The Data Used to Support IQ Heritability Estimates are JUNK

[The Invisible Gorilla]

Herrnstein and Murray (1994) estimate that ‘the genetic component of IQ is unlikely to be smaller than 40 percent or higher than 80 percent’ (p. 105). And claim that ‘The most unambiguous direct estimates, based on identical twins reared apart, produce some of the highest estimates of heritability.’ (p. 107). Moreover, they say that: ‘The purest of the direct comparisons is based on identical (monozygotic, MZ) twins reared apart, often not knowing of each other’s existence. Identical twins share all their genes, and if they have been raised apart since birth, then the only environment they shared was that in the womb. Except for the effects on their IQs of the shared uterine environment, their IQ correlation directly estimates heritability.’ (p. 107)

 

This ideal scenario of reared-apart twin research, put forth by Herrnstein and Murray (1994), is far from the reality of what actually occurs in studies of reared apart twins. The use of the term ‘reared apart’ is highly problematic in and of itself. Put simply, most twins ‘reared-apart’, aren’t reared apart for significant portions of their developing lives. Jay Joseph (2015) evaluated some of the most well-known twin studies and I will be relying heavily on his work to justify this claim.

 

The first twins reared-apart (TRA) study was conducted by Newman, Freeman, and Holzinger (1937, cited in Joseph, 2015) and included 19 pairs of monozygotic twins reared-apart (MZA). Here’s Joseph’s summary of each pair:

 

‘the MZA age of separation ranged from 3 weeks to 6 years, and pairs often grew up in the same town or region. Rather than being “separated,” many pairs had regular and prolonged contact and, more importantly, had a relationship with each other. For example, Pair I corresponded with each other and had been living together for 1 year when studied; Pair II had lived and worked together for 5 years; Pair IV had visited each other all their lives; Pair V lived together for 1 year and had visits and were regularly in correspondence; Pair VI was in regular contact their entire adult life and were living together at age 58 when studied; Pair VII had annual visits; Pair IX lived 3 miles apart and saw each other regularly; Pair XII had seen each other often for 5 years leading up to the study; Pair XIII visited each other regularly in the years leading up to the study; Pair XIV corresponded and tried to spend a few weeks per year with each other for the 15 years leading up to the study; and Pair XIX was reared together for the first 6 years of life and studied nursing together at age 17.’ (p. 24 & 28)

 

Shields (1962, cited in Joseph, 2015) published the second TRA study which included 44 MZA pairs. Again, Joseph summaries the supposedly ‘reared-apart’ twins:

 

‘Examples from Shields’ case descriptions of the 44 MZA pairs seen in Table 2.2 include, “have always been closely attached to each other,” “have been in business together for the past 8 years,” “were in cottages next door to one another and attended the same school,” “went to school together,” “came home to mother at 14,” “ were dressed alike . . . . They attended the same school,” “met about once a fortnight during adolescence,” “brought up within a few hundred yards from one another,” “met about twice a week and sometimes spent holidays together,” “met regularly,” “now correspond frequently and meet at holidays,” “until [separation at age 8] the twins had done everything together,” “formed an extremely close association,” “brought up together till the age of 7,” “were reunited most of the time from 5 to 15,” “were closely attached and went about a lot together,” “became very close . . . . they are mutually dependent,” “After reunion [at age 5] in the parental home the twins went to private schools together until [age 17],” and “lived a few roads away from each other in the same northern industrial town. They were dressed alike.”’ (p. 30-31)

 

Juel-Nielson (1965, cited in Joseph) studied 12 MZA pairs without using a control group. Here is Joseph’s summary of the twins:

 

‘age at separation ranged from 1 day to almost 6 years, and 5 of the 12 pairs spent at least the first year of life together. In addition, Pair IV (“Ingegerd & Monika”) was reared together with their mother between the ages of 7 and 14. Several pairs had a close relationship and years of mutual contact. Each of the 12 case histories Juel-Nielsen presented contained a section called “The Twin Relationship,” which should not be found in a study of “reared-apart” twins where the common perception is that twins were separated at birth and had never met, and therefore had no relationship with each other. Most twins in this study grew up in impoverished rural or urban environments. This restricted range of rearing environments added an additional important similarity-producing bias to the study.’

 

The Minnesota Study of Twins Reared Apart (MISTRA) is the most well-known TRA study. It’s been referenced in many popular books including Pinker’s The Blank Slate (2002) and Ridley’s Nature Via Nurture (2003). One of the MISTRA’s researchers, Nancy Segal, was interviewed on FDR last year. Segal authored Born Together – Reared Apart (2012), which discusses the findings of the MISTRA. As you may by now be able to guess, the use of the term ‘reared apart’ in her book title is far from accurate. As Joseph (2015) notes, the MISTRA ‘consisted mainly of MZA pairs only partially reared apart, most of whom grew up reared together—at the same time—in similar social, political, and cultural environments.’ (p. 103).

 

The facts about the TRA study samples enumerated above clearly conflict with reasonable conceptions of what it means to be ‘reared apart’. Joseph (2015) also evaluates other TRA studies in his book, citing similar flaws.

 

To come back to The Bell Curve (1994) for a moment, what is concerning about Herrnstein and Murray’s work, is that they do not appear to mention any of the issues regarding the use of the term ‘reared apart’ as it relates to twin studies. In fact, their section devoted to genetics and IQ is only about 4 pages long (see p. 105-108).

 

The sad fact is that the mislabelling of these twin studies as ‘reared apart’ is just the tip of the iceberg with regards to their flaws. Below is a partial list of TRA study issues and biases discussed by critics, summarised by Joseph (2015):

• Many twin pairs experienced late separation, and many pairs were reared together in the same home for several years
• Most twin pairs grew up in similar socioeconomic and cultural environments
• MZA correlations were inflated by non-genetic cohort effects, based on common age, common sex, and other factors
• Twins share a common pre-natal (intrauterine) environment, and the MZA pre-natal environment is more similar than the DZA pre-natal environment
• TRA study findings might not be (or are not) generalizable to the non-twin population
• In studies based on volunteer twins, a bias was introduced because pairs had to have known of each other’s existence to be able to participate in the study
• MZA samples were biased in favor of more similar pairs, meaning that studied MZA pairs are not representative of MZAs as a population
• The similar physical appearance and level of attractiveness of MZAs will elicit more similar behavior-influencing treatment by their social environments
• Twins sometimes had financial and other types of incentives to exaggerate or lie about their degree of separation and behavioral similarity, and their accounts are not always reliable
• There were several questionable or false assumptions underlying the statistical procedures used in the studies
• MZA pairs were not assigned to random environments
• There was researcher bias in favor of genetic interpretations of the data
• There were problems with the IQ and personality tests used
• The validity of concepts such as IQ, personality, and heritability are questionable
• In cases where evaluations and testing were performed by the same person, there was a potential for experimenter bias in favor of twin similarity
• A registry should be established to house raw TRA study data, which should be made available for independent inspection and analysis

I encourage everyone who is interested in the topic of individual differences (including IQ) to read about the flaws in twin research. This research method has become the foundation of a lot of behavioural genetics research but it is deeply flawed. It seems that most critics of behavioural genetics are labelled as left-leaning, PC egalitarians who think that identifying differences in race, IQ, etc. is prejudicial. That may be so, but you don’t have to be a PC lefty to be sceptical of the conclusions drawn by behavioural geneticists. As Joseph (2015) has demonstrated, there is a plethora of reasons to doubt their conclusions (e.g. IQ heritability estimates).

 

I recommend Joseph’s books The Trouble with Twin Studies (2015) and The Gene Illusion (2004), which I have referenced below. If you’d prefer not to read a whole book on the subject, Joseph also blogs at Mad in America (created by Robert Whitaker, of whom many of you may be familiar), where you can find several articles that concisely explain his arguments against the validity of twin studies.

 

References

Herrnstein, R. J., & Murray, C. (1994) The Bell Curve: Intelligence and Class Structure in American Life. New York: Simon & Schuster

 

Joseph, J. (2015). The trouble with twin studies: A reassessment of twin research in the social and behavioral sciences. Routledge.

 

Pinker, S. (2002). The blank slate: The modern denial of human nature. Penguin.

 

Ridley, M. (2003). Nature via nurture: Genes, experience, and what makes us human. HarperCollins.

 

Segal, N. L. (2012). Born together—reared apart: The landmark Minnesota twin study. Harvard University Press.

 

 

Also see:

 

Joseph, J. (2004). The Gene Illusion. New York. Algora.

 

The Trouble with Twin Studies (Featured Blog): http://www.madinamerica.com/2013/03/the-trouble-with-twin-studies/

 

Studies of Reared-Apart (Separated) Twins: Facts and Fallacies (Featured Blog): http://www.madinamerica.com/2014/12/studies-reared-apart-separated-twins-facts-fallacies/

 

“Bewitching Science” Revisited: Tales of Reunited Twins and the Genetics of Behavior (Featured Blog): http://www.madinamerica.com/2016/03/bewitching-science-revisited-tales-of-reunited-twins-and-the-genetics-of-behavior/

[Will Torbald]

Doubt! Problematic! Skepticism! I was hoping for a conclusion at the end but all I got was buzzwords. Are there twin studies that have opposite conclusions instead of throwing the word "questionable" as if it meant anything?

[aviet]

Is there a point you are trying to make here beyond the questionable validity of research into IQ heritability? I was expecting some info on the extent genetics play a role in IQ.

It is clear that genetics play a huge role in IQ, i.e. Down's syndrome sufferers are obviously not well disposed to gain high IQs. I don't think race plays much of a role in IQ though. The average IQ in India is given as around 82, but the average IQ of students with Hindu and Sikh background in the UK was 102. That would be a jump of twenty points. Though I think if you could assess the IQs of their immigrant ancestors, they would have been above average. As such I don't give much credence to the regression to the mean argument.

As for the average black American IQ of 85. I don't think it's much of a surprise that it would be so low with levels of violence, family breakdown, drugs etc. If you assessed white IQs in the south I'm sure you'd find lower IQs than in the north.

There are some interesting questions in relation to race though. My main observation is the relative roaring success of northern European and Mongoloid societies and to a lesser extent Southern European societies; yet African societies in particular have been despotic, crime-ridden failures. Why were Mongoloid societies able to make such great leaps (albeit largely copying western societies) and others unable to? Another observation is the success of Estonia (average IQ 98) post-Communism compared to the often lackluster paths of their other former-red and lower IQ brethren.

[Will Torbald]

Is there a point you are trying to make here beyond the questionable validity of research into IQ heritability? I was expecting some info on the extent genetics play a role in IQ.

 

It is clear that genetics play a huge role in IQ, i.e. Down's syndrome sufferers are obviously not well disposed to gain high IQs. I don't think race plays much of a role in IQ though. The average IQ in India is given as around 82, but the average IQ of students with Hindu and Sikh background in the UK was 102. That would be a jump of twenty points. Though I think if you could assess the IQs of their immigrant ancestors, they would have been above average. As such I don't give much credence to the regression to the mean argument.

 

As for the average black American IQ of 85. I don't think it's much of a surprise that it would be so low with levels of violence, family breakdown, drugs etc. If you assessed white IQs in the south I'm sure you'd find lower IQs than in the north.

 

There are some interesting questions in relation to race though. My main observation is the relative roaring success of northern European and Mongoloid societies and to a lesser extent Southern European societies; yet African societies in particular have been despotic, crime-ridden failures. Why were Mongoloid societies able to make such great leaps (albeit largely copying western societies) and others unable to? Another observation is the success of Estonia (average IQ 98) post-Communism compared to the often lackluster paths of their other former-red and lower IQ brethren.

 

If the average in India is 82, and the average in the UK is 102 for students, that only means that the smart Indians are the ones leaving for the UK and the not so smart are staying. If you look at the bell curve charts for race and IQ you'll see a similar pattern, but displaced for each race with blacks as a group lagging behind hispanics, whites, and east asians.

[EclecticIdealist]

Doubt! Problematic! Skepticism! I was hoping for a conclusion at the end but all I got was buzzwords. Are there twin studies that have opposite conclusions instead of throwing the word "questionable" as if it meant anything?

Let me summarize for you.  Those citing MZA Twin studies as strong evidence nature vs nurture as having the most significant influence on intelligence are failing to account for the substantially similar environments which the twins the in the study were raised under. While the environments were not identical, they were sufficiently similar in socio-economic status and other environmental factors to fail to provide any significant contrast of environments to either prove or disprove the contention. Essentially, the studies do not actually entail the substantial differences in environment necessary to prove the superior force of nature vs nurture that is being put forth by those favoring such an argument.

[Will Torbald]

Let me summarize for you.  Those citing MZA Twin studies as strong evidence nature vs nurture as having the most significant influence on intelligence are failing to account for the substantially similar environments which the twins the in the study were raised under. While the environments were not identical, they were sufficiently similar in socio-economic status and other environmental factors to fail to provide any significant contrast of environments to either prove or disprove the contention. Essentially, the studies do not actually entail the substantial differences in environment necessary to prove the superior force of nature vs nurture that is being put forth by those favoring such an argument.

 

If there are twins that shared similar lives even if apart, and some who had different lives - then every study would have immediately noticed that when they gathered the data and saw wildly disparate IQ among twins. But that's not the case. In those who had similar lives, similar IQ is had. In those with not so similar life, similar IQ too. If the nature and genetics argument was so weak that it would all be a result of faulty data - and that the opposite is true, that it's mostly nature - then most if not all studies would have already shown to be true. What I asked for, twin studies with the opposite result would be interesting instead.

[The Invisible Gorilla]

Doubt! Problematic! Skepticism! I was hoping for a conclusion at the end but all I got was buzzwords. Are there twin studies that have opposite conclusions instead of throwing the word "questionable" as if it meant anything?

 

 

Hi Will

 

You don’t find the fact that significant numbers of twins included in TRA studies are not actually reared apart and researchers such as Herrnstein and Murray (1994) don’t even bother to mention this when presenting estimates of IQ heritability, somewhat problematic? Despite their claim that studies of twins reared apart are the ‘most unambiguous direct estimates’ (p. 107) of IQ heritability.

 

You asked for examples of twin studies that conflict with the findings presented in some of the more well-known and cited TRA studies. Providing conflicting evidence is not necessary in order to criticise a research method. The findings are not important if the research method used to acquire the data is deeply flawed. It’s ‘garbage in, garbage out’, as they say.

 

Finally, I think you may have missed the point of my post. It does not aim to conclude anything. Rather, it aims to arouse scepticism in readers who accept the heritability estimates put forward by researchers such as Herrnstein and Murray (1994). I shared some evidence that demonstrates how the label ‘reared apart’ is inaccurate and arguably, disingenuous; in addition to Joseph’s (2015) partial summary of other problems with the twin research method. Which I hope will inspire readers to delve deeper into the research literature, some of which I provided at the end of the post.

[The Invisible Gorilla]

Is there a point you are trying to make here beyond the questionable validity of research into IQ heritability? I was expecting some info on the extent genetics play a role in IQ.

 

It is clear that genetics play a huge role in IQ, i.e. Down's syndrome sufferers are obviously not well disposed to gain high IQs. I don't think race plays much of a role in IQ though. The average IQ in India is given as around 82, but the average IQ of students with Hindu and Sikh background in the UK was 102. That would be a jump of twenty points. Though I think if you could assess the IQs of their immigrant ancestors, they would have been above average. As such I don't give much credence to the regression to the mean argument.

 

As for the average black American IQ of 85. I don't think it's much of a surprise that it would be so low with levels of violence, family breakdown, drugs etc. If you assessed white IQs in the south I'm sure you'd find lower IQs than in the north.

 

There are some interesting questions in relation to race though. My main observation is the relative roaring success of northern European and Mongoloid societies and to a lesser extent Southern European societies; yet African societies in particular have been despotic, crime-ridden failures. Why were Mongoloid societies able to make such great leaps (albeit largely copying western societies) and others unable to? Another observation is the success of Estonia (average IQ 98) post-Communism compared to the often lackluster paths of their other former-red and lower IQ brethren.

 

Hi aviet64

 

Firstly, I’m not sure why you mentioned IQ test scores. IQ scores, alone, can’t tell you anything about IQ heritability. All they can do is show variations in population scores. They can’t tell you what caused the variation. That’s why twin studies exist; their ostensible purpose is to separate genetic and environmental factors. However, in large part, they fail to do this for a variety of reasons, some of which I covered in my original post.

 

Saying genetics ‘play a huge role in IQ’ is a vague and not particularly useful statement. Genes do not typically act in isolation. They interact with the environment. The most common example I know of to explain why focusing on genes in isolation is not helpful is the case of phenylketonuria (PKU). PKU is a heritable single-gene disorder that causes mental retardation. However, if an at-risk infant is given a low-phenlyalanine diet during early development, the disorder will be prevented from causing mental retardation.

 

Joseph (2015) also presents an instructive hypothetical situation:

 

‘As an example of how heritability estimates do not measure the “strength” or “magnitude” of genetic influences, imagine a country in which all citizens (100 percent) carry the gene predisposing them to favism, a disease marked by the development of hemolytic anemia. Favism is caused by an inherited deficiency of glucose-6-phosphate located on the X chromosome, combined with the consumption of fava (broad) beans or the inhalation of fava bean pollen. In other words, both “beans and genes” are necessary for favism to appear. Let us then imagine that 3 percent of the citizens, all of whom are of course genetically predisposed to develop favism, consume fava beans and are subsequently diagnosed with favism. In this case, because all citizens carried the gene but only some ate fava beans, all favism variation in the population would be caused by environmental factors (fava bean exposure), and the heritability of favism therefore would be zero (0.0). Even though favism heritability would be 0 percent in this example, it obviously would be mistaken to conclude that genes play no role in developing the disorder, or that the genetic influence was weak or irrelevant. A genetic predisposition is, in fact, a prerequisite for developing favism.

 

On the other extreme, if all citizens ate a diet that included fava beans but only some carried the gene, all favism variation would now be caused by genetic factors (carrying or not carrying the gene), and the heritability of favism would be 100 percent (1.0). As we see, heritability estimates assess variation as opposed to cause, and do not indicate the “strength” of the genetic influence (Moore, 2013).2

 

As another example, imagine a society where everyone (like MZ twin pairs) is born with identical genotypes. In such a society, all variation in intelligence and behavior would be caused by environmental factors, meaning that the heritability of all behavioral characteristics, psychiatric disorders, medical conditions—basically everything—would be zero. Once again, population variation and cause are different concepts.’ (p. 79)

 

I hope this helps and please correct me if I have made errors. I also want to thank you for your interest in this topic. I am still a student of the literature and by no means wish to portray myself as an authority in this area of inquiry. I want our discussion of this topic to be as educational for me as I hope it is for you and other readers.

[vahleeb]

Hi Will

 

You don’t find the fact that significant numbers of twins included in TRA studies are not actually reared apart and researchers such as Herrnstein and Murray (1994) don’t even bother to mention this when presenting estimates of IQ heritability, somewhat problematic? Despite their claim that studies of twins reared apart are the ‘most unambiguous direct estimates’ (p. 107) of IQ heritability.

 

You asked for examples of twin studies that conflict with the findings presented in some of the more well-known and cited TRA studies. Providing conflicting evidence is not necessary in order to criticise a research method. The findings are not important if the research method used to acquire the data is deeply flawed. It’s ‘garbage in, garbage out’, as they say.

 

Finally, I think you may have missed the point of my post. It does not aim to conclude anything. Rather, it aims to arouse scepticism in readers who accept the heritability estimates put forward by researchers such as Herrnstein and Murray (1994). I shared some evidence that demonstrates how the label ‘reared apart’ is inaccurate and arguably, disingenuous; in addition to Joseph’s (2015) partial summary of other problems with the twin research method. Which I hope will inspire readers to delve deeper into the research literature, some of which I provided at the end of the post.

 

 

Hi TIG,

 

I think the part that is missing from your presentation is wether or not Murray & Herrnstein's 1994 book is referencing the very same studies debunked by Joseph or not. If you had that, you'd have a bulletproof case.

 

Personally, I think that the conclusion that IQ is a predominantly genetic trait is extremely counterintuitive, however, since the discovery of the "warrior-gene" that Stef references at the end of this presentation: 

 I have to give a larger leniency as to genetic theories.

[Will Torbald]

Hi Will

 

You don’t find the fact that significant numbers of twins included in TRA studies are not actually reared apart and researchers such as Herrnstein and Murray (1994) don’t even bother to mention this when presenting estimates of IQ heritability, somewhat problematic? Despite their claim that studies of twins reared apart are the ‘most unambiguous direct estimates’ (p. 107) of IQ heritability.

 

You asked for examples of twin studies that conflict with the findings presented in some of the more well-known and cited TRA studies. Providing conflicting evidence is not necessary in order to criticise a research method. The findings are not important if the research method used to acquire the data is deeply flawed. It’s ‘garbage in, garbage out’, as they say.

 

Finally, I think you may have missed the point of my post. It does not aim to conclude anything. Rather, it aims to arouse scepticism in readers who accept the heritability estimates put forward by researchers such as Herrnstein and Murray (1994). I shared some evidence that demonstrates how the label ‘reared apart’ is inaccurate and arguably, disingenuous; in addition to Joseph’s (2015) partial summary of other problems with the twin research method. Which I hope will inspire readers to delve deeper into the research literature, some of which I provided at the end of the post.

Hi Gorila.

 

Um, no I don't.

[The Invisible Gorilla]

Hi TIG,

 

I think the part that is missing from your presentation is wether or not Murray & Herrnstein's 1994 book is referencing the very same studies debunked by Joseph or not. If you had that, you'd have a bulletproof case.

 

Personally, I think that the conclusion that IQ is a predominantly genetic trait is extremely counterintuitive, however, since the discovery of the "warrior-gene" that Stef references at the end of this presentation: 

 I have to give a larger leniency as to genetic theories.

 

Hi vahleeb, thanks for requesting clarification on this.

 

Most of the citations included in Herrnstein and Murray’s (1994) small section on genetics are secondary sources. In other words, they are references to reviews of the research literature (e.g. Bouchard, 1981; Plomin & Defries, 1980; Plomin & Loehlin, 1989) or to textbooks (Falconer, 1989) and books (Snyderman & Rothman, 1988). Feel free to have a look at these but if you’re interested in primary sources, they only cite two; the MISTRA (Bouchard et al. 1990) and the Swedish Adoption/Twin Study of Aging (SATSA) (Pedersen et al., 1992). I covered the MISTRA in my original post, although I recommend reading Joseph (2015), who devotes two whole chapters to dissecting its myriad flaws. I didn’t mention the SATSA in my original post because its problems are similar to those highlighted in the other twin studies.

 

Joseph (2015) summing-up the SATSA:

 

‘In the Swedish study the investigators considered pairs to be “reared apart” if they had been separated before age 11: “By definition, the twins reared apart were separated by the age of 11” (Pedersen, Plomin, Nesselroade, & McClearn, 1992, p. 347). About 75 percent had some degree of contact after separation. According to the researchers, the SATSA twins (average age 65.6 years) were “separated” for an average of only 10.9 years at the time of testing (Pedersen et al., 1992, p. 347). Twins supplied information by mail, and many were not investigated personally (for other major problem areas of the SATSA, see Kamin &Goldberger, 2002). Bouchard saw his study as superior to the SATSA in several respects: “Their instruments are very inferior to ours . . . . Their zygosity diagnosis is entirely by questionnaire and their data collected by mail” (Bouchard, 1993b, p. 26).’ (p. 11)

 

Also, to put into context the influence of the MISTRA, according to Google Scholar, it has been cited 1603 times. Compare this to the SATSA, published only a couple of years later, which has only been cited 349 times.

 

There’s one more thing I’d like to highlight. On page 107 of The Bell Curve (1994), Herrnstein and Murray write:

 

‘Direct estimates are based on samples of blood relatives who were raised apart. Their genetic overlap can be estimated from basic genetic considerations. The direct methods assume that the correlations between them are due to the shared genes rather than shared environments because they do not, in fact, share environments, an assumption that is more or less plausible, given the particular conditions of the study.’

 

Notice the use of the words ‘assume’ and ‘more or less plausible’. Twin studies do make a plethora of assumptions that have been challenged for decades (most notably the ‘equal environment assumption’) and are discussed by Joseph (2015) but if you’re going to write a whole book arguing that genetics play a key role in intelligence, I expect more than the offer of ‘more or less plausible’ to support the research method that Herrnstein and Murray, themselves, say supplies the ‘most unambiguous direct estimates’ (p. 107) of IQ heritability. Again, they don’t bother to mention any of the flaws or consider the problems with the assumptions that twin research methods make.

 

Regarding genetics and crime, Joseph (2004) has a whole chapter on the subject, which I recommend. He states that ‘apart from claims made about Brunner and colleagues’ 1993 study of one Dutch family, no genes have been found to cause criminal or antisocial behavior’ (p. 275) (Brunner et al., 1993; Rowe, 2002; Wassermann & Wachbroit, 2001. For a review of the “XYY fiasco,” see Hubbard & Wald, 1993, cited in Joseph, 2004). I would have to look at his sources myself before I could say anymore, but if Joseph is correct then obviously the evidence in favour of a genetic basis for crime is severely lacking.

 

References

 

Bouchard, T. J., & McGue, M. (1981). Familial studies of intelligence: A review. Science, 212(4498), 1055-1059.

 

Bouchard, T. J., Lykken, D. T., McGue, M., Segal, N. L., & Tellegen, A. (1990). Sources of human psychological differences: The Minnesota study of twins reared apart. Science, 250(4978), 223-228.

 

Falconer, D. S. 1989. An Introduction to Quantitative Genetics. 3d ed. New York: Wiley.

 

Herrnstein, R. J., & Murray, C. (1994) The Bell Curve: Intelligence and Class Structure in American Life. New York: Simon & Schuster

 

Joseph, J. (2004). The Gene Illusion. New York. Algora.

 

Joseph, J. (2015). The trouble with twin studies: A reassessment of twin research in the social and behavioral sciences. Routledge.

 

Pedersen, N. L., Plomin, R., Nesselroade, J. R., & McClearn, G. E. (1992). A quantitative genetic analysis of cognitive abilities during the second half of the life span.

Psychological Science, 3(6), 346-353.

 

Plomin, R., & DeFries, J. C. (1980). Genetics and intelligence: Recent data. Intelligence, 4(1), 15-24.

 

Plomin, R., & Loehlin, J. C. (1989). Direct and indirect IQ heritability estimates: a puzzle. Behavior Genetics, 19(3), 331-342.

 

Snyderman, M., & Rothman, S. 1988. The IQ Controversy: The Media and Public Policy. New Brunswick, N.J.: Transaction Books.

[The Invisible Gorilla]

Hi Gorila.

 

Um, no I don't.

 

Hi Will,

 

Can you explain why?

[Hecatonchire]

Doubt! Problematic! Skepticism! I was hoping for a conclusion at the end but all I got was buzzwords. Are there twin studies that have opposite conclusions instead of throwing the word "questionable" as if it meant anything?

 

You can't reach a conclusion without evidence. If the evidence is shown to be faulty, then conclusions need to be withdrawn until there is sufficient evidence to arrive at a conclusion.

 

Nice post, Gorilla. I wasn't aware of the problems in twin research. Nobody gives enough credit to people that actually follow the scientific method's peer-review process. Like that recent caller that was talking about corruption in science, everyone just wants conclusions and wants to jump to the end and get their money. There's often very little reward for testing to see if other published works are accurate or not. Kudos.

[The Invisible Gorilla]

You can't reach a conclusion without evidence. If the evidence is shown to be faulty, then conclusions need to be withdrawn until there is sufficient evidence to arrive at a conclusion.

 

Nice post, Gorilla. I wasn't aware of the problems in twin research. Nobody gives enough credit to people that actually follow the scientific method's peer-review process. Like that recent caller that was talking about corruption in science, everyone just wants conclusions and wants to jump to the end and get their money. There's often very little reward for testing to see if other published works are accurate or not. Kudos.

 

Thanks for your feedback, Hecatonchire.