There is at least ONE behaviorial marker that fits that bill. SDMB is what it rhymes with 
Actually, the data on this quesiton are already in. A massive study by Robert Plomin involving thousands of children taking regular intelligence tests and submitting to the best genetic screening available has been trying to match up genes with intelligence. The results are that they’ve not found a single genes that accounts for even one percent of the variation in intelligence. They’ve found six genes that may have some relationship to intelligence, but for all of them the correlation is so small that it may be statistical random noise.
The article does cite twin studies to back up the belief that genetics does play a role in determining intelligence. However, twin studies themselves are in doubt. The idea behind such studies is that if identical twins show more similarities than fraternal twins, the difference can only be explained by genetics. But there’s no sound reasoning behind this; there are any number of factors which could, potentially, drive the behavior of twins closer together. The above article concludes, “there is little reason to believe that twin
studies provide evidence in favor of genetic influences on psychiatric disorders and human behavioral differences.”
Personally, I would look at it this way. The twin studies do, generally, suggest a genetic link to intelligence and other products of the human mind. But the actual tests of the genome keep coming up blank, and that’s much stronger evidence against a genetic link, strong enough to overrule the twin studies. Bottom line: the 98% of us who aren’t twins should have some say in this matter too.
Genetics, culture, upbringing, luck, there are a lot of factors. I could have the genes to be the greatest tiddly winks player that ever was, but it means nothing if I never played it, or never even heard of it. A person could have the best brain in the world, but if he doesn’t use it, it’s worthless. What if your genes predispose you to be very very good at some thing that hasn’t been invented yet? Useless.
Genetics only gives a person the potential or talent for something. Nothing more. It is not the final decider of anything.
I’d be okay with my kids being gorgeous. That wouldn’t need any tweaking at all.
Maybe you missed your calling as a tiddly-winks player but I bet you could make a killing at quarters.
No, I just get drunk and fall asleep. Epic FAIL! 
*But the actual tests of the genome keep coming up blank, and that’s much stronger evidence against a genetic link, strong enough to overrule the twin studies. *
Have you seen this recent one by Thompson?
*The UCLA researchers took the study a step further by comparing the white matter architecture of identical twins, who share almost all their DNA, and fraternal twins, who share only half. Results showed that the quality of the white matter is highly genetically determined, although the influence of genetics varies by brain area. According to the findings, about 85 percent of the variation in white matter in the parietal lobe, which is involved in mathematics, logic, and visual-spatial skills, can be attributed to genetics. But only about 45 percent of the variation in the temporal lobe, which plays a central role in learning and memory, appears to be inherited.
Thompson and his collaborators also analyzed the twins’ DNA, and they are now looking for specific genetic variations that are linked to the quality of the brain’s white matter. The researchers have already found a candidate–the gene for a protein called BDNF, which promotes cell growth. “People with one variation have more intact fibers,” says Thompson.
Nothing new really. As ITR champion noted, it’s based on an the same old assumption that if identical twins show more similarities than fraternal twins, the difference can only be explained by genetics. But there’s no sound reasoning behind this.
It has the added problem that the article itself notes that this is a purely physical correlation, not a measure of intelligence at all.
And to compound it there is no still no genetic basis to the physical differences.
So basically we’ve got a measure of physical structure, that is unrelated to intelligence and unrelated to genetics that we can conclude may or may not have some underlying genetic cause based on a dubious assumption about twins.
Not what I would call compelling evidence of anything.
Were it not for the fact that a predominately genetic basis for intelligence carries with it social ramifications–especially if it is shown that the distribution of those genes varies among populations–there would be no controversy here at all. As it is, because it is a sensitive subject, all sorts of objections are raised when genes are advanced as the principle determinate for the maximum intelligence potential of an individual.
It’s easier to look at it the other way around, though, to approach the problem. This is a testable hypothesis. One can test the hypothesis that maximum intellectual potential is NOT primarily genetic by taking a given individual and exposing them to optimum nurturing influences. If they don’t turn out to be equal and, in fact, don’t turn out to be geniuses, then the delta is their genes, and the hypothesis that genes don’t control their intellect is disproved. Similarly, one can look at geniuses (any smart people, really) and determine whether or not their particular nurturing environment was optimal. If it wasn’t, then their intellect is innate.
You could, for example, expose this **Pedant **to optimal mathematical coaching (or, sadly, golf coaching). At the end of it all, I’d still just putter along. I was shorted when the genes governing that skillset were doled out to me.
We are our genes, mostly. Good nurturing can help us be better at something, but only to the limit of our genes, and those with better genes than I for mathematical ability need a lot less nurturing at math to be far superior to me.
As a medical educator, for example, I saw dozens of examples of bright kids with poor nurturing backgrounds catch up quickly as soon as they got into a good educational track. Others never caught up and just did not have the raw ability to master the material. There’s no question better nurturing and better education will improve on poor nurturing. But it won’t change your genes.
*Originally Posted by Blake
Nothing new really. As ITR champion noted, it’s based on an the same old assumption that if identical twins show more similarities than fraternal twins, the difference can only be explained by genetics. But there’s no sound reasoning behind this.*
Yes there is, identical twins share 100% of their genes, while fraternal twins share only 50%. If genes are important, identical twins should be more similar to each other than fraternal twins or ordinary siblings.
Thompson addresses some of the non-genetic factors and address possible biases in twin research on page 476 of this paper ’ Neurobiology of intelligence: Science and ethics. Jeremy R GRAY, Paul M THOMPSON Nature reviews. Neuroscience(Print) 5:66, 471-482.
http://www.loni.ucla.edu/~thompson/PDF/nrn0604-GrayThompson.pdf
It has the added problem that the article itself notes that this is a purely physical correlation, not a measure of intelligence at all.*
The speed of brain processes correlates with IQ, and brain speed is partially determined by the integrity of the myelin wrapping around nerve axons that make up the communication pathways (white matter) in the brain. The thicker the myelin, the faster the nerve impulses.
Also, see figure 3 ‘Linking genes, brain structure and intelligence.’ at top of page 475.
Gene effects on brain structure can be assessed by collecting MRI brain scans (left) from twins or extended families, and comparing volumes of grey matter (green), white matter (red) or cerebrospinal fluid (blue). Overall brain volume is 85% heritable and correlates with psychometric intelligence (0.33) (REF. 30). Genetic modelling has shown that g and grey matter volumes depend on the same set of genes (the genetic correlation is about 0.25). The volume of grey matter in each lobe is genetically influenced to different degrees (the volume of grey matter in the frontal lobe, shown at right in yellow and pink, is highly heritable). b | Genetic influences on brain structure can be assessed using statistical maps. In the classical twin design, a feature is heritable if within-pair correlations (typically called intraclass correlations) are higher for pairs of identical twins (who share all their genes, except for rare somatic mutations) and lower for same-sex fraternal twin pairs (who, on average, share half their genes).
…
c | Twice the difference between the MZ and DZ correlations (h2) is a simple estimator of the heritability of grey matter volumes at each location in the cortex. d | Statistical significance of the heritabilities. These can also be estimated from path analyses. Variations in grey matter volumes are strongly influenced by genetic factors, especially in frontal brain regions (for example, the dorsolateral prefrontal cortex). A subsequent study in a larger, independent sample found that variations in total grey matter volume were almost entirely attributable to genetic factors (but three-dimensional maps of these effects were not created). These genetically mediated differences in brain structure explain a proportion of the variation in general cognitive ability. This ability is also influenced by non-genetic factors such as education and nutrition, prenatal and family environments, training and environmental hazards such as lead poisoning.
`
There would be massive controversy. There would be far, far more. In fact orders of magnitude more, controversy than for the current issue. In fact it would be so controversial as to lead to a civil war between those who accepted the proposition and those who didn’t.
See, I can make baseless, totally unprovable assertions too. Doesn’t make for much of a debate though, does it?
1)How do you propose to take a given individual and exposing them to optimum nurturing influences? We know from studies conducted using half-siblings and surrogates that simply sharing the same womb accounts for between 40 and 60% of intelligence. Birth order within that womb accounts for another 15-20% and the sex of the previous occupant may determine a further 10%. And that’s before we start factoring in effects following birth such as the parent’s emotional state. So how do you propose to set up this experiment that exposes an individual to optimal conditions? You just said one can do this experiment, so please explain how?
2)How do you propose to determine optimal nurturing influences? It’s been well established that humans have different personalities and learn optimally in different was regardless of gross intelligence. So how do you propose to ensure that the conditions are optimal for any individual? You can’t test for it, since he act of testing in itself will produce sub-optimal results for many indivdiuals.
3)Since nobody is denying that there is, at a minimum, some gene X environment interaction that determines intelligence, how do you propose to eliminate that interaction? Because of course if you can’t eliminate that interaction with environment you certainly can’t claim that “ the delta is their genes:, can you? In case you don’t understand what a gene by environment interaction is I’ll give a hypothetical. Let’s imagine that a person has a particularly heat sensitive protein in their body. If the person is never allowed to overheat for prolonged periods no problem. But for every hour spent at air temperatures above 35oC their IQ drops by 1/1000th. Clearly this particular genotype will show much higher IQs in Alaska than they will in Honduras. How do you propose to account for this environmental interaction?
How can you do that? To give you an obvious example, we know that many teenagers only excelled once they were sent to prison. We know from their own testimony that the distractions in the wider world prevented them from focusing on learning. So do you conclude from this that being imprisoned is the optimal learning environment? Or do you reach a more rational conclusion that what is an optimal learning environment for one personality is at best mediocre for another? And if you do accept the latter conclusion then how do you you propose to “determine whether or not their particular nurturing environment was optimal”?
Were you? How do you know? How do you even know what optimal mathematical coaching is for you? Have you ever been to prison? If not then how do you know that you wouldn’t discover that you excel in prison, as many other prisoners have found? Have you ever been bedridden for years at a time? Descartes, was, and that was where he discovered that he excelled at mathematics. SO how do you know that isn’t also true of you?
This seems an absolutely ridiculous claim as stated. I can only you assume oyu mistyped it.
If it were true then the main reason why pre-Columbian Inuit never excelled at rocket science was mostly because they are genetically not adept at rocket science. The fact that they had never seen writing, much less a rocket, is secondary. It’s mostly genetic.
This is so obviously nonsense that the statement is refuted by that alone.
We are mostly our upbringing. If you raised a pre-Columbian Inuit in modern day New York she’d be a modern day New Yorker, regardless of her genes. And if I raised you infant in a pre-Columbian Inuit camp she would be a hunter gatherer with no ability to count or read… Your claim that people excel at hunting and gathering or rocket science mostly because of their genes is, well, it’s ludicrous.
Of course. But this says nothing at all about what those limits might be or how much they vary between groups.
No, they don’t.
Once again, I too can make baseless assertions.
As a medical educator can you explain how you determined “poor nurturing background” and “good educational track” without resorting to the obviously circular (and hence invalid) “one that allowed them to catch up quickly as soon as they moved to the other”?
Really your entire position seems to hinge on the assumption that there is a single, optimal learning environment for every single human being, and that there is absolutely no gene by environment interaction.
Because if we reject either of those two assumptions all those tests you say you can do, simply can’t be done.
“A implies B” does not allow you to conclude that “B implies A”.
When I hear thunder there is always a storm nearby. But when there is a storm nearby I do not always hear thunder.
If genes are important, identical twins should be more similar to each other than fraternal twins. But just because identical twins are more similar, that doesn’t allow you to conclude that genes are important.
To help you understand what I mean, imagine there was some intra-placental immune or hormonal interaction between fraternal twins that caused minor brain damage in one twin. If intelligence was 100% due to gestational conditions and 0% due to genetics, would you expect fraternal twins to have more or less mental discrepancy than fraternal twins/siblings?
Of course this is a hypothetical, but you can hopefully see why you can’t conclude that just because identical twins are more similar, that increased similarity must be due to the importance of genes. Identical twins share a lot more than just genes.
Do you wish to discuss these papers with reference to other poster’s positions and your own? Or are you just “reading them into the Hansard” as it were?
Correlation =/= causation. Chains of correlation from myelin density to neuronal speed to processing speed to intelligence are even less useful.
I repeat: the article itself notes that this is a purely physical correlation, not a measure of intelligence at all. When the author of the study says that it’s not a measure of intelligence, that’s probably the point where you should stop arguing that it is a measure of intelligence.
edit:
I say again: Do you wish to discuss these papers with reference to other poster’s positions and your own? Or are you just “reading them into the Hansard” as it were?
Of course this is a hypothetical, but you can hopefully see why you can’t conclude that just because identical twins are more similar, that increased similarity must be due to the importance of genes. Identical twins share a lot more than just genes.
Right, but how much variance do those other factors contribute? I understand prenatal factors have been narrowed down to about 20 percent of the overall variance from the various studies. In terms of shared environment Bouchard’s study of twins raised apart found they had very high correlations for various intelligence measures.
I repeat: the article itself notes that this is a purely physical correlation, not a measure of intelligence at all. When the author of the study says that it’s not a measure of intelligence, that’s probably the point where you should stop arguing that it is a measure of intelligence.
I’m not saying it is a measure of intelligence, simply that it is a physical correlate (like grey matter volume, cortical thickness etc). Although research seems to be increasingly identifying the physical basis for ‘g’ and scans may be used in future to supplement tests.
- We further validated this finding by generating a neurometric prediction model of intelligence quotient (IQ) that explained 50% of variance in IQ in an independent sample…
Our neurometric model of IQ contributes to a literature showing that brain images can be used to predict complex behaviors and traits (Haynes and Rees, 2006; Knutson et al., 2007). Although our model still does not approach the predictive power of psychometric tests, its high accuracy suggests that neurometric assessments of intelligence may soon become a useful complement to psychometric test. For example, brain images might be used to improve intelligence estimates for individuals whose psychometric scores systematically underestimate their IQ. We hope that future research will build on our neurometric model of intelligence, both refining it so that it generalizes to other populations and expanding it to enhance its accuracy.
That’s the whole debate in a nutshell. We don;t know and we have no way of knowing.
Nope, every study contradicts the last. Using embryo implant surrogates is arguably the best methodology, and it suggests that C40% can be explained just by sharing the same womb, but the data pool is small. Studies with half-siblings return results in the 40-60% range and are much more reliable. And that’s without invoking any other prenatal factors else at all. Once we add in things like nutrition, post-natal environment (which is effectively inseparable form prenatal) and so forth, we could potentially be looking at 80%. Or we could be looking at 20%, we just can’t know.
The highest reputable correlation I’ve ever seen based on twins studies is 70%. That might sound like a good correlation, but if we accept the low-end, 20%, figure for pre-natal influence then identical twins have only a 50% genetic correlation for intelligence, despite a >99% correlation for genetics. That is in keeping with the bulk of the other evidence, which suggests that intelligence is at best 50% heritable.
What that means is that if you try to use genetics to predict which if two people is more intelligent you will do no better than you would by tossing a coin.
Right, it’s a correlate. And one that doesn’t work nearly as well as other correlates such as parental income or education. Which is rather the point.
I’ve seen no evidence that would lead me to such optimistic conclusions. We still can’t even define what this nebulous “g” is, so I have a hard time believing we are able to identify a physical basis for it.
I ask for the third time: Do you wish to discuss these papers with reference to other poster’s positions and your own? Or are you just “reading them into the Hansard” as it were?
What do you think occurs? You must *some *idea at least as a hypothesis to ground the views you’ve expressed on this topic before. Do you think that Gene X, Y, Z is required for intelligence but differentially active among ethnic groups? Is it just one gene you think governs potential? two? three? five? I want to understand your calculus.
- Honesty
This was a fascinating read. I’m going to bring this to my statistics professor who claimed two lectures ago that an e2 value can never be negative (yet the aforementioned paper gives an r2 of -3.3) and beg for extra credit.
*That is in keeping with the bulk of the other evidence, which suggests that intelligence is at best 50% heritable.
What that means is that if you try to use genetics to predict which if two people is more intelligent you will do no better than you would by tossing a coin.*
Remember that the term “genetic” is very broad, while the term “heritable” is very specific. Heritability is the proportion of trait variance within the population explainable by variance of genes. To say that a trait is .5heritable does not mean that it is caused 50% by genes, . Rather, it is to say that 50% of the variance within the population can be accounted for by the variance of genes within the population.
Right, but how much variance do those other factors contribute?
That’s the whole debate in a nutshell. We don;t know and we have no way of knowing.
For papers on how you can figure this out I’d recommend Heritability and Causality, Philosophy of Science 60 (1993), pp.396-418 by Neven Sesardic.
http://www.ln.edu.hk/philoso/staff/sesardic/publications.html
In terms of ‘g’ there was a good discussion recently on Steve Hsu’s site here.
Chen019,
-
Don’t try to teach your grandmother to suck eggs.
-
I ask for the fourth time: Do you wish to discuss these papers with reference to other poster’s positions and your own? Or are you just “reading them into the Hansard” as it were?
Having a discussion with someone whose sole contribution is to post links is dull and I’m disinclined to continue if that is all you intend to do.
I don’t know which, or how many, genes govern intelligence. It is my personal WAG that it will be simple enough to reasonably unravel, and that the gene set governing g, for instance, will be closer to a handful than a hundred.
I note differences in measured intelligences across various populations.
I note differences in success rates for pursuits requiring a specific skillset across various populations, even when the confounding effect of nurturing is reasonably accounted for.
I note that some individuals, when exposed to better nurturing, achieve more than the next individual exposed to the same nurturing–picture me and Kobe Bryant, for example, both being exposed to the same basketball nurturing. We would not come out the same, and the difference is genes.
As to genes coding for intellect and their distribution among ethnic groups…well that’s the premise of the OP, isn’t it? When the putative genes are identified, we’ll be able to quantify their distribution among various groups. And then we won’t need to speculate.
I’m OK with waiting. I am confident of being correct that there will be significant distribution differences for all sorts of genes among various groups (there already are) but I will certainly change my position if I am proved wrong. I encourage those who argue that genes must be sort of evenly distributed among all “ethnic groups” to be careful about staking too much with that position, since the elaboration of the genome and the lowered cost of broad-scale testing are likely to settle the argument in a concrete way–the point of the OP, I think.