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In my mind, the bigger issue with twin studies trying to show that (say) IQ is highly genetic is that humans do not reproduce by cloning. And regression toward
by bell-cot 11mo ago
In my mind, the bigger issue with twin studies trying to show that (say) IQ is highly genetic is that humans do not reproduce by cloning. And regression toward the mean is very much a thing for heritable traits.
In other words - Junior should not be presumed to be smarter, fitter, more deserving, or destined for success, just because his parents did well. No matter how attractive that conclusion might sound, to people who consider themselves to be the "better" sort.
- DaveZale 11mo agoiq is "polygenetic" with the consensus estimates at 50-80% based on genes success has components of luck as in "right place, right time" for someone with the right qualities and connections, and many of the very successful are quick to admit this I am a 3rd generation machinist along the paternal line, and although the machines I operate are in expensive labs, those my father and grandfather operated were probably just as challenging. Engineering also seems to often run in the family. How much is nature and nuture? "It varies" is a safe response
- tptacek 11mo agoWhoah, no, there is definitely not a consensus for 50-80%, and most of what's being published now refutes the 80% end of that range --- the 80% estimates come from underpowered studies like MISTRA that improperly assumed independent environments for twins reared apart.
- DaveZale 11mo agookay, I saw the paper saying 500 genes are involved. So does a single number for iq mean anything? Does the number depend upon what is tested?
- tptacek 11mo agoWe have essentially no mechanistic understanding of gene/intelligence interactions. Rather, we have cohorts of people tagged with traits (educational achievement, tested IQ, height, etc), all sequenced, and then we can run correlation surveys across all their genomes to identify correlations between alleles and traits. When you do that, you get 10-30% heritability numbers; the gap between that and the range for MZ/DZ twin studies (the 50-80% you often see) is "the missing heritability problem".
- DaveZale 11mo agodoes epigenetics play a significant role? Within one lifetime or several generations?
- tptacek 11mo agoWay above my pay grade. Probably! Or probably not?
- red75prime 11mo agoRegarding missing heritability: https://www.astralcodexten.com/p/the-good-news-is-that-one-side-has https://www.astralcodexten.com/p/the-good-news-is-that-one-s... "That is, once you include the rare variants, the amount of genetic variation that “should” exist but doesn’t shrinks to only 12%. Plausibly an even bigger study, investigating even rarer variants, could shrink the gap further, all the way to zero." Of course, even then heritability will not be 100%.
- tptacek 11mo agoI don't think the rare-variant hypothesis is taken seriously anymore by practitioners, but feel free to cite.
- deleted 11mo ago[deleted]
- dragonwriter 11mo agoThat doesn't sound like a problem with twin studies exploring the degree to which IQ is genetic, that sounds like a problem with people treating aggregate tendencies and associations as a basis for individual discrimination.
- bell-cot 11mo agoYes-ish. Hence my use of "issue". The problem is most people's zealous desire to read socially self-serving conclusions into any data they can find on such subjects. And when they really like the Q.E.D. punchline, humans have very low standards for the "logic" used to reach it.
- ionwake 11mo ago"most people's zealous desire to read socially self-serving conclusions into any data they can find" what planet are you living on? also your comment was completely incorrect and missing the entire point of twin studies.