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AM: I'm having a hard time believing the average IQ is rising. I'm not saying you are wrong. I'm just saying that I don't see much evidence of it.

I know -- I get the same impression. Over the years I have thought a lot about this, and I think I know what is going on.

1. Our view of what life was like in previous centuries is seriously off base. Most people were employed in agriculture, seldom completed more than a few years of school, did not more around much, and lived on isolated farms. They did not write about their experiences. Their lives and struggles are largely lost and forgotten, except for a small number of diaries that have survived. By modern standards they were malnourished, suffered critical vitamin deficiencies, did not receive mental stimulation at a young age, suffered high rates of physical illnesses and injury, and were often badly and chronically abused.

2. Our view of what life is like now is also seriously off base. Most middle-class college-educated people associate only with each other, and seldom interact in any meaningful way with others. This gives us a very distorted picture of the full range of human experience. In IQ terms: most people with an advanced degree have an IQ of perhaps 120, and seldom interact socially with anyone under 100. Yet fully 50% of the population has an IQ that is below 100. If we think of the 100+ population as "normal", then we have a radically wrong image of the true variation in the population.

3. Almost all improvements in IQ have come at the low end, in the form of reductions in mental retardation. This conclusion comes from many studies. In truth we have made *huge* advancements in the prevention of mental retardation over the past century, and it shows in the distribution of intelligence scores. Most of the improvements have come in eliminating or reducing diseases and conditions which cause mental retardation. Some standouts: the removal of lead from paint and gasoline probably raised the average IQ of North America by six points, mostly at the low end of the scale. Reducing the impact of infectious diseases may have accounted for ten points, spread out over a full century. Better nutrition, especially vitamins and critical minerals, may have been even more important -- again, mostly at the low end of the scale. There are several studies that claim to have shown that *no* improvements at all occurred at the high end of the IQ scale.

4. None of these improvements have anything to do with genetics. Every bit is a result of better conditions, better nutrition, fewer diseases, more education, less abuse, better medications, and a much better environment.

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