New study on genetics of inteligence

[Heraclitus]

Comment on the study by Charles Murray

A landmark article went online a few days ago in the journal Molecular Psychiatry. The study was prepared by a team of 32 researchers headed by the University of Edinburgh’s Gail Davies and entitled “Genome-wide association studies establish that human intelligence is highly heritable and polygenic.” The study’s methods do not lend themselves to easy explanation unless you’re at home with SNPs (single nucleotide polymorphisms) and inverse variance weighted models used to capture “the variance in the trait that is due to linkage disequilibrium between genotyped SNPs and unknown causal variants.” But the bottom line of the article is reasonably simple. Using nothing but genetic information, the team of researchers was able to establish that the narrow heritability of crystallized intelligence (the kind that can be more easily affected by education) is at least 40 percent. The narrow heritability of fluid intelligence (the kind that involves pure problem-solving ability, independently of acquired knowledge) is at least 51 percent. Note the at least. The study’s authors explicitly state that these estimates are lower bounds.

Shelves of books and articles denying or minimizing the heritability of IQ have suddenly become obsolete. Those who continue to claim that IQ tests don’t measure anything real inside the brain also have their work cut out for them.

The study itself:

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.

[KrazyHorse]

These are similar numbers to those reported in twin studies and even in simple regressions...

[Heraclitus]

I would be surprised if it where otherwise.

[Uncle Sparky]

Gee... somewhere between 40%-5?% likelihood of something being accurate. I'll let you call it - heads or tails?

[giblets]

Gee... somewhere between 40%-5?% likelihood of something being accurate. I'll let you call it - heads or tails?

I'm not sure how you came up with "40-50% likelihood of something being accurate".

[Heraclitus]

These are similar numbers to those reported in twin studies and even in simple regressions...

It just dawned on me that you might not realize why this study does tell us something new. It undermines Flynn and Dickens’ often cited model of IQ, according to which differences within and between population are quite malleable. As Flynn explains, the model is based on the idea that high heritability estimates are an illusionary product of kinship studies. Accordingly, the high estimates reflect undetected gene-environment correlations, not large genetic differences.

Flynn(2008):

Seven years ago, William Dickens of the Brookings Institution, decided to do some modeling of his own and asked my help in applying it to real-world situations (Dickens & Flynn, 2001a; 2001b). We believe that it solves the identical twins paradox without positing a Factor X. It makes an assumption that may seem commonplace but which has profound implications, namely: that those who have an advantage for a particular trait will become matched with superior environments for that trait.

Recall studies of identical twins separated at birth and reared by different families. When they grow up, they are very similar and this is supposed to be due solely to the fact that they have identical genes. But for that to be true, they must not be atypically similar in environment, indeed, the assumption is that they have no more environment in common than randomly selected individuals. To show how unlikely this is, let us look at the life history of a pair of identical twins.

John and Joe are separated at birth. Both live in an area (a place like the state of Indiana) that is basketball-mad. Their identical genes make them both taller and quicker than average to the same degree. John goes to school in one city, plays basketball a bit better on the playground, enjoys it more, practices more than most, catches the eye of the grade-school coach, plays on a team, goes on to play in high school where he gets really professional coaching. Joe goes to school in a city a hundred miles away. However, precisely because his genes are identical to Joe’s, precisely because his is taller and quicker than average to exactly the same degree, he is likely to have a very similar life history. After all, this is an area in which no talent for basketball is likely to go unnoticed.

On the other hand, Mark and Allen have identical genes that make them both a bit shorter and stodgier than average. They too are separated and go to different schools. However, they too have similar basketball life histories except in their case, both play very little, develop few skills, and become mainly spectators.

In other words, genetic advantages that may have been quite modest at birth have a huge effect on eventual basketball skills by getting matched with better environments — and genes thereby get credit for the potency of powerful environmental factors, such as more practice, team play, professional coaching. It is not difficult to apply the analogy to IQ. One child is born with a slightly better brain than another. Which of them will tend to like school, be encouraged, start haunting the library, get into top stream classes, attend university? And if that child has a separated identical twin that has much the same academic history, what will account for their similar adult IQs? Not identical genes alone — the ability of those identical genes to co-opt environments of similar quality will be the missing piece of the puzzle.

Note that genes have profited from seizing control of a powerful instrument that multiplies causal potency, namely, feedback loops that operate between performance and its environment. A gene-caused performance advantage causes a more-homework-done environment, the latter magnifies the academic performance advantage, which upgrades the environment further by entry into a top stream, which magnifies the performance advantage once again, which gets access to a good-university environment. Since these feedback loops so much influence the fate of individuals throughout their life-histories, the Dickens/Flynn model calls them “individual multipliers”.

Understanding how genes gain dominance over environment in kinship studies provides the key to how environment emerges with huge potency between generations. There must be persistent environmental factors that bridge the generations; and those factors must seize control of a powerful instrument that multiplies their causal potency.

The recent findings make a strong version of this model untenable. As the authors of the study note, the findings unquestionably establish a large additive genetic component to (within population) IQ differences.

[Berzerker]

I dont understand, but my daddy and mommy would have

[SlowwHand]

"Intelligence" in your thread title isn't spelled correctly.

[Zoetstofzoetje]

duh

[KrazyHorse]

It just dawned on me that you might not realize why this study does tell us something new. It undermines Flynn and Dickens’ often cited model of IQ, according to which differences within and between population are quite malleable. As Flynn explains, the model is based on the idea that high heritability estimates are an illusionary product of kinship studies. Accordingly, the high estimates reflect undetected gene-environment correlations, not large genetic differences.

I don't follow this literature as closely as you do, so I have no idea how much impact this hypothesis has had on recent research, but it appears laughable on its face. As a relatively-informed outsider, I had long ago come to the conclusion that intelligence as measured by IQ had around a 50% genetic component.

[Zoetstofzoetje]

if i remember correctly, there´s the two traditional camps duking it out: nature and nurture. the nature guys say that talent is innate, and the nurture guys say that it´s comes with experience. in the first camp you´ll find the standard autistic positivist. the second camp is populated by treehugging socialists. then there´s the minority who say that it´s a bit of both, but they´re shunned by the powers that be (the professors that became famous by advocating either extreme).

[Sir Og]

I don't follow this literature as closely as you do, so I have no idea how much impact this hypothesis has had on recent research, but it appears laughable on its face. As a relatively-informed outsider, I had long ago come to the conclusion that intelligence as measured by IQ had around a 50% genetic component.

How have you reached that conclusion? Have you compared people with identical genes and different enviroments?

[Aeson]

Kids seem pretty dumb when they're babies. So I can see how only 50% of their intelligence is inborn. The rest they gotta learn like the rest of us did

(I am confused about where the black admixture is in this study though...)

[Heraclitus]

"Intelligence" in your thread title isn't spelled correctly.

Curse my Slovenian upbringing! Or rather English spelling.

[Heraclitus]

(I am confused about where the black admixture is in this study though...)

From what I understand the set studied was all White people.