wjb3IQ differences of identical twins reared apart are influenced by education
https://www.sciencedirect.com/science/article/pii/S0001691825003853
An interesting tidbit in the nature vs. nurture debate is that nature and nurture interplay in ways you might not expect. For instance, height is approximately 90% heritable in the United States -- but this does not mean that in a vacuum height is mostly genetic. It means that in the United States nutrition has mostly been solved (and yes, even the "food insecure" in the US rarely lack for the actual calories which would impact their height -- food insecurity causes other problems) and therefore the only real differences that can remain are the genetic differences.
It might be useful to look at any twin study through this lens; if we know for sure the genes are the same and nature is off the table, how much variance remains?
> It means that in the United States nutrition has mostly been solved
Nature is not off of the table. We've just traded problems with calorie quantity to quality.
condition US prevalence
hypertension 49%
obesity 40%
metabolic syndrome 40%
prediabetes 38%
fatty liver disease 25%
diabetes 16%
coronary disease 5%
That's not mostly solved, that's tens of millions of truncated, immiserated lives. Of course calorie quality differences are important to child development.
I think you'll find in comparisons of 2025 to the turn of the 20th century that we lives are, by comparison, neither truncated nor immiserated. Anyways, this has nothing to do with the topic of the thread.
My argument is that we cannot simply say, they're both getting enough calories, therefore we can discount the nutritional component of their IQ differences. Sufficient calories do not remove nutrition as a confound.
You're handwaving away the nutrition hypothesis for the Flynn Effect, and I think losing sight of the timeline for the comparison. It's going to be very difficult to make any case like this if we're looking back to 1900, which is what we're doing when we talk about the nutrition/intelligence shifts we see in stats.
We seem to be having different conversations. I'm responding to
if we know for sure the genes are the same and nature is off the table, how much variance remains?
... and saying that nature isn't off the table at all. Are you saying that it is?
For intelligence? Where "nature" refers to "innateness" of the trait? I think it mostly is off the table, yes. I'm not saying that the only or even the most important environmental trait is nutrition.
(I think it can't possibly be entirely off the table, since we have mechanistic understanding of some gene-mediated cognitive disabilities).