Nature vs. Nurture: "Rationality"

==Pro’s Case==R1: Pro explains the Flynn effect by citing better education and a more intellectually stimulating environment, but fails to provide any evidence for these claims. More likely, it is the result of having less malnutrition and disease, both of which can stunt development—this is also why average height has increased over time. [3] This would explain why the Flynn effect has stopped, and perhaps even reversed, in recent years—because those things are no longer an issue in the developed world. [4] [5] This stagnation cannot be explained by Pro’s explanation of the Flynn effect—has our education system declined and the world become less stimulating over the past few decades? So while environmental factors may have played a large role in the past, when we were much poorer, they don’t anymore.R2: If Pro’s claim about the environmental influences on child brain development were correct, surely there would be some evidence of it in twin and adoption studies. But there isn’t. [1] [2] Why, if this sort of environmental influence is so important, are the IQs of twins raised by different families pretty much the same as twins raised together?Pro claims that meditating physically changes people’s brains, as does practicing other skills like music and juggling. But this proves nothing. Practicing something makes you better at that specific thing, but that isn’t the same as improving intelligence or conscientiousness. Pro claims that meditators are “masters of conscientiousness”—but provides no evidence of this claim. This sort of claim requires proof, not just intuitive appeal. Even if you accept that meditation can improve conscientiousness, you’d need some sort of scientific study to measure the effect, to show whether it is a large or small effect.IQ can vary a lot during childhood, but still has substantial genetic influence—probably around .45 heritability. [6] And then environmental influences disappear after adolescence. Note that this doesn’t mean that a good environment can raise IQ during childhood, and then that raised IQ sticks after you become an adult. You revert to your genetic potential whether your family environment raised or lowered your IQ during childhood—this is shown by twin studies. During their childhood, twins raised apart may have had very different IQs—but once they became adults, such changes disappeared, and their IQs converged, going back to a .76 correlation. [2] Since environment is, at most, only slightly more important than genes during childhood, and much less important than genes during adulthood (in which we spend most of our lives), genes are, on balance, more important than environment for intelligence. R3: If the results of this program were really caused by changing environmental factors, then surely such benefits would show up in other early intervention programs, like Head Start. But according to the Department of Health and Human Services, “Once the children enter school there is little difference between the scores of Head Start and control children. . . Findings for the individual cognitive measures—intelligence, readiness and achievement—reflect the same trends as the global measure. . . By the end of the second year there are no educationally meaningful differences on any of the measures.” [7] The differences in IQ in the Abecedarian Project emerged at 6 months of age—1.6 months after the mean entrance age of 4.4 months—then stayed constant during the rest of the program’s intervention, until age 5, and beyond. [8] Which seems more likely—that the Abecedarian project caused permanent IQ differences, while other early intervention programs couldn’t, after just 1.6 months in the program, and then was unable to make more improvements during the next several years of the program, or that the two groups had genetic differences in IQ before the program?R4: The variability over a person’s lifetime is different from the variability between people. This is an important distinction. The study Pro cites is about how much a person’s intelligence changes over their life. Imagine that there are only 4 genes that affect IQ. People with the A gene have an average IQ of 115, and people with the B gene have an average IQ of 85. People with the C gene have a slightly wider IQ variance over their life, and people with the D gene have a slightly narrower IQ variance over their life. People have either AC, AD, BC, or BD. Imagine that environment can affect your IQ 5 points over your lifetime. Since the C and D genes affect the change over a lifetime so little, environment can play a larger role in the change over a person’s lifetime than genes, even if it plays a small role overall. Supporting this is the fact that people’s IQ doesn’t change very much over their lifetime.==My Case==C1: Heritability of IQBy adulthood, adopted siblings aren’t more similar in IQ than any 2 random strangers picked from the population. [1] The correlation of IQ between identical twins raised together is .86, compared to .76 for identical twins raised apart. [2] C2: Heritability of ConscientiousnessThe heritability of conscientiousness is estimated to be .18-.49. [10] The effect of shared environment (family environment) is negligible, and ‘unique environment’ accounts for the rest. [10]C3: Shared Environment vs. Unique Environment‘Shared environment’ is what most people mean by ‘nurture.’ It is everything adopted siblings living in the same home would have in common—parents, school, socioeconomic status, neighborhood, etc. ‘Unique environment’ is everything that isn’t genes or shared environment—which means that it doesn’t imply environmental influence. The burden of proof is on Pro to show that ‘unique environment’ means environmental influences. I contend that for traits like conscientiousness, much of ‘unique environment’ is individual choice. Much of how responsible and careful you are isn’t ‘determined’ by outside influences, but rather is just something you choose to be. I challenge Pro to provide a specific part of an environment that he thinks accounts for ‘unique environment.’ All of the environmental influences he has named so far are part of ‘shared environment’—which has little measured effect.==Sources==[1] Bouchard TJ (April 1998). "Genetic and environmental influences on adult intelligence and special mental abilities". Hum. Biol. 70 (2): 257–79.[2] Scarr S. 1997. Behavior genetic and socialization theories of intelligence: truce and reconciliation. In R. J. Sternberg & E. Grigorenko (Ed.), Intelligence, Heredity, and Environment (pp. 3-41).[3] www.econ.upf.edu/docs/seminars/baten.pdf[4] Cotton, S. M.; Kiely, P. M.; Crewther, D. P.; Thomson,, B.; Laycock, R.; Crewther, S. G. (2005). "A normative and reliability study for the Raven's Colored Progressive Matrices for primary school aged children in Australia". Personality and Individual Differences 39: 647–660.[5] Sundet, J.; Barlaug, D.; Torjussen, T. (2004). Intelligence 32 (4): 349–362.[6] Neisser, U.; Boodoo, G.; Bouchard, T. J. , J.; Boykin, A. W.; Brody, N.; Ceci, S. J.; Halpern, D. F.; Loehlin, J. C. et al. (1996). "Intelligence: Knowns and Unknowns". American Psychologist 51: 77.[7] Ruth McKey et al., “The Impact of Head Start on Children, Families, and Communities,” U.S. Department of Health and Human Services, HHS 85–31193, June 1985. p8-11. [8] Spitz, “Some Questions about the Results of the Abecedarian Early Intervention Project Cited by the APA Task Force on Intelligence,” p.72.[9] Spitz, “Does the Carolina Abecedarian Early Intervention Project Prevent Sociocultural Mental Retardation?”: pp.228–229[10] http://genepi.qimr.edu.au...