David Deutsch: evaluation

Transcript context

…So there are differences in the brain level that correlate with IQ, right? So your actual skull size is like a 0.3 correlation with IQ. There are a few more like this. They don't explain the entire variance in human intelligence or the entire genetic variance of human intelligence. But we have identified a few actual hardware differences that correlate. Suppose that on the contrary, the results of these experiments had been different. Suppose that the result was that people who are brought up in the same family differ only in the amount of hair they have, or in their appearance in any other way, none of those differences made any difference to their IQ. Only who their parents were made a difference. Wouldn't it be surprising that there's nothing else correlated with IQ other than who your parents are? Now, how much correlation should we expect? There are correlations everywhere, and they're these things on the internet: jokes, memes, or whatever you call them. But they make a serious point where they correlate things like how many adventure movies have been made in a given year correlated with the GNP per capita. That's a bad example because there's an obvious relation, but you know what I mean. It's the number of films made by a particular actor against the number of bird flu outbreaks. Part of being surprised by randomness is the fact that correlations are everywhere. It's not just that correlation isn't causation. It's that correlations are everywhere. It's not a rare event to get a correlation between two things. The more you ask about, the more you will get correlations. What is surprising is that the things that are correlated are things that you expect to be correlated and measured. For example, when they do these twin studies and measure IQ, they control for certain things. Like you said, identical twins reared together—they've got to be reared together. But, there are infinitely more things that they don't control. So it could be that the real determinant of IQ is, for example, how well a child is treated between the ages of three and a half and four and a half. Where “well” is defined by something that we don't know yet. Then, you would expect that thing we don't know about, and nobody has bothered to control for it to be correlated with IQ. But unfortunately, that thing is also correlated with whether someone's an identical twin or not. So it's not that it’s identical twins that are causing the similarity. It's this other thing. This is an aspect of appearance or something. If you were to surgically change a person, and you knew what this thing was, you would be able to have the same effect as making an identical twin. Right. But, as you say, in science, or to explain any phenomenon, there's an infinite amount of possible explanations, right? You have to pick the best one. So it could be that there's some unknown trait, which is so obvious to different adoptive parents, so they can use it as a basis for discrimination or for different treatment.…

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