“So, please do enlighten us. What would be the expected I.Q. of the offspring in this instance (one parent with an I.Q. of 80, the other with an I.Q. of 100)?
Please give us your estimate!”
Using the narrow-sense heritability of IQ and regression to the mean, let’s look at this. 100 is the population mean, so the couple deviates by -10 points. Ti calculate the child’s iq
Expected Child IQ = Population Average + H x ({Mid-Parent IQ - Population Average)
Where H is heritability and is generally in the range of 0.5 to 0.6 meaning 50% to 60% of the variation in IQ in a population is due to additive genetic effects
So we get 94 as the statistical expectation.
But remember that Parents pass on a random half of their genes. A child could luckily inherit the top-performing gene variants from both parents, or unluckily inherit the lower-performing variants. This creates a wide bell curve of possibility around that 94 average for individual siblings.
Kinda like “Young Sheldon “
But I still hold that we cannot discount culture and other environmental factors.
That is why public schools should be stricter and the syllabus and discipline at 1930s level. No separate leniency for black students for instance.
for decades, well-meaning people have tried to close this gap or that. Throwing money down the toilet, trillions. This program and that. This legislation or that. After decades, the gaps stay miraculously gapped. After a while you just have to accept nature.
People just aren’t equal. We are different and that’s just life. You just can’t have equal outcomes. Don’t beat yourself up.
Thanks for your analysis! But I deliberately wanted to exclude the cultural / environmental factors! I was interested purely in the genetic component.
Your answer ("I.Q. of 94") is, indeed, sensible!
I suppose that one could formulate the explanation as follows: The child's I.Q. would not be the pure mathematical average of "90" because the parents - despite having (supposedly) well-defined I.Q.s of "80" and "100," respectively - are derived from the same wider population, which displays a distribution peaking at "100." If instead we took two other parents - the mother from a long-established and hence stable population of 80s (i.e., where the Gaussian curve peaks at 80), and the father from an equally stable population of 100s - then the offspring would have an I.Q. of 90.
But since, in reality (or, at least, in this thought experiment), the two parents come from the same basic "stock," we would expect (besides the mere mathematical average) the "regression towards the mean" to take effect.
Right? (You obviously have more competency in this field than I.)
But if we took two individuals from entirely separate gene pools (as far as that is possible in the human species), the "regression to the mean" would have less effect, richtig?
Regards,