>>13385402>regression to the meanIt doesn't exist. It's just made up. The genetic portion of children's intelligence is random depending on the genes available in their parents. Often children can have higher IQ than both of their parents. Sometimes they have lower IQs. However, the distribution will fall on a bell curve depending on population averages or what genes are in each parent.
>average IQ intermediate between two groupsThis is a matter of statistics given that two different groups have different average IQs as determined by genes. If you have a person from a group with average IQ 100 and one from a group with average IQ 70 and they have children, half of the genes come from the 100 IQ and half come from the 70 IQ. Given the same standard deviations between their populations, you expect the children to have an intermediate IQ of 85.
For example, take two four sided die (2d4) and roll them and add the numbers together, and, take two six sided die (2d6) and roll them. The average roll for 3d4 is 5. The average roll for the 2d6 is 7. This example is even more extreme as there are different standard deviations. Now take one die from each pair. Roll them together, we have values
x; 1d4 + 1d6 (events)
2; 1 + 1 (1)
3; 1+ 2, 2+1 (2)
4; 1+ 3, 2+2, 3+1 (3)
5; 1+ 4, 2 + 3, 3 + 2, 4+1 (4)
6; 1 + 5, 2 + 4, 3 + 3, 4+2, (4)
7; 1 + 6, 2 + 5, 3 + 4, 4 + 3 (4)
8; 2 + 6, 3 + 5, 4 + 4 (3)
9; 3 + 6, 4 + 5 (2)
10; 4 + 6 (1)
Average roll is 6. Here we see that the average is intermediate. If we took 2d4 and 2(d4+2) (same distribution, one is just shifted to the right by 2), the average of 2d4 is still 5 and the average of 2(d4+2) is 9. But the average for 1d4 + (1d4+2) = 2d4+2 is 7, the intermediate value between the two averages. It works the same way with gene combinations for IQ as well as other traits, height, foot size, etc.
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