novembro 14, 2019

About the "Bell Curve"

Simply stated, [Murray and Herrnstein’s argument] goes like this: If the variation in a particular individual trait is caused by genes, then the difference in average values of the trait in populations must also be caused by the genes. In the I.Q. debate, this argument takes the following form: variation in I.Q. among individuals in a population is caused (to a large extent, at least) by each individual’s genes. For group A, the average I.Q. score is higher than for group B. Hence members of group A must, on average, have higher I.Q. genes than members of group B.

However plausible this sounds initially, the fallacy of this logic becomes immediately obvious with a little thought and the use of a popular analogy. If we randomly take some corn seed and plant it in uniform, rich, well-tended soil, we will get a distribution of plant heights whose variation is caused by their genes. If we take a sample of seed from the same source and plant in poor soil, we will again get a variation of heights that is caused by the genes. But the second group will have a lower average height than the first, even though the plants come from the same gene pool. This difference in average values is caused by the environment and not the genes, a fact known to every farmer.

So it is possible to have a variation that is purely genetic in some trait within a single group, while the difference in average values of the same trait between different groups is caused purely by environment. For example, the variation in individual heights has a substantial genetic component. But in Japan, which has been a relatively isolated country, average heights have risen considerably since World War II, a fact easily explainable by better nutrition.

https://freethoughtblogs.com/singham/2018/04/03/the-drearily-predictable-resurgence-of-the-race-and-iq-debate/

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