gwern comments on Information theory and FOOM - Less Wrong

6 Post author: PhilGoetz 14 October 2009 04:52PM

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Comment author: gwern 07 August 2011 04:30:05PM *  2 points [-]

In the first of several irresponsible assumptions I'm going to make, let's assume that the information evolved in time t is proportional to i = log(t), while the intelligence evolved is proportional to et = ee^i. I haven't done the math to support those particular functions; but I'm confident that they fit the data better than linear functions would.

This may be covered by the following assumption about 'spurts', but this doesn't seem to work for me.

If intelligence really could jump like that, shouldn't we expect to see that in humans already? For example, shouldn't we expect to see small mutations or genes with outsized effects on intelligence? Instead, we see that even a highly inbred population with many dozens of nasty genetic problems like the Ashkenazi only get 10 or 20 IQ points*, and we see a long-term stagnation in cranial capacity, and genetic surveys seem to (as far as I've heard) turn up hundreds or thousands of genetic variations weakly linked to small IQ increases. (I cover some related points in my article on evolution & drugs.) All of this makes intelligence look like it has a logarithmic relationship with diminishing returns.

* My understanding is that on a hypothetical 'absolute' scale of intelligence, as you get smarter, each IQ point corresponds to less and less 'actual' intelligence, due to the bell curve/relative ranking that IQ is - it's an ordinal scale, not a cardinal scale.

Comment author: gwern 09 August 2011 04:43:29PM 3 points [-]

hundreds or thousands of genetic variations weakly linked to small IQ increases

For example, I may be misinterpreting this new study http://www.guardian.co.uk/science/2011/aug/09/genetic-differences-intelligence but it seems to back me up:

"To test his idea, researchers looked at more than half a million locations in the genetic code of 3,511 unrelated adults. Each of these sites is where people are known to have single-letter variations in their DNA, called single nucleotide polymorphisms (SNPs). These variations were correlated with the individuals' performance in two types of psychometric tests that are established in assessing intelligence: one test measuring recalled knowledge (via vocabulary) and the second measuring problem-solving skills.

They found that 40% of the variation in knowledge (called "crystallised intelligence" by the researchers) and 51% of the variation in problem-solving skills ("fluid-type intelligence") between individuals could be accounted for by the differences in DNA. The results are published on Tuesday in the journal Molecular Psychiatry.

..."It is the first to show biologically and unequivocally that human intelligence is highly polygenic [involving lots of genes] and that purely genetic (SNP) information can be used to predict intelligence," Deary wrote in the journal paper.

Though the researchers now know the proportion of the variation in intelligence that is likely to be a result of genes, they do not know which genes are likely to be most important in determining intelligence. "If they can be found, and if we want to follow them up, to find out some of the mechanisms that underlie successful thinking, our best guess at present is that the number is huge. It could be many thousands," said Deary. "That could be a limitation to progress using this type of research."

From the abstract, "Genome-wide association studies establish that human intelligence is highly heritable and polygenic":

"General intelligence is an important human quantitative trait that accounts for much of the variation in diverse cognitive abilities. Individual differences in intelligence are strongly associated with many important life outcomes, including educational and occupational attainments, income, health and lifespan. Data from twin and family studies are consistent with a high heritability of intelligence, but this inference has been controversial. We conducted a genome-wide analysis of 3511 unrelated adults with data on 549 692 single nucleotide polymorphisms (SNPs) and detailed phenotypes on cognitive traits. We estimate that 40% of the variation in crystallized-type intelligence and 51% of the variation in fluid-type intelligence between individuals is accounted for by linkage disequilibrium between genotyped common SNP markers and unknown causal variants. These estimates provide lower bounds for the narrow-sense heritability of the traits. We partitioned genetic variation on individual chromosomes and found that, on average, longer chromosomes explain more variation. Finally, using just SNP data we predicted ~1% of the variance of crystallized and fluid cognitive phenotypes in an independent sample (P=0.009 and 0.028, respectively). Our results unequivocally confirm that a substantial proportion of individual differences in human intelligence is due to genetic variation, and are consistent with many genes of small effects underlying the additive genetic influences on intelligence."

Comment author: CarlShulman 09 August 2011 09:00:31PM 1 point [-]

Interesting. This study is a significant positive update for the feasibility of embryo selection for intelligence: it means that sufficiently enormous/high-powered GWAS studies can give good estimates of genetic potential for IQ in embryos. If common SNPs were less important relative to rare deleterious variants (in explaining heritability), then embryo selection would be complicated by the need to attribute effects to novel rare mutations (without having those properties made immediately clear by the population studies) based on physiological models.

Comment author: gwern 09 August 2011 09:52:34PM 1 point [-]

Well, it's good news if you didn't expect it to be possible at all (is that anyone here?), but it's bad news if you were expecting it to be easy or give high gains.

The result seems to say only that X percent of the genome was related in any way; when it comes time to actually predict intelligence, they only get '1% of the variance of crystallized and fluid cognitive phenotypes in an independent sample'. Given that they cover a lot of genetic information and that with this sort of thing, there seem to be diminishing returns, that suggests the final product will only be a few percent, and nowhere near the ceiling set by genetic influence. Maybe a few points is worthwhile but embryo selection is an expensive procedure...

Comment author: CarlShulman 09 August 2011 11:51:32PM 1 point [-]

We already knew that there weren't common variants of large effect. Conditioning on that, more heritability from common variants of small effect is better for embryo selection than heritability from rare variants.

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