; and there are factors of having the same race and appearances which influences how people treat you.

No one has any realistic conclusion about how much genetics influences twins. We know even less about genetic influences on people in general. There is no doubt genetics plays a role in a very complicated process, but it is clear that beyond some physical traits there are probably few (if any) traits that are directly and/or solely caused by a single gene and nothing else.

Science is in the middle of a paradigm revolution. The centuries old dualistic model of nature vs nurture, especially in the form of genetic determinism vs parental influence, is being shook at its foundation. It no longer is a debate of either/or, but what greater theory that is arising from improved research.

We presently don’t have a language to speak about this developing view. Too much is still up in the air. It will take decades for it to settle out into a new consensus. Until then, we should speak with the utmost care and not let our desire for certainty to overreach what can presently be known.

Some might find this disconcerting or even unacceptable. It isn’t just ideologues who are being challenged. Scientists too are being challenged. All of society is being challenged because the challenge is to the very ground of our human nature. A lot of this research has happened just this past decade and still is barely beginning to filter into mainstream awareness.

Also, it’s going along with a larger shift in our society which I’ve noted before in relation to climate science and biblical studies. Combined with shifts in majorities developing in support of such things as drug legalization/decriminalization, gay marriage, etc and the challenge we face is immense. We are living in an era that might turn out to be equivalent to the Enlightenment Age or the Axial Age. Nothing may remain unturned.

I see these shifts and trends, but I don’t know much more than anyone else. I just pay attention to diverse info and recognize some important changes are happening, however it may add up. Maybe this is part of a greater turning of events or maybe not. That is what makes it exciting. Possibilities are opening up, possibilities of knowledge and possibilities of technology, possibilities of social change and possibilities not yet imagined.

How these possibilities will or will not manifest depends on many things, including our response to them. We could use this opportunity to try to re-create the past, shore up the old order, and salvage what is left of the crumbling paradigm. But that would be a waste of a rare and maybe fleeting opportunity. I’d recommend loosening our grip on perceived certainties and reaching forward into the unknown, the greatest unknown being human nature.

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I noticed two other books I’d like to read by Jay Joseph:

The Gene Illusion – Genetic Research in Psychiatry and Psychology Under the Microscope

The Missing Gene: Psychiatry, Heredity, And the Fruitless Search for Genes