The fact that we all understand and accept that Shaq is 7'1" tall, but that we can't be mentally different through genetics is entirely absurd.<br><br>It seems elementary to me.,(reply>), @Jis Si  I think you’re confusing “easy” and “simple”. When I stated that genetic explanations are easy to make, I wasn’t making any claims about the simplicity of the theory itself. A claim can be easy to make, and yet, not be a simple theory. For instance, it’s easy to explain any unexplained phenomena by claiming that god did it, but that doesn’t make the god hypothesis a simple theory.,(reply>), @Donald Taylor  “genetic explanations are generally the easiest explanations to make, and they should therefore be viewed with suspicion.”<br>No, the easiest explanations should be the default! Have you heard of Occam’s razor? The explanation with the least amount of assumptions (i.e. the simplest one) is most likely true! You have it totally backwards there,(reply>), @Dale Rohling first off, i would like to thank you as well for the good natured exchange. <br><br>to your second point, i do acknowledge that genetics plays a role in intelligence. that being said, the claim i’m making is that we don’t know if the variation that we observe is the result of genetics or non-genetic factors. and this leads to your first point. i think that the intelligence literature too narrowly defines the concept of “environment”. even within a shared environment, the non-genetic influences could be drastically different. <br><br>for example, in my own case, which i do not think is unusual, illustrates the issue. to the outside observer, my brother and i share an environment, that is, we grew up in the same household and attended the same schools. however, our teachers were different, our friends and peers were different, we were even treated differently by our families, and not because our genes caused us to behave differently, which then in turn causes people to treat us differently, as Murray suggests, but merely because i was older and was therefore held to a different standard. and these are but a few examples, but i will not belabor the point. <br><br>and to your point about IQ gains being temporary and that they become more similar with age, i would argue that this demonstrates that the environment can play a strong role in intelligence. it shouldn’t be a surprise that IQ gains made in the early years were temporary. after all, no one would expect the fitness benefits from an exercise regime to last a lifetime, so the same reasoning should be applied to the cognitive realm. it is noteworthy that IQ gains were achieved at all given the poor state of the education establishment. <br><br>lastly, i want to reiterate that i acknowledge a genetic component, but i don’t think that genetics explains why inner city kids leave high school reading at a third grade level.,(reply>), @Donald Taylor I appreciate the good faith response. Three things:<br>First, Richard stated (echoed by Murray/Herrnstein) that the identical twin studies provided different environments for each twin, but that when tested in adulthood, they had nearly identical IQs as their biological parents for both twins along with a host of other cognitive behaviors. M/H were only uncertain about the validity of a .20 correlation with the environment given lack of evidence supporting it.(head start failure, etc.)<br>Second, the same limitations to the impact of the environment exist for muscles, brains, or any biological function. You have to concede a genetic component to biology (unless you’re an extreme leftist).<br>Lastly, the psychometric data compiled over one hundred years is staggering in the area of cognitive testing, to deny it at this age is sad to say just denial of reality.,(reply>), A few things. First, The Bell Curve argued that the heritability of IQ is between 0.4 and 0.8, so you shouldn't have been convinced that it's practically all genetic. Secondly, at best what the twin literature shows is that IQ plays a role in IQ. it does not show that the environment is unimportant. heritability can only be measured while holding the environment constant. meaning that, given identical environments, there will be variations in IQ," and those differences will correspond to genetic variation. so far so good. the problem is that this only applies to identical environments. it tells you nothing about the effects of different environments on IQ. <br><br>To demonstrate why this is important", i would like to use an analogy. We know that muscle mass is highly heritable. However, that act in itself does not tell us anything about the effects of different environments on muscle mass. It only tells us that under identical conditions, there will be variation in muscle mass in a population, and it will be attributable to the genes. However, what if person A is physically active, and person B is a couch potato? Then, even though muscle mass is heritable, we can’t know if person A has more muscle mass than person B because of his genetics or because he is physically active. Moreover, if person C does pushups every night, and person D does heavy weightlifting, it complicates the analysis still. In this scenario, each environment has a drastically different effect on muscle mass," even though the heritability of muscle mass hasn’t changed. <br><br>In the previous scenario", we know how particular environments affect muscle mass because we have studied them. For instance, we know that light loads with high repetitions lead to muscular endurance, while heavy loads with low repetitions lead to muscular strength. We have even studied intermediate environments, that is, moderate loads with moderate repetitions, and we know that such environments are ideal for muscular hypertrophy. All that is to say that, we wouldn’t know any of that if physiologists were content with measuring the heritability of muscle mass. They actually went out and rigorously studied how different environments affected the trait in question. Likewise, intelligence researchers need to go out and rigorously study how different environments affect IQ, and only then will they be able to understand the variation in IQ across populations.