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And your claim “ If an individual with an IQ of 100 has a child with an individual with an IQ of 80, the child will statistically have an IQ of 90, creating a downward trend” That is NOT how IQ works. Because intelligence is heavily influenced by environmental factors and complex genetic combinations, children of parents with extreme traits (either exceptionally high or exceptionally low IQs) statistically tend to move back toward the population average (100), rather than splitting the difference precisely or continuing a downward trend.

Regression toward the mean. Yes.

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!

My guess? The offspring would have an I.Q. of 90.

Without factoring in environmental influences, etc. - which we can't know in this hypothetical.

Regards,

“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.

Yes, regression to the mean is a factor. Due to environmental variance (as well as non-additive genetic effects, such as dominance and epistatic effect), the IQ of a 100 x 80 cross would probably be somewhat higher than 90, but still below 100. Nevertheless Rando’s point stands - if you cross-breed bright and dull people, their children are expected to be duller than the better parent.