The Invisible Gorilla

In Jordan B. Peterson's 12 Rules for Life: An Antidote to Chaos, he expresses support for the use of corporal punishment and argues that it can be an effective form of discipline. What does the research say? Introduction: 0:00 Quotations: 0:18 Research: 3:45 Contradiction: 5:59 Ending Corporal Punishment: 6:59 Conclusion: 7:56 References: 8:52 References Durrant, J. E., Ensom, R., & Coalition on Physical Punishment of Children and Youth. (2004). Joint statement on physical punishment of children and youth. Ottawa: Coalition on Physical Punishment of Children and Youth. Durrant, J., & Ensom, R. (2012). Physical punishment of children: lessons from 20 years of research. CMAJ, 184(12), 1373-1377. doi:10.1503/cmaj.101314 Gershoff, E. T. (2013). Spanking and child development: We know enough now to stop hitting our children. Child Development Perspectives, 7(3), 133-137. Gershoff, E. T., & Grogan-Kaylor, A. (2016). Spanking and child outcomes: old controversies and new meta-analyses. Journal of Family Psychology, 1-17. doi:10.1037/fam0000191 Global Initiative to End All Corporal Punishment of Children. (2017). Ending legalised violence against children: global progress to December 2017. Author. Retrieved from www.endcorporalpunishment.org/resources/global-reports/global-report-2017.html Mulvaney, M. K., & Mebert, C. J. (2007). Parental corporal punishment predicts behavior problems in early childhood. Journal of Family Psychology, 21(3), 389-397. doi:10.1037/0893-3200.21.3.389 Peterson, J. B. (2018). 12 rules for life: an antidote to chaos. Toronto: Random House Canada. Straus, A, M., Sugarman, D. B., & Giles-Sims, J. (1997). Spanking by parents and subsequent antisocial behavior of children. Arch Pediatr Adolesc Med, 151, 761-767. Vittrup, B., & Holden, G. W. (2010). Children's assessments of corporal punishment and other disciplin ary practices: the role of age, race, SES, and exposure to spanking. Journal of Applied Developmental Psychology, 31, 211-220. doi:10.1016/j.appdev.2009.11.003 Further Reading Afifi, T. O., Ford, D., Gershoff, E. T., Merrick, M., Grogan-Kaylor, A., Ports, K. A., . . . Bennett, R. P. (2017). Spanking and adult mental health impairment: The case for the designation of spanking as an adverse childhood experience. Child Abuse & Neglect, 71, 24-31. Gershoff, E. T., & Bitensky, S. H. (2007). The case against corporal punishment of children. Psychology, Public Policy, and Law, 13(4), 231-272. doi:10.1037/1076-8971.13.4.231

Oh, by the way, I forgot to mention this study by Fontana, Meyer, Klein, and Holloszy (2007). Even endurance athletes running an average of 48 miles a week for 21 years could not compete with sedentary vegans doing less than an hour of exercise a week, with regards to arterial health. References L. Fontana, T. E. Meyer, S. Klein, J. O. Holloszy. Long-term low-calorie low-protein vegan diet and endurance exercise are associated with low cardiometabolic risk. Rejuvenation Res. 2007 10(2):225 - 234.

You're confusing anecdotes with empirical evidence. They're not the same thing. I have no idea why a community that ostensibly values empirical evidence is upvoting this comment. Evidence suggests Paleo diets negate benefits of exercise The problem with the Paleo diet argument

In a recent video, Stef was speaking to a listener about pollution and brought up the issue of sedentary living and its negative effects. First, let me be clear, I am not disputing the negative effects of remaining sedentary for long periods, or the importance of exercise. But Stef, like many others, is vastly inflating the importance of exercise relative to other factors, namely diet. It's a common misconception (70% of people believe) that exercise and diet are both equally important to weight management and weight loss (International Food Information Council Foundation, 2011). This is simply untrue (Flatt, 2011). To quote Dr. Greger: 'What we put in our mouths is most important'. Regarding cancer, literally 5000 hours in the gym can't compete with a plant-based diet. Barnard et al. (2003) compared a group of participants eating a plant-based diet who did moderate exercise (i.e. walking) to another group who did daily, strenuous, hour-long exercise and ate a standard American diet, with a control group. After 14 years, the exercise group were still overweight whereas the diet and exercise group were a healthy weight. More importantly, the participants in the diet and exercise group were roughly twice as effective at fighting cancer growth compared to the exercise group. Another study by Jenkins et al. (2012) showed that consuming a cup a day of beans, chickpeas, or lentils for three months may reduce one's resting heart rate by as much as 250 hours on a treadmill. I strongly urge FDR to shine a light on the importance of diet. I have already posted about nutrition, twice. My first post didn't get much traction but my more recent post seems to have been well-received. References Barnard RJ, Ngo TH, Leung PS, Aronson WJ, Golding LA. Prostate. A low-fat diet and/or strenuous exercise alters the IGF axis in vivo and reduces prostate tumor cell growth in vitro. 2003 Aug 1;56(3):201-6. Flatt JP. Issues and misconceptions about obesity. Obesity (Silver Spring). 2011 Apr;19(4):676-86. International Food Information Council Foundation. 2011. Food & Health Survey: Consumer Attitudes Toward Food Safety, Nutrition & Health. D J Jenkins, C W Kendall, L S Augustin, S Mitchell, S Sahye-Pudaruth, S Blanco Mejia, L Chiavaroli, A Mirrahimi, C Ireland, B Bashyam, E Vidgen, R J de Souza, J L Sievenpiper, J Coveney, L A Leiter, R G Josse. Effect of legumes as part of a low glycemic index diet on glycemic control and cardiovascular risk factors in type 2 diabetes mellitus: a randomized controlled trial. Arch Intern Med. 2012 Nov 26;172(21):1653-60.

Hi AccuTron, it's great to see that you're looking to make some positive dietary changes in your life. However, before you change anything, I would recommend getting a blood test. The reason for this, is that in the future after you've changed your diet, if you get a health check-up and find out you're deficient in a particular nutrient, it may be difficult to know the cause of that deficiency. Someone who doesn't take this precaution may assume his/her change in diet was the cause of a deficiency that they already had, before the change. That's why I think it's good to know what your baseline is before making any changes. As for protein, well, to people who eat a plant-based diet, asking about where to get your protein is akin to asking an anarcho-capitalist "who will build the roads?". Protein is nothing to worry about. In fact, most Americans are far more in need of fiber than protein. Here's Dr. Greger to put you at ease: p.s. I'm happy to answer more of your questions if you have any. I've been eating a plant-based diet for about 7 years.

Essential viewing Description: In this “best-of” compilation of his last four year-in-review presentations, Dr. Greger explains what we can do about the #1 cause of death and disability: our diet. Link to the book: How Not To Die Uprooting the Leading Causes of Death (http://nutritionfacts.org/video/uproo...) More Than an Apple a Day (http://nutritionfacts.org/video/more-...) From Table to Able (http://nutritionfacts.org/video/from-...) Food as Medicine (http://nutritionfacts.org/video/food-...)

Hello Everyone, I made a short presentation (7 min) on corporal punishment. It's unlisted on YouTube, at the moment. The idea was to create a sort of 'pilot' for a YouTube channel called 'PsychologyTube', that I'm thinking about starting in the future. The idea for the channel was somewhat inspired by an existing channel called 'Philosophy Tube'. The presentation style and concept were more appealing to me than the actual content - the presenter is pretty Left-leaning. Anyway, I'd really appreciate some feedback. I think the quality is OK, considering it was created with a smart phone. If, in the future, I can prove to myself and the viewers that I'm capable of making good content, consistently, I will invest in superior audio-visual equipment. Again, this was just a test so any constructive feedback is welcome. Thanks

Here's the Director's Cut, courtesy of Breitbart.

A documentary film about the Clintons based on the book of the same name, by Peter Schweizer. It reminds me very much of the stories told by John Perkins in his book, Confessions of an Economic Hit Man. Just follow the money.

A standard deviation is not 'a bit'. Could you cite some evidence? Also, you hit on one of the issues regarding heritability. Saying the 'environmental factor is 20%' is neither valid nor useful. Joseph (2015) can explain much better than I can so have a look at the hypothetical situation he presents, below. ‘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) References Joseph, J. (2015). The trouble with twin studies: A reassessment of twin research in the social and behavioral sciences. New York: Routledge.

This is just an assertion... Based on this view, the reported Black-White difference in IQ of roughly one standard deviation (Herrnstein & Murray, 1994) is unimportant and increasing Black average IQ scores to match White averages would not be considered a 'significant' change. Similarly, if White IQ scores dropped by a standard deviation due to some unknown environmental factor and became equal to Black scores, this would not be worth mentioning in your view. Do you consider disparities in IQ noteworthy or not? I thought you did, but based on your latest comment, it sounds like you don't. References Herrnstein, R. J., & Murray, C. (1994) The bell curve: Intelligence and class structure in American life. New York: Simon & Schuster

Sorry rosencrantz, I don't understand what you have written. Schiff et al. (1982) doesn't even discuss heritability estimates and I didn't mention them, either. As I said, the study contradicts the view of Jensen (1998) and others that environmental influences can't significantly alter IQ scores. Schiff et al. compared the IQ scores of working class children who were adopted into upper-middle class families with a control group and found the former's scores to be almost a standard deviation higher than the latter's. 'In conclusion, if French children of lower-class parents were reared under exactly the same conditions as the adopted children of our study, they would obtain IQ scores and scholastic results close to those presently observed for up middle-class children. Our observations indicate that, in the population at large, failure is linked with the social class of the parents rather than with the genes they transmit, but these observations only provide ambiguous answers about: genetic differences between children of various social groups. The important point however is that, within the range allowed by our observations and by those of other authors, the answers to these latter questions are not only technically ambiguous but are also of marginal social relevance. We hope that our work will contribute in making more evident the fact that questions concerning the reproduction of social inequalities from one generation to the next cannot be answered by a genetic analysis of IQ scores, and also in making evident the even more important fact that improvements in social conditions could go a long way to ‘boost IQ and scholastic achievement’. (Schiff et al., p. 186-187) I would also like to briefly mention that the concept of heritability is very often misunderstood. There are critics (Joseph, 2004, ch. 5) who argue it should be abandoned, except for use by animal and plant breeders. I'm still trying to get to grips with how to articulate its flaws, myself, so for now I'll just share some critiques that I've found interesting (e.g. Hirsch, 1997; Joseph, 2004; Wahlsten, 1994). References Hirsch, J. (1997). Some history of heredity-vs-environment, genetic inferiority at Harvard (?), and The (incredible) Bell Curve. Genetica, 99(2-3), 207-224. Jensen, A. R. (1998). The g factor. Westport, CT: Praeger. Joseph, J. (2004). The gene illusion. New York. Algora. Schiff, M., Duyme, M., Dumaret, A., & Tomkiewicz, S. (1982). How much could we boost scholastic achievement and IQ scores? A direct answer from a French adoption study. Cognition, 12(2), 165-196. Wahlsten, D. (1994). The intelligence of heritability. Canadian Psychology/Psychologie canadienne, 35(3), 244.

'There is simply no good evidence that social environmental factors have a large effect on IQ, particularly in adolescence and beyond, except in cases of extreme environmental deprivation.' Jensen, 1988, p. 476) Schiff et al. (1982) reported an increase in IQ of almost an entire standard deviation compared to a control group. References Jensen, A. R. (1998). The g factor. Westport, CT: Praeger. Schiff, M., Duyme, M., Dumaret, A., & Tomkiewicz, S. (1982). How much could we boost scholastic achievement and IQ scores? A direct answer from a French adoption study. Cognition, 12(2), 165-196.

Hi rosencrantz, I'm aware that you used 'you' as a general term. Joseph (2004) also has a chapter (ch. 9) on IQ in which he refers to adoption studies. One of the studies he mentions that contradicts the view that IQ cannot be increased was conducted by Schiff et al. (1982). References Joseph, J. (2004). The gene illusion. New York. Algora. Schiff, M., Duyme, M., Dumaret, A., & Tomkiewicz, S. (1982). How much could we boost scholastic achievement and IQ scores? A direct answer from a French adoption study. Cognition, 12(2), 165-196.

Hi RoseCodex, When you say 'major arguments', what are you referring to? Hi Mtt, I'm sure rosencrantz is capable of explaining what he/she was attempting to do, if he/she wishes to do so, and does not need you to speak on his/her behalf. That said, I'm not really sure what 'your terms' is supposed to mean. I labelled the comment as straw-manning because rosencrantz referred to my post by implying I said something I did not say (i.e. that one 'needs' to study reared apart twins in order to measure IQ heritability). If rosencrantz's post was exactly the same but for the sentence about needing to study reared about twins, I would agree with you that the post was just supplying additional information, and would not have labelled it straw-manning. Either way, I still view it as an attempt to subtly dismiss the evidence I had already presented, without actually addressing its contents.

Hi rosencrantz, I did not say you 'need' to study twins reared apart to estimate heritability. Please don't straw-man. I merely quoted Herrnstein and Murray (1994), who view studies of twins reared apart as '‘The most unambiguous direct estimates' (p. 107) of IQ heritability. Joseph (2004) goes into great detail as to why the adoption studies used to support the genetic component in various traits are garbage, too. I recommend you have a look at his critique. I may create another post outlining some of the arguments against the validity of the adoption studies but I'm occupied by other things at the moment. Regardless, the validity of adoption studies doesn't negate the issues with 'reared apart' twin studies, which are commonly used to justify high estimates of IQ heritability. References 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.

Hi Robert, I'm also interested in the intelligence debate. A couple of months ago, I contributed a post to the General Messages section of the forum entitled: The Data Used to Support IQ Heritability Estimates are JUNK. I think you might find it interesting. Let me know what you think. Thanks

YouTube Description: Clinical psychologist Jay Joseph details medical science's 30-year failed quest to find any link between genetics and diagnoses of mental disorders, and debunks widely held beliefs in the psychiatric profession, including the idea of 'genetic predispositions' for mental illness. Jay is the author of The Missing Gene: Psychiatry, Heredity, and the Fruitless Search for Genes and The Gene Illusion: Genetic Research in Psychiatry and Psychology Under the Microscope. http://www.jayjoseph.net/

Thanks for your feedback, Hecatonchire.

Hi Will, Can you explain why?

You reminded me of this: https://youtu.be/ERP4hI7c7NE?t=36

In a recent video, Stef said the following to a listener: 'You have been cursed with knowledge that can save lives. And, what you do with that I don't know but I think if you do nothing with it, that's not good…once you're in possession of that kind of information, rightly or wrongly, you do have some kind of obligation.' (51:30-51:56) Personally, I want liberty-minded, non-violent, rational, critical-thinkers to live long and healthy lives. Thus, allow me to 'curse' FDR with some of the knowledge I’m aware of that has been shown time and time again to save lives. First, let me introduce Michael Greger M.D. who runs NutritionFacts.org and is the best-selling author of How Not To Die: Discover the Foods Scientifically Proven to Prevent and Reverse Disease. He also gave a Google Talk about the book which you can find here. Here’s an excerpt from the book’s synopsis: The vast majority of premature deaths can be prevented through simple changes in diet and lifestyle. In How Not to Die, Dr. Michael Greger, the internationally-renowned nutrition expert, physician, and founder of NutritionFacts.org, examines the fifteen top causes of premature death in America-heart disease, various cancers, diabetes, Parkinson's, high blood pressure, and more-and explains how nutritional and lifestyle interventions can sometimes trump prescription pills and other pharmaceutical and surgical approaches, freeing us to live healthier lives. The simple truth is that most doctors are good at treating acute illnesses but bad at preventing chronic disease. The fifteen leading causes of death claim the lives of 1.6 million Americans annually. This doesn't have to be the case. By following Dr. Greger's advice, all of it backed up by strong scientific evidence, you will learn which foods to eat and which lifestyle changes to make to live longer. History of prostate cancer in your family? Put down that glass of milk and add flaxseed to your diet whenever you can. Have high blood pressure? Hibiscus tea can work better than a leading hypertensive drug-and without the side effects. Fighting off liver disease? Drinking coffee can reduce liver inflammation. Battling breast cancer? Consuming soy is associated with prolonged survival. Worried about heart disease (the number 1 killer in the United States)? Switch to a whole-food, plant-based diet, which has been repeatedly shown not just to prevent the disease but often stop it in its tracks. I’ve often heard Stefan say that it’s irrational to take the advice of a nutritionist, if he, himself, is overweight (sorry I don’t have a source but I do remember him saying this several times). This is because such a nutritionist is either taking his own advice and has become fat, or, is ignoring his own advice and thus doesn’t really believe what he’s selling. Accepting this, I was disheartened to find that the only FDR interview with a nutrition expert (that I’m aware of) was with Robert Lustig; a man who himself is overweight… I want to encourage everyone to read the work of doctors who are both following their own advice and getting healthy, long-term results. Dr. Greger is one such doctor, but there are many more. I’ve included a list of lectures given by such doctors below. Also, here’s a short video contrasting doctors/nutritionists who advocate various diets, with what they actually look like. Uprooting the Leading Causes of Death: https://www.youtube.com/watch?v=30gEiweaAVQ Making Heart Disease History: https://www.youtube.com/watch?v=EqKNfyUPzoU The Best Kept Secret...Ever: https://www.youtube.com/watch?v=HEkQCe7VxUE Tackling diabetes with a bold new dietary approach: Neal Barnard at TEDxFremont: https://www.youtube.com/watch?v=ktQzM2IA-qU If you find this information useful, perhaps the FDR community can encourage Stef to conduct an interview with Dr. Greger about his book. That way, thousands, if not millions, of liberty-minded individuals could gain access to information they may not be aware of; allowing them to live longer and healthier lives. Thank You

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.

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.

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.