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Small-Scale Question Sunday for May 7, 2023

Do you have a dumb question that you're kind of embarrassed to ask in the main thread? Is there something you're just not sure about?

This is your opportunity to ask questions. No question too simple or too silly.

Culture war topics are accepted, and proposals for a better intro post are appreciated.

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I realise this may come across as stirring the pot, but I hope I've been here long enough to have earned the benefit of the doubt.

In the context of the HBD debate, could someone please ELI5:

  • The concept of heritability and how it relates or doesn't relate to genetic causes of individual or group differences. I am aware of the "books at home" example. Is that all there is to it?

  • What precisely g is?

  • Steelman(!) Turkheimer's position. No, I don't want to hear about his politics.

  • Roughly summarise the position of Kirkegaard et al.

This whole debate always gets technical so quickly that I very often just get lost. I don't want to rehash the arguments here, I would like to understand the basics. But the waters are often so damn muddied (purposely so, I suspect) that it's very hard to get a grasp of what people are even fighting about.

"Books at home" is presumably shorthand for a wide range of parenting practices, and indeed I would bet that it originated as a relatively easily measured proxy for parenting practices.

Btw the graph from here happened to be going around today; it shows a large gap in cognitive skills between identical and fraternal twins, but also a substantial gap between siblings raised together and siblings raised apart. (Note that some small pct of the difference between identical and fraternal twins might conceivably be caused by parenting, since at least in the past parents often tended to treat identical twins identically-- dressing them the same, etc -- which might also manifest itself in forcing both to experience some of the same experiences (eg, if one wanted to take violin lessons, both had to). Again, I would guess that would have a very small effect even if true, but of course that is a guess).

Also, one consideration that I never see mentioned in popular discussion of HBD is potential congenital, but not genetic, causes. Eg if poor people have dumber kids than other people, is it all either genetics or upbringing? Or is some the result of greater propensity for drinking, drug use, poor diet, etc during pregnancy?

Also, one consideration that I never see mentioned in popular discussion of HBD is potential congenital, but not genetic, causes. Eg if poor people have dumber kids than other people, is it all either genetics or upbringing? Or is some the result of greater propensity for drinking, drug use, poor diet, etc during pregnancy?

How is it possible you never saw it mentioned? Twin adoption studies specifically rule out these sorts of issues.

No, they don't. They rule out an argument that some part of the variation between identical twins raised together and apart is caused by the environment in the womb. But it does not rule out an argument that some part of the difference between identical twins born to a poor woman and identical twins born to a middle class person is caused by the environment in the womb.

They do rule out the argument that the variation between groups of identical twins of the same socio-economic class is caused by the environment in the womb, though.

Only if the correlation between identical twins of class X is identical to the correlation between identical twins of class Y. Is that what studies show? Because I know in other contexts the effect of genetics is mediated by socioeconomic status.

They don't need to be identical. The genetic correlation just has to be bigger than the SES correlation within a given SES group. Or you can just look at kids born to rich families but who got adopted out to parents of various classes.

It was my impression that this is what the studies, in fact, show. Maybe an earnest full-HBDer can give a link, I'm just a reluctant and partial one, that prefers the whole thing to be proven false.

They don't need to be identical. The genetic correlation just has to be bigger than the SES correlation within a given SES group

I don’t know what you mean by the SES correlation within a given SES group. Within each SES group, every kid is coded with the same SES. There is no variation in SES to use to calculate correlation, is there?

Regardless, if there is a difference between the pct of variation explained by genetics in twins born to low SES mothers and the pct of variation explained by genetics in twins born to high SES mothers, then that difference is caused by something, right? That is true even if the genetic correlation is enormous.

Or you can just look at kids born to rich families but who got adopted out to parents of various classes

Yes, but my question is whether such studies have ever been done.

I don’t know what you mean by the SES correlation within a given SES group. Within each SES group, every kid is coded with the same SES. There is no variation in SES to use to calculate correlation, is there?

There's still some income variation within a group, no?

Regardless, if there is a difference between the pct of variation explained by genetics in twins born to low SES mothers and the pct of variation explained by genetics in twins born to high SES mothers, then that difference is caused by something, right? That is true even if the genetic correlation is enormous.

Yes, but if the genetic correlation significant (doesn't even have to be enourmous) that already requires us to overhaul the way we talk about social issues. If you want to focus on the environmental things we can do to improve outcomes for people, go right ahead, but you can't presume isms because groups have different outcomes.

Yes, but my question is whether such studies have ever been done.

Once again, I believe so, but it would require digging through ages old SSC / TheMotte posts, or the materials of Kirkegaard / Sailer / Murray. I'm inclined to do neither, as I wish we could bury the whole idea.

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