That's a reasonable sort of question but would you say that MZ twins are treated differently enough to explain 40% of variation in earnings? If they were all l

That's a reasonable sort of question but would you say that MZ twins are treated differently enough to explain 40% of variation in earnings? If they were all locked in cellars out of shame I could see that being the case but that doesn't square with the identical twins I've known. But it actually is addressed by other studies such as adoption studies that show generally the same results. And, of course, there are potential problems with adoption studies too. But wouldn't it be suspicious if every[1] method of studying the problem we tried gives fairly close numbers but only because they all happen to be biased by the same amount in the same direction? [1]GWASes give lower numbers but we know that there are many sorts of genetic interaction they don't cover so this is expected.