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I think the scientific implications include a chance at a better understanding of the physical basis of intelligence, and hopefully ways of increasing intelligence.
Finding the genetic causation of intelligence would be fantastic.
HBD isn't the idea that there's genetic causation of intelligence, however; it's the idea that the genetic causation factors vary in frequency between population groups (namely, races), and specifically, that certain population groups have lower intelligence as a result in the variance of frequency. To which I must respond that, while it should surprise us if those genetic causation factors don't vary in frequency across population groups, it should also surprise us if the frequency distribution of given genetic factors consistently advantages or disadvantages a single population group. (That is, there should be genetic causal factors which improve intelligence that are more common in black people, as well.)
Which is to say, HBD, as a proper idea rather than racism, suggests we should be mixing races to get the best genetics from every group. Given, as I understand it, that the greatest variance in genetics tends to be in African people, the ideal is probably closer to the African cluster (being larger and thus having more potential for positive factors) than the European cluster.
But that isn't the position HBD advocates generally take, to put it mildly.
No. Think about a random walk on a 1D line, or about generating a normal based on the sum of a lot of random variates. If you do 2 random walks A and B, do you think that A and B will wind up in the exact same position because 'there should be steps which increase the position in B as well'? Or, 'A and B should sum to the same, because B will have some variables which were higher than in A'? In expectation, A and B may have the same average value, and may asymptotically converge given enough steps or variates summed but in any particular realization, with a fixed number of steps of summed variates, they can and probably will be quite far apart. Genetic drift is a considerable force, and more still if you invoke any kind of different selection pressures (such as, say, for other expensive phenotyptic traits like infection resistance at the expense of highly expensive brain development).
I disagree. This may not be the position that racists take, but HBDers often suggest outbreeding & hybrid vigor as good things and from Jensen onward have emphasized the problematic effects of inbreeding depression & homozygosity. Razib & Jayman practice it, and HBD Chick, Cochran also come to mind as bringing up these issues fairly regularly, I think Chuck probably has too. More historically, I believe this was one of the disputed topics among early eugenicists; for example, Razib gives a quote from R.A. Fisher from page 238 of The Genetical Theory of Natural Selection:
So I'm surprised you have this impression.
There are, last I checked, at least 100 genetic markers associated with intelligence. And convergence, short of genetic drift/selection pressures, should be expected; while it's possible for there to be a difference, given the law of large numbers, we should expect the distribution to be pretty similar.
Selection pressures like plagues that wiped out the majority of the population on more than one occasion?
Why are you surprised?
Many more actually, the upcoming SSGAC paper alone reportedly identifies 80+ hits but even that paper's full polygenic score only explains about a third to a fifth of SNP contributions, so there's going to be many more hits to come and probably thousands of non-zero variants beyond that. But it doesn't make a difference because both group and individual differences are based on the same set. Individual differences arise from very small net differences (due to the CLT), and so you only need small changes in allele frequencies to also produce group differences on the order of individual differences. Take a look at my calculations and simulations in http://www.gwern.net/Embryo%20selection#limits-to-iterated-selection making concrete the issue of how much absolute genetic difference translates to observed relative differences; it's not much, and it would take a very small average difference to produce group differences like we see. Or look at the scale of Piffer's polygenic scores. Also consider 'soft sweeps'.
(I was looking into this because it has some important implications: the small variance means that embryo selection is going to be weak since you don't get embryos with large differences in their polygenic scores, but it also means that there is an enormous amount of potential improvement you could make with direct embryo editing. If the genetics of intelligence were just 50 genes or something small like that, selection would be more profitable since the sum of 50 random binomials is much more spread out than 10,000, but it also means that once you've edited all 50, you've 'run out' of genes to tweak and have topped out at a relatively few SDs of relative intelligence improvement. But with 10,000, you have so many knobs to tweak that you can go straight to whatever the neurophysiological limit of a human brain is.)
'Majority'? I don't think even the Black Plague killed a majority of the European population, if that's what you mean. And no. Only a few occasions doesn't create much of a selection pressure, compared to constant disease and parasite load over deca-millennia. Try the breeder's equation on the impact of a few dozen selection events killing 1/3 of the population versus say 10,000 selection events killing 10% of the population.
'Pretty similar' is not nearly enough, and again, you can't neglect genetic drift and selection pressures. It's a fact that human populations do not experience significant gene flow and so genetic drift will be operating.
Because if you're going to claim that HBD is irrelevant and futile and has no policy or real-world implications, I assume you must have been reading extensively about HBD to understand all the threads that go into it, which will lead you to those writers frequently.
Not quite. You are thinking of breeding people to develop a trait (in this case, intelligence) and are correct that you want diversity in your breeding stock. However what that diversity gets you is not just top-end results. It gets you variance -- basically, you'll get a few geniuses and a lot of idiots.
In animal breeding that's not a issue -- you kill off (or prevent from breeding) all the failures and just keep the very few top results. For humans that would be... problematic.
So if you encourage greater variance in outcomes and you keep all of them, the question becomes who breeds faster: idiots or geniuses. Let me point out that I'm not optimistic about that question.
By the way, empirically people with both black and white ancestry have average IQs between the pure blacks and the pure whites. This seems to indicate that you don't get much by cross-breeding.
Sometimes animal breeders find that two different breeds nick meaning their offspring consistently have more desirable traits than either of their parents do. To the best of my knowledge, this hasn't been observed in humans but then again I don't know if anyone has really investigated the possibility.
Not quite. It depends on who the mother is, and who the father is.
But I'm suggesting something slightly different: To the extent we engage in eugenics to improve our genetic lineage, we should be pulling genetics from every stock.
But we don't and are not very likely to start in the near future.
Genetic modification isn't that far away, and in some respects with regard to some conditions genetic culling of reproductive cells is already here. Both are forms of eugenics.
Direct genetic modification CRISPR-style doesn't require any cross-breeding, you just insert the genes you like and delete the ones you dislike.
In any case, this has little to do with the usefulness of HBD claims.
My impression is that breeding from diverse backgrounds gets you hardiness-- mutts are less likely to have the specific genetic ailments you get from purebreds. On the other hand, you're less likely to get extraordinary development of particular traits.
On what is possibly the gripping hand, that's dogs who've been selectively bred, which is not the same as people roughly adapted to different environments.
Yes, but I think this works on a different scale. Purebred domestic animals are usually heavily inbred, precisely to push a particular trait to new heights. In the standard textbook manner this makes the chances of the animal getting multiple copies of some recessive gene skyrocket, thus the fragility.
The human equivalent is marrying your cousins (inbred human populations exist, they usually don't look too good) which is different (scale) than marrying someone from a large enough gene pool (e.g. like all Europeans).
Now that you mention it, I haven't heard of research on people who have the most varied ancestry.