West Germany and East Germany, North Korea and South Korea, China and Taiwan These nations exhibit a strong difference in adult height also. The reason is well

West Germany and East Germany, North Korea and South Korea, China and Taiwan These nations exhibit a strong difference in adult height also. The reason is well known to be mass childhood malnutrition in command political-economies. Ethical studies cannot reproduce the effect because malnourishing children is not ethical. Relationships between environment and heritable factors in human development are heavily dependent on context and cannot be objective by definition. When that context includes an overwhelming factor like childhood malnutrition or childhood lead exposure, the results will be extreme. The usual randomized controlled trials or twin studies or genetic marker studies cannot adequately deal with that kind of effect and are not really intended to. Modern academic studies of IQ seem to refer to populations of well fed, healthy, well cared-for, children raised with free education according to a uniform curriculum in free liberal nations. That is very much a formula for shrinking environmental effects by shrinking environmental variance. It's the reverse of a twin study; you make the environment uniform so all the difference in outcome must be a result of heritable factors. Such studies often indicate that g is 60% heritable. If you threw in some lead poisoning -- as was near universal in the 1950-1975 generation -- or childhood malnutrition -- very common before the twentieth century everywhere -- you would get a very different result. That's not a defect; it's built into the nature of these studies.