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gwern comments on Why Are Individual IQ Differences OK? - Less Wrong
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It might be caused by a genetic change. Populations are becoming less inbred. This would be expected to raise IQs, though I don't know what the expected magnitude of change is.
It's been claimed ("Resolving the IQ paradox: Heterosis as a cause of the Flynn effect and other trends") that hybrid vigor/heterosis may help the Flynn effect, but this is not a popular explanation since it doesn't explain the pattern of gains on IQ tests or the apparent size of the Flynn effect. I mean, inbreeding depression alone costs much less than Flynn, so it's hard to imagine that outbreeding could be so valuable.
I suspect that my characteristics are partly due to hybrid vigor, as are my sister's. It's not so much "neg (inbreeding depression)" but more of a "when pooling both the strengths and weaknesses of two respective gene pools, the strengths of having access to more 'highly beneficial' genes tend to outweigh the weaknesses of being struck with 'detrimental genes' from a different region". So hybrid vigor isn't necessarily antisymmetrical (I doubt it is) to inbreeding depression. Beneficial/detrimental being relative to the current stage of human civilization in general, and your culture in particular, of course. Example: propensity for thalassemia, good once, bad now.
Interesting. Can you elaborate? What are the patterns exactly, and how do we know what inbreeding depression costs? From recent studies of inbred individuals? I'd be very surprised if it was the only cause of the gain in IQs, but as your reference says, it represents a pretty decent hypothesis for at least some of the effect.
Being confined to the subscales that look like pattern-matching and analogies, IIRC; I'm not sure which paper I get this from, but it seems Jensen does at least make this claim in http://www.charlesdarwinresearch.org/2010%20Editorial%20for%20Intelligence.pdf and in some citations in http://menghusblog.wordpress.com/2013/06/21/explanation-behind-the-non-g-gains-in-the-flynn-effect-introducing-the-measurement-invariance-model/ so there's some starting points at least.
Yes, that's how one would do it. The usual reference is to a study of Japanese cousin-marriages back in the '50s or so where IIRC the estimate was <5 IQ points, but there's been research since then, of course; a google for 'inbreeding depression intelligence' should bring some research to light.