raveneye

Well in order for intelligence to be “defined” by anything, it has to be defined. Since cognitive psychologists haven’t been able to come up with a definition that doesn't give at least a third of them a conniption (and not for lack of trying), I rather doubt that genes could do the job.

Perhaps you could give us a definition of “intelligence” in which variation in intelligence in any population is “almost completely” explained by genetics?

Not even performance on an IQ test is completely explained by genetics: heritability of this particular trait is anywhere from 30 to 80% depending on what study you want to believe, as sapiens pointed out.

And in any case, the heritability of test performance is irrelevant to the question of group differences, because the causes of within-group differences tell us absolutely nothing about the causes of between-group differences, in any trait. This is one of the most fundamental statistical truths about heritability, as pointed out by the originator of the concept, RA Fisher himself.

Intelligence is not even possible to measure. There is no yardstick. The concept itself is a cultural construct that varies from place to place and from time to time. We currently have an IQ test; a hundred years from now we might be attempting to test musical improvisational ability, or skill in real-time oral argument, or deftness at manipulating a person’s emotions, or talent in moving up a social hierarchy, or real-time situational problem solving, like the ability to survive a month in the Kalihari. None of these is even vaguely quantified by anything remotely resembling any IQ test. These tests are inherently circular anyway because they simultaneously define the construct in terms of the operation and the operation in terms of the construct.

Whatever test you claim shows that Group A has a higher intelligence than Group B, I guarantee I can construct a dozen different tests that show the exact opposite.

Or look at it from this angle: if a dentist can confidently pronounce the field of human evolutionary genetics “asinine” because it points out that there are no genetic races, then I think it’s time to throw up our hands and admit that the concept is irreducibly subjective.

Foolhardy? Since it’s impossible to even know why any particular person is more “intelligent” than any other particular person, going through life with an assumption of genetic equality can’t possibly hurt you in any way whatsoever.
I’d be more worried about drunk drivers, myself.

“Mongoloid” might narrow it down by a few percent, whereas knowing where a person’s parents were born narrows it down by about 80%. Numbers like that, by the way, are one of the values of scientific inquiry. They lead to conclusions like “the use of ethnicity alone will often be inadequate as a basis for medical treatment” (Manica, 2005).

Of course it is easy to “perceive”, that’s because people are compulsive classifiers, they can’t help it. Over the years we’ve seen the “Aryan race” the “German race” the “Jewish race” the “Italian race” the “French race” the “Irish race” the “English race” the “Scottish race” the “Puritan race” the “Hispanic race” the “black race” the “white race” the “red race” the “yellow race”, ….. you name it. Every culture and every generation has its own preferred list of races. In Brazil they “easily” recognize brancas, loras, morenas, mulatas, pretas, depending on subtle differences in the waviness of the hair, the width of the nose and lips, and the tint of the skin. You can have all 5 in one extended family. Hell you can probably have all 5 in one terribly confused person.

What any of this has to do with genetics, perhaps you can tell me, since “nothing is easier”?

And by the way, I see we now know the “value of scientific inquiry” for some folks: its value is to tell them what they already know. If it doesn’t, they simply toss it aside, call it “asinine,” and believe what they want.

Was that the answer you were shooting for in the OP?

Uh, those figures are correlations not heritabilities. Here’s the mean heritability calculated from these numbers: (0.86 - 0.57) x 2 = 0.58. However there is enormous spread in the correlations within each of Bouchard’s categories, so the mean doesn’t tell us much. If you take the spread into account, you get a range of calculated heritabilities from 0 to 1, which is the entire range possible. He, perhaps not surprisingly, didn’t point that out in his paper.

So in other words, your twin studies show a heritability muddling around somewhere in the middle, which is the same result as all the others.

And again, this is completely irrelevant to the subject of group differences in any trait whatsoever, let alone a trait that is inherently impossible to measure.

I agree with that, and would add that it helps to know how to calculate heritability.