That 50% number keeps coming up, this time in a Nature article "Genomic analysis of family data reveals additional genetic effects on intelligence and personality." Two things to note: this doesn't mean that the other 50% is environmental. To date, very little can be shown to be environmental with the strength that this study shows for genetics. The remaining 50% is "other," and seems to be uncomfortably random. A Tom Stoppard world.
The second point to be alert to is that personality characteristics are being measured with more rigor and confidence, and these will increasingly enter the discussion of heritability
(HT: Steve Sailer)
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I'm a bit fuzzy on the distinction you're drawing between genetics and heredity.
Acch! Fixed. Thanks.
And fixed again. What was I saying about IQ?
Gotcha now. I did notice in the summary that (as I understood it) the effects of genetics attenuate as you get farther from direct family connections. I first thought it was a reference to that.
That would be much too complicated for me. I used to be intelligent enough for such subtlety, but now I'm just coasting.
I can offer a suggestion for the non-genetic/non-environmental differences. In my work we see a lot of brain MRI and CT scans. The radiologists often note physical differences in circulation that are far from the textbook norm. Arteries running where arteries don't normally run, or lacking, or one branch being much smaller or larger than the norm. All, apparently, normal variation of unknown origin. When the basic body plan is laid down in the fetus, a lot of chance is involved.
The second thing is that reductions in blood flow reduce alertness. The docs will go in and ream out or balloon a blocked artery, and if all goes right the patient regains a lot of mental acuity. A pre and post IQ test would I expect show a big jump after a successful proceedure.
My point being that whether you are born with good blood flow or not is largely chance. It isn't environment or genetics. It's just chaos in those first few weeks after conception when the basic body tracts are laid down.
@ Tom - that is an excellent example of exactly what I meant. Thanks.
More broadly, we tend to think of "environmental" as "the stuff that we can change". But something like influence from the prenatal environment is environmental—in the sense that it's not genetic—but it can't be changed after birth. We should be careful about thinking genetic/non-genetic equates to "stuff we don't control/stuff we control".
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