Reaction Times and IQ Tests

The following is a guest post by Stephanie Zvan. In this post, Zvan addresses a recent study of "reaction times" and IQ measurements in two study groups distinguished by race. I'll let the post speak for itself, but it is worth nothing that in the ongoing discussion of race and intelligence, the complaint is commonly made that critiques of mainstream psychometrics do not pay much attention to the recent literature. This would be a case of that not happening.

Reaction Times and IQ Tests

Stephanie Zvan

In the ongoing discussion about disparities between racial classifications on IQ tests, Dr. Bryan Pesta requested that we consider his paper, "Black-White differences on IQ and grades: The mediating role of elementary cognitive tasks." Because as he rightly points out, not everyone will have the background to evaluate the paper, I thought it would be helpful to discuss the paper in the context of the cognitive science literature.

The Study

There were three tests given to the participants (139 white and 40 black students who received course credit for participation). The first was a very short IQ test, clocking in at 12 minutes. However, its creators do say (it's a proprietary test) that it has a high g factor loading. This means that it correlates strongly with other IQ tests despite its brevity. For a good discussion of the history of g and what this correlation means on its own without further study, I highly recommend this post by Three-Toed Sloth. The study currently under discussion was an attempt to show what g is in more concrete terms.

The other two tests were computer-based reaction-time tests. Test one was an inspection time test, in which participants were shown a pair of lines for a set, very brief time and asked to indicate which was shorter. Series of correct answers resulted in the time being shortened. Any incorrect answer would result in the the time being lengthened. Test two was a reaction time test, in which participants were asked to indicate the position of the stimulus (a letter A in this case) as quickly as they could.

There were significant differences between race groups on all measures, with blacks scoring worse than whites on average, and the authors found that the variability in a factor derived from the timing test scores accounted for the variability in IQ test results.

The Context

Reaction time experiments have a long history in cognitive psychology. If you want to know more about it in detail, Dr. Andries F. Sanders literally wrote the book on the subject, Elements of Human Performance: Reaction Processes and Attention in Human Skill. If you're interested in a somewhat lighter overview than nearly 600 pages, Dr. Robert J. Kosinski maintains a good bibliography and overview.

What is important to take away from either the short version or the long? Two things. The first is that reaction time is largely a function of attention (thus the title of Dr. Sanders' book). This means that reaction time is strongly influenced by factors such as fatigue, stress and distraction. This study makes no effort to control for these factors despite the existence of an extensive literature on this subject, and despite their being racial differences in hours worked by college students (although what the exact direction of the difference would be in this case is unclear). They do control for age and sex, which are also known to affect reaction time.

The second is that, with practice, reaction time tasks show a decrease in errors, reaction time, and variability in reaction time. Because of this effect, Sanders stresses the importance of adequate practice times. Pesta's study included three practice trials for the first timed test and six for the second, which may not be enough if one group of students has significantly more practice in reaction time tasks, like high-twitch sports or video games, as reaction time tests do show some transfer of practice effects between related tasks. Although the authors do not discuss it, the case for more pre-data-collection practice is also supported by the fact that the group with the longer reaction times showed a higher variability in times.

The Claims

There is an additional context to be considered with regard to this study, which is the difference between the claims made in a modest, undercontrolled study like this one and the claims made by the scientists outside the journals in which these studies are published. In building the case that racial-grouping IQ test differences are immutable or genetic in origin, qualifiers get left out and connections are made that aren't supported by the literature.

What does Pesta have to say in the Discussion section of his paper?

The variation in both ECT performance and IQ scores seems largely driven by individual and group differences in the general factor. On the other hand, more than g contributes to a person's GPA, including variables like motivation, conscientiousness, family environment, work status, etc. (though recent research also points to a genetic cause for within-group differences in academic achievement, see, e.g., Luo, Thompson, & Detterman, 2003; Wainwright, Wright, Geffen, Luciano, & Martin, 2005; Wainwright et al., 2006). Considering just the present data set, however, basic measures of information processing do little to explain the Black-White difference on GPA.

Although consistent with Spearman's hypothesis, our data offer no insights as to possible causes for race differences on the ECTs. Whether these differences might arise from differences in environment, nutritional levels, genes or some other factor is an issue in need of further study. Further limits to the present study include: (1) a relatively small sample size for Black students, though statistical power did not seem to be an issue given the pattern of consistent, significant results was found. (2) A restricted range of participants, as we ran only college students. (3) Use of WPT scores as a proxy for g (i.e., we did not derive g factorially). Future studies with multiple measures of g might show an even clearer picture of the mediation effects reported here. (4) For unknown reasons, both age and gender differed by race. Although we included each as control variables in the mediated regressions, a more random sampling of race in a future study would offer stronger evidence that neither played a role in the data patterns reported here.

What does he have to say when he discusses the study elsewhere?

Easy to explain (though the explanation may not be correct) if you believe that IQ is some basic index of how people differ in how fast and capable their brains process info.

I really think my one study in the area cannot speak to the cause of the difference. It was never intended to do that. It shows that paper and pencil differences are explained by information processing ability, but not why.

No single study is obligated to answer all questions that might arise, especially those it was never designed to address.

So, I really don't know why races differ on average in cognitive speed. I suspect it could be nutrition, prenatal development or something else-- possibly genetics, but I don't know.

I take how fast a neuron fires to be fairly biological, but not necc. genetic.

You can trace the raw paper and pencil IQ difference back to race differences in performance on tasks requiring nothing but mental speed. Even the speed with which one neuron in the brain fires correlates with IQ.

My measures are cognitive (reaction time) and not biological (some type of blood test or whatever) but I think the inference that choice reaction time reliably and validly measures brain speed is reasonable.

So now we've moved from a measure of attentiveness to a measure of information processing ability, specifically the speed at which neurons fire. Where is the evidence to support this? Um, evidence? You know that it's awfully invasive to measure the speed of individual neurons, right?

There is a recent technique that can measure the myelination (insulation by fat that causes impulses to be conducted more quickly in nerve cells) of various parts of the brain, however, and a study has found increased myelination in the brains of people who perform better on reaction time tests. On the other hand, given that the conduction boost was found in the areas of the brain related to vision, it would be premature to take these results as a confirmation of g as a measure of intelligence. And given the plasticity of the developing brain, it certainly has nothing to say on whether there is a genetic link to performance on these tests.

PESTA, B., & POZNANSKI, P. (2008). Black-White differences on IQ and grades: The mediating role of elementary cognitive tasks Intelligence, 36 (4), 323-329 DOI: 10.1016/j.intell.2007.07.004

Planty, M., Hussar, W., Snyder, T., Kena, G., KewalRamani, A., Kemp, J., Bianco, K., Dinkes, R. (2009). The Condition of Education 2009 (NCES 2009-081). National Center for Education Statistics, Institute of Education Sciences, U.S. Department of Education. Washington, DC.

Sanders, A. F. 1998. Elements of Human Performance: Reaction Processes and Attention in Human Skill. Lawrence Erlbaum Associates, Publishers, Mahwah, New Jersey.

Tuch, D. (2005). Choice reaction time performance correlates with diffusion anisotropy in white matter pathways supporting visuospatial attention Proceedings of the National Academy of Sciences, 102 (34), 12212-12217 DOI: 10.1073/pnas.0407259102

More like this

Is it just me, or don't the proponents of bigotry ever have anything substantial to trot out when they make claims of racial differences in intelligence? "Oh, we did an IQ test - de niggas, dey dumb!" Yet out in the real world I see no obvious differences; the biggest differences I see are between people who have had a good education and a good environment to study in and people who don't have much of a chance to learn because they're starving or their parents are fighting all the time, and so on - and that has nothing to do with skin color - merely correlation at times, but no evidence for causation.

By MadScientist (not verified) on 27 Dec 2009 #permalink

This is interesting, but not surprising. These two articles address some of the effects of what they call âstereotype threatâ, which does lead nicely into the article Stephanie cited from PNAS on MRI diffusion results.

The mechanism for the observed anisotropy in water diffusion observed in MRI is not understood. My hypothesis is that it is not âdiffusionâ of water per se, but rather transport of water via active mechanisms. My hypothesis is that it is primarily changes in those active transport mechanisms that produce the characteristic water diffusion anisotropy and also the white matter hyperintensities which are characteristic of reduced energy status in the brain. The white matter is mostly axons. Axons are extensions of cytoplasm elongated for long distances, inches or even longer. These extensions extend from the cell body to other brain regions and make connections at the tippy end. It is down these axons that signals propagate via the action potential.

Because the cell body of the neuron contains the nucleus and all the protein synthesis machinery, that is where the neuron makes all of the stuff it needs to for survival and proper function. Once stuff is made, it is carried out the axons to the tippy end via ATP-powered motors. There are suggestions that half the brain ATP production goes into powering these motors.

My hypothesis is that under conditions of insufficient ATP, turning off/down the ATP powered motors that transport stuff in axons is one of the first things to the cell does. During an ATP crisis, anything that takes longer than the crisis can be shut off to conserve ATP. A âfight or flightâ state is a state of reduced ATP, the ATP level is reduced to allow diversion of ATP resources to more immediate needs, the apocryphal ârunning from a bearâ example that I like to use. Of course there are all sorts of degrees of this, and individual regions of the brain are controlled locally because overall the whole brain cannot be allowed to fail. Better to restrict activity in non-essential areas and accept degraded performance so as to survive what ever threat is being dealt with.

Reduced transport of stuff by ATP powered motors in axons results in reduced entrained cytoplasm which results in reduced anisotropic movement of water, which shows up as white matter hyperintensities and which is interpreted as reduced water diffusion.

So, the âstereotype threatâ which causes reduced performance on a variety of cognitive tests is consistent with an acute stress response. The âstereotype threatâ could easily have been invoked in this study in the informed consent documents simply by stating the purpose of the study is to investigate any correlation between IQ, reaction time and race.

What is especially interesting (and not mentioned in the discussion) is that the GPAs were significantly different by race, and did not match the IQ differences by race. In other words, race exerted an effect on GPA but not via IQ. This would be consistent with black GPA being reduced by bigotry or by âstereotype threatâ. It is not consistent with a reduction in black GPA by IQ because IQ was corrected for. It is interesting that the finding that IQ was not related to GPA was not considered important.

That the standard deviations in the data from black students was higher, indicates (to me) less homogeneity in the black group than in the white group perhaps indicating greater confounding differences in training as Stephanie mentions.

Is giving course credit for participation as an experimental subject appropriate?

A colleague of mine (i work in the general arena of individual differences and developmental psychology) recently presented some data on a large sample of reservation-dwelling native american children showing rather large disconnections between standard IQ-test performance across age (which looked worse and worse), but typical developmental increases in measures of executive function that would also tap attention. Note that these aren't my data and they are currently under review at a top-tier developmental psych journal. However, that kind of finding suggests a 'wasting' of basic cognitive resources among disadvantaged groups. It would be interesting to see similar developmental studies as they are somewhat more informative, to me, than are the single-shot cross-sectional comparisons of college student samples.

By Monisha Pasupathi (not verified) on 27 Dec 2009 #permalink

Once again, Stephanie... Thanks for taking this on. Shame that it is necessary.

When my older son took the entry exam for an elite private HS the interviewer noted that he did not finish the test, but nearly all of the items completed were correct. When asked why he did not complete the test, he stated that he wanted to 'get the answers right'. He was admitted to the school, where he did very well academically. My African American son with an IQ of 130 now has an MBA and when confronted with a problem, takes the time to analyze the problem, he may not be the first finished, but I would trust him to be able to see all of the angles and come up with the best answer. I am not impressed with the 'speed' test to prove anything other than levels of stress and problem solving styles.

gwen, I am sure you are proud of the "130" on his IQ, but I think I would rather place an emphasis on the MBA. I am not, as a layperson who has learned a great deal from Greg and Stephanie in the recent discussions on IQ here and at Quiche Moraine, impressed with the speed factor of IQ tests.

Nor the GRE, the LSAT, the Iowa Basics, PSAT, ACT, etc etc etc.

Trying to figure out what "intelligence" itself means is a matter of both semantics and definition. Measuring it, well, that's a process that has been misused and abused to the point where it is necessary to mention your son's race and IQ in the same sentence just to defend the idea that race-based intelligence tests are spurious.

The Wonderlic test is a speeded IQ test, as are any of the brief tests (Raven's Advanced Progressive Matrices being another, more widely accepted example). The standard Wonderlic involves answering 50 questions with a 12 minute time limit. So, naturally, there will be a relationship between speed factors and these scores, but this relationship is neither compelling (to me), nor overwhelming (to statistical or practical outcomes).

So if the speed factor mediates the relationship between race and IQ, isn't the natural conclusion that the relationship between race and IQ is neither compelling nor overwhelming?

Sounds like there's a bunch of data showing that certain *tests* have differences, but obviously there's a ton of qualifying conditions that can always be brought up (upbringing, different stress levels amongst subjects, biased tests).

I agree with many of the caveats with this study, and the narrower interpretation of the results. However, most of what I've read is just this, dissections of how the research on this subject is flawed. And while that's important to recognize, I'm curious what you guys think the research *actually* suggests? I.e., what's the evidence (overall) for whether genetics has any significant role in brain functionality (between races to keep it simple)?

I love to see such careful, conservative science that refrains from overreaching (woohoo!!). But still, I'm curious to see what people like Stephanie and Greg actually think is happening here. I get the impression from Greg that he thinks it's pure environment, that genetics plays no role in IQ - am I correct?

I'm an admitted outsider who can buy into the flaws with much of the research that's been posted - but don't leave me hanging! Forgive me if there's already been posts about this, just point me in the right direction...

Elfie, I expect I'll be blogging on this topic off and on for a while, but I don't know that any posts I'm thinking of would answer your question about what I think. Frankly, I don't know whether there is any there's any genetic causality in intelligence aside from the cases Greg has mentioned elsewhere in which basic requirements for the continued healthy operation of the brain aren't met.

That being said, I am fairly confident that genetic differences between races that lead to differences in intelligence should not be the null hypothesis. It contains too many separate claims that haven't been well-studied for political reasons. Race has been a fluid concept over time, varying by social norms that have no plausible connection to genetics. Genetic testing that claims to show the existence of distinct races uses sampling techniques that don't correspond to the current and historical isolation of its subjects and often samples so many sites on the genome that one would expect some "significant" differences by chance alone. The genes identified in these tests have not been identified by function, if any. No genes have been identified as accounting for variability in normal brain function. Brains can vary wildly in structure without outwardly noticeable changes (Google "brain plasticity" and hydrocephaly). The work hasn't been done to validate differences in intelligence as a product of the structure of the brain. Intelligence doesn't even have a consistent definition that is based on the activity of the brain.

I've probably skipped a couple of steps, but all of those are necessary to tie racial genetic differences to differences in intelligence. Until that happens, I'm sticking with the null hypothesis, which is something that we as a society haven't done well. What has been shown to cause differences in IQ tests across racial groupings? That I'll almost certainly blog about because it isn't any one thing.

As a test of intelligence, I suggest we take a group of whiteys and give them an IQ test. We also give an IQ test to people from a community in the African jungles - or deserts - it doesn't matter. Then we take these two groups and leave them on their own to survive in that environment; the ones left alive after a month win the intelligence test. If that sounds stupid (and it should), it's far more sensible than a lot of stuff people put out there.

Rather than claiming to "test intelligence" I would say people need to be more specific and state what particular skills they are testing - for example in the cited study it is reflexes to a visual stimulus. Big whoop. Personally I wouldn't pit my visual reflexes against any pro baseball player regardless of skin color - they'd all twitch far quicker than me. In fact I'd say that reflexes is a pretty bizarre substitute for a measure of intelligence. When it comes to other skills such as working with abstractions, I know from frustrating experience that there are some artisans out there who are among the best in their craft and yet are utterly incapable of dealing with basic abstractions. As the saying goes "there are more obvious differences within a group than between groups".

By MadScientist (not verified) on 27 Dec 2009 #permalink

Speaking of baseball, if you're born in the US, you have a much better chance of making the major leagues if you're born in August, and a much worse chance if you're born in July. Is it a logical leap to make that Julians are genetically inferior athletes to Augustians?

As far as I can see, nobody has mentioned the fact that "races" (i.e. subspecies) are not valid natural categories, and therefore any attempt to correlate them with "intelligence," which itself is a folk category, is doomed. What these attempts to demonstrate, I think, is our culturally based fascination with ranking people.

I threw this one out there on a previous thread and Laden blew it off; maybe his guest co-blogger/bff would have a look?
[Note that contrary to Laden's condescending assumptions, I have no interest in demonstrating intelligence differences among any groups; I merely find the claim that there can be no genetically based variation in "intelligence" among individuals to be silly.]

By Sven DiMilo (not verified) on 28 Dec 2009 #permalink


There is far more evidence for non-genetic effects affecting intelligence than for genetic effects. Nonetheless there certainly can be genetic effects other than those associated with pathology (for the most part pathology is irrelevant to this discussion). The only time evidence seems to emerge that links the genetic effect to race is when the test categories are racial, and the effects tend to be small.

Intetroup differences in IQ that are seen in US society, for instance, are too large to be explained by the sort of effect shown in the paper you cited.

Sorry if you thought I blew it off. I don't have the time to respond to every single comment, as much as I'd like to.

Ron, regarding race categories, I certainly have mentioned that (though not in this thread) but thanks for pointing it out.

Sven, that study means that the possibility isn't ruled out. Twin studies are very good for ruling out genetic causes, but for reasons discussed in the previous thread (i.e., degree of shared prenatal environment, action of traits known to be genetic on the environment), they are insufficient to prove a genetic link. From what I can see of this paper, since I don't have access to the whole thing, it doesn't go beyond that. As the authors themselves note in the abstract, they've identified a possible genetic link to look for.

One note about the kind of imaging done for that study. It's the same type used by Tuch, showing structural differences in the brain that correlate with performance on reaction time tests. These are the tests that show a very strong effect for sex: women tend to be much slower at the task than men. That makes it very tempting to attribute these differences in brain structure to the effects of sex hormones, at least partially.

However, having repeated this kind of testing over the last several decades, we can now observe that the performance gap between men and women has been shrinking as women have become more involved in sports. That doesn't mean we can now say there is no effect of sex hormones, but we do know we need to be very careful in our assumptions that we've appropriately screened for environmental differences before we go looking in our genes. It's really, really hard to overstate the inherent plasticity (and reactive plasticity) of the brain.

I agree with Frank, I am not impressed with the speed factor in test taking either. It is extremely rare that time is a limiting factor in making intelligent decisions. What is important that one figure out how much time one needs to make an intelligent decision.

In thinking about it, the idea that this paper shows a difference in neuronal firing time or velocity of nerve propagation is not correct.

Nerve conduction evolved in deep evolutionary time. There are enormous pressures for nerve conduction to be as fast as possible consistent with proper function. If there were even a small difference between blacks and whites, that would show up in activities where there is the greatest need for rapid nerve conduction and processing, and where nerve conduction pathways are long, for example in professional sports that require tremendous eye-hand coordination, for example tennis. Are there any sports with a high eye-hand coordination component that are dominated by one race or another? I donât think so. There are black and white tennis players, black and white baseball players, black and white basketball players.

What all of those sports require is training. The mechanism by which training reduces reaction times is not by increasing the conduction velocity of nerves (mostly), or shortening the response time of synapses. Training reduces reaction times by shortening the neural pathway by neuronal remodeling and by reducing the number of synapses the signals must go through by neuronal remodeling.

I find it very doubtful that there is significant dispersion in nerve conduction times or in synapse reaction time due to genetic variations in the human population. Those factors are too important to be regulated by open-loop control via direct gene action. There must be feedback control mechanisms that regulate the nerve conduction velocity in specific tissue compartments. There are mechanisms that adjust nerve conduction velocity, for example myelin thickness. Nerve conduction velocity has to be regulated. The nerves that fire muscle cells have to trigger them all in sync. In motor neurons, the cell body is in the spine and it is the axon that reaches all the way out to the muscle. The time delay is all in the conduction velocity of that motor neuron axon.

If there were significant polymorphisms in genes that regulated nerve conduction velocity, then âhybridsâ would have reduced fidelity of control because nerve conduction velocity is too complex to be regulated by a single gene. Numerous genes must work in concert; they must have co-evolved to work in concert to produce the âoptimumâ trade-off of speed and reliability. The hypothesis that there are significant black-white differences in nerve conduction velocity implies that blacks and whites have different constellations of genes that have co-evolved separately. If so, then âhybridsâ should have reduced nerve function because genes transferred from one constellation to the other will not work âin syncâ as well. It is not observed that âhybridsâ have degraded nerve function over âpurebredâ blacks or whites.

I think the hypothesis that there are significant nerve conduction velocity or synapse reaction time differences between blacks and whites is highly implausible.

How is race defined, exactly?
Shouldn't the researchers have had an exact definition before they started?

I read Dr Pesta's paper, and he does not seem to define what he means by "race" but it is unlikely that his results could map in any realistic way to real genetically distinct populations. His methods section says that

"Race was self-reported from among the following categories: White, Black, Hispanic, Asian, Indian, and Other"

. These students have been asked nothing about their genetic inheritance, and there is no indication that their genetic makeup has been sampled or tested in anyway. They have simply been asked to assign themselves a cultural "label" - and define which cultural grouping they feel most integrated with.

How would Obama, just to name a well-known example, answer this? He could self-define as either "Black" or "White", with equal genetic "truth". But, in the US, "Black" is a broader, more inclusive cultural category, and easy to get into - only one African parent or grandparent is required. On the other hand, "White" is a much more tightly controlled, exclusionist cultural category - a single African parent or grandparent would exclude you from it. This would appear to be the reason that most Americans regard themselves as having elected a "Black" President, his "White" mother notwithstanding.

The fact is that these cultural labels of "Black" and "White" continue to have cultural meaning and consequences within the US, and that the apparatus for maintaining a preferential access to educational and material success for the more exclusive cultural grouping of "Whites" has not yet been dismantled, means that any correlation between higher IQ, educational success, material success and "Whiteness" is self-confirming.

Dr Pesta appears to have adequately shown that self-defined "Whites" are somewhat better at being "White" (with all the cultural baggage that that entails) than self-defined "Blacks." A not particularly surprising finding, given that the latter self-definition must arise more from a sense of being excluded from the first category, than from any facts about an actual genetic inheritance.

Elfie, the problem isnât with what people think, but with what people do. Race based maltreatment has always existed and still does. We know that virtually all of the justifications for that maltreatment in the past were completely bogus. It is not at all clear that current justifications for maltreatment are not also completely bogus. Certainly many of them are. I think that a great deal of skepticism is justified in evaluating claims for racial or genetic differences that are used to justify differential treatment.

The notion that âintelligenceâ can be reduced to a single factor g, and that g can be measured in tests has not been demonstrated. âSomethingâ can be measured in tests, and that âsomethingâ has certain properties, but the case for that âsomethingâ being an actual measure of the concept thought of as intelligence has not been successfully made. Spearmanâs hypothesis was refuted by EB Wilson in 1928. That refutation has never been addressed. The link that Stephanie gave shows quite well that g is a statistical myth. It is an artifact of how g is calculated. Unless the proponents of the use of g can address those issues, it is correct to reject using g for anything important.

I think that most scientists would agree that myths should not be used to influence public policy. Not the various creation myths, not the various doomsday myths, not myths about demons causing disease, not the myths that imbalance in the four humors causes disease, not the myth that there is a âgâ factor that measures intelligence.

IQ tests are always given in a social context, and social context has been shown to measurably influence the results both up and down. When people are given reasons to not do well, even when the reasons are known to be bogus, they do not do well. This has been well demonstrated in the effects on the mathematical ability of women, where hearing the suggestion that women are not good at math does reduce the math test scores of women.

We know that âintelligenceâ is the property of a phenotype. Lowering intelligence is easy to do; any number of toxins will do it, nutritional deprivation, abuse, isolation, maltreatment, brain injury, and in the data on mathematical ability in women, simply being told that one is a member of a group that isnât good at what is being tested.

Greg had a good question on the other thread. âWhy?â…

If high âintelligenceâ is a good thing, or in fitting with the theme here, doubleplusgood then shouldnât we be trying to increase it every way that we can? To me, that means trying to maximize all of the things that we know have an effect, some of those effects are quite large, prenatal nutrition, reductions in abuse and maltreatment, better education, and so on. There is no controversy that better prenatal nutrition increases adult intelligence. Why is instituting programs for improving prenatal nutrition so difficult? Why is improved daycare so difficult? I suggest, largely because of the myth of g gives a pseudoscientific rationale and cover for xenophobia.

I think the proponents of the concept of a âgâ that is genetically determined and which is a measure of intelligence need to explain to the rest of us why. I understand why the YECs promote the myth of ID and want it taught in the schools. Why is the myth of g being promoted?

I understand that Bryan prefers not to answer on Gregâs blog. I cannot access Stephanieâs blog while at work, so can only read posts there in the evening. I look forward to hearing the answer to the question why.

I apologize for the gratuitous snark in my previous comment.
The only reason I said you "blew it off" was that after I posted this seemingly relevant quote:

In a cross-trait mapping approach, common genetic factors mediated the correlation between IQ and white matter integrity, suggesting a common physiological mechanism for both, and common genetic determination.

you said this:

I'm still waiting for evidence of genetics connected to intelligence.

I am operating on the very edge of me knowing what I'm talking about here, so I'll comment once more and then shut up.

There is far more evidence for non-genetic effects affecting intelligence than for genetic effects. Nonetheless there certainly can be genetic effects other than those associated with pathology

Fair enough. I can agree with all of that.

Twin studies are ... insufficient to prove a genetic link.

*shrug* You set a high bar then. That's cool.
Just curious: can you identify hypothetical criteria that you would accept as "proving" such a link?

One note about the kind of imaging done for that study....

What follows is a red herring (in terms of my point). The study had nothing to do with reaction times.

It's really, really hard to overstate the inherent plasticity (and reactive plasticity) of the brain.

Of course, that's true.
It's also the secret-escape-trap-door I mentioned earlier. People with an ideological opposition to the concept of genetically based variation in intelligence can always use plasticity as a last-ditch argument when empirical variation in brain structure and function is reported.

I find it very doubtful that there is significant dispersion in nerve conduction times or in synapse reaction time due to genetic variations in the human population.

*shrug* Argument from personal incredulity fail.
Motor neurons are a total red herring (Schwann cells vs. oligodendrocytes for one reason).

By Sven DiMilo (not verified) on 28 Dec 2009 #permalink

These are all good questions, and I don't have time to address this issue now in a comment. (Suddenly I'm inundated with numerous things demanding my attention).

So for now, consider this: Is height genetic? I.e. will parents resemble their offspring in this regard because of genes being passed on? Any basic college textbook on a related topic will say it is and show a graph or two indicating that it is.

Variation in stature in humans found in one generation is closely correlated to that variation seen in the parents, with that variation being measured in a few inches at most.

However, in the US, we have this pattern of immigrants getting taller over time. Italian immigrants in 1880 average a height several inches less than their great grand offspring following this change in height. The difference between the immigrant generation and the post-immigrant generation (say three or four generations later) is closer to a foot than to an inch. The variation we can explain linking parents and offspring is closer to an inch than to a foot.


Don't forget to name the genes involved, and describe the developmental processes involved.

Hint: I kno of only one gene that is linked diretly to stature in any way other than pathology. There may be others that have been discovered since last time I looked a few years ago. But the textbooks I mention above that plainly and confidently tie genes to stature in a very simplistic way would predate the discovery.

Explain, adequately and with no arm waving or mad up shit, the relationship between stature and genetic in humans. Then we can move on to IQ.

Sven, I want to see active proteins differentially encoded for in genes. You know, evidence of genetic differences.

Yes, that's a high bar. It is a high bar for a reason. Well, two reasons, the most important and fundamental being that the attribution of differences to genetics has real-world consequences, meaning that we want to be very sure of that. The second reason, which is actually the one I originally meant, is that I'm applying some strong skepticism to balance a whole stack of attributional biases. We "want" to underestimate the role that environmental factors have on others, which means that if we want to maintain rationality, we need to work hard at understanding and accepting them instead of just saying, "Oh, that makes sense to me."

My "red herring" was an example of us not working against those biases.

Sven, the hypothesis that: nerve conduction speed is under direct genetic control and that there are significant differences in nerve conduction speeds between blacks and whites and that the black/white significant difference in nerve conduction speed is due to different genetics makes certain predictions.

The absence of any data that there are nerve conduction speed differences between blacks and whites, the absence of any well documented genetic differences between blacks and whites related to nerve conduction, and the absence of any data on how nerve conduction speed is regulated by genetics makes the hypothesis doubtful.

In addition to the lack of data supporting the hypothesis, when predictions made by the hypothesis are not observed it is not personal incredulity that makes the hypothesis highly doubtful, it is a lack of evidence and evidence to the contrary.

If you can cite some links where there is data on nerve conduction speed, on genetics of nerve conduction and on black-white genetic differences, we can evaluate the hypothesis in light of that data. In the absence of data, evaluating the hypothesis in terms of personal credulity is a fail also.


"I suggest we take a group of whiteys and give them an IQ test. We also give an IQ test to people from a community in the African jungle"

you mean some blackies?

It sounds a tad unfair to give the blackies the home team advantage. That is not a fair test.

(interesting - my spell checker won't accept blackie but is okay with whitey)

On a serious note, the whole IQ test comparison test thing is crap because the tests can only be compared if the people taking them are from similar backgrounds, places etc and took the test at the same moment in time. They are not designed for cross cultural comparison.

I wonder if the speed element being discussed in the current thread could be related to confidence and experience with tests? Many immigrant groups experience dramatic improvements in IQ along with increased height in a few generations.

My own white ethnic group was accused of bringing down the IQ scores of several states at one time. My working class parents managed to get us into decent public schools and to emphasize education, and the average IQ of my siblings at least is way above average. This happens all the time.

IQ tests can be useful for comparisons within a homogeneous group but that's it.

What everyone here is dancing around is that when you take a population group with variation, separate and relocate portions of that population group in different ecological environments and subject them to divergent selective pressures you're going to get divergence of mean traits. And what's with the misuse of really simple terms? It is not bigoted to claim that there are niche/average differences between brain functioning of different population groups. Now, if you attempt to project some notion of worthlessness onto a group due to their niche/average, then, sure, that'd be bigotry. And what's all this about the Mismeasure of Man? It's a decades-old book that IIRC targets 40(?) percent of its criticisms at stuff written in freakin' 19th Century!! Why do you think Gould found it necessary to talk about guys writing well over 100 years ago? Understanding in many fields is advancing at amazing paces, and you're diddling yourselves over relatively ancient stuff.

Geez, what an anti-knowledge blog you got going here. Hey, major props for giving the Young Earth Creationist types a run for the money on abject stupidity.

Ecological divergence ==> Genotype divergenece ==> Phenotype divergence

Asher, your understanding of evolution, genetic variation, development, and neurobiology is roughly 11th grade level.

Although I have yet to have made a comment regarding Gould's book (on this blog, ever) I'll make a quick one here: The value in Mismeasure of Man (which is indeed a mediocre book, as are all of Gould's, from a scientific point of view, but good reading if you like his style) is in exploring the history of this concept ... of racial differences with Euro-Westerno-Whito-Normative supremacy. It still has value in that area. The truth is that white supremacists (which is what we call them now) have been playing the samme tricks all along, including crying "that's not really szienzeee!!! aIEEEEE!!! whenever they are faced with some real science, and including falsifying te nature of pre-existing writing to suit their own ends, and including ... measuring things wrong.

I submitted an article for publication awhile back, and to be balanced, figured I'd cite Gould in my intro.

From an Anonymous reviewer:

Why Cite Gould? The man is an idiot. He's an advocate not a scientist. Would the authors cite a young earth paper in a manuscript on geography?

I took the Gould cite out.

But surely this is the single most bad ass comment I've ever come across from peer-review.

I meet Asher before. Let's understand who this person thinks:

âNope, Iâm an atheist, whose taxes pay for a societyâs infrastructure that carries and supports millions and millions of individuals who contribute nothing. They vote with their open maws, their âsocial justiceâ is shoved down my throat. If I were a 17 year-old rutting sow, spreading my ample thighs for any gold-chained thug with a swagger, and having three children by three different ex-cons, Iâd be everyoneâs darling. The so-called conservatives would be begging me to just have the baby and the so-called liberals would be throwing as much money at me as they could possibly wring from the productive class.

I just want life-types, such as myself, to band together and turn the tables.

Once limited, constitutional government ends, in the US circa the New Deal, justice is nothing more than who is fucking whom. Itâs better to be the fucker than the fuckee. My goal is an atheism that understand the diversity of the species and understands that in that vast diversity of life-types there is often no possible reconciliation. Either your fucking someone or your the one getting fucked. Life is a struggle for supremacy between different life-types.â

By AshAndMistyInLove (not verified) on 30 Dec 2009 #permalink

Hmm, yes, that's me alright. Small world. I believe that comment was made to a feminist IIRC. I stand by it.

***There is a recent technique that can measure the myelination (insulation by fat that causes impulses to be conducted more quickly in nerve cells) of various parts of the brain, however, and a study has found increased myelination in the brains of people who perform better on reaction time tests. On the other hand, given that the conduction boost was found in the areas of the brain related to vision, it would be premature to take these results as a confirmation of g as a measure of intelligence. And given the plasticity of the developing brain, it certainly has nothing to say on whether there is a genetic link to performance on these tests.***


Have you seen this twin study 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."

Also, see this paper by Thompson & Gray. 'NEUROBIOLOGY OF INTELLIGENCE: SCIENCE AND ETHICS'

"Linking genes, brain structure and intelligence. a | Genetic influences on intelligence have been assessed directly (top arrow). The consensus of many
studies is that at least 40% of the variability in general cognitive ability (g) can be attributed to genetic factors89. 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% heritable34 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 genes34 (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). To better understand genetic influences on brain structure, correlations are shown for regional grey matter volumes in sets of identical (monozygotic (MZ)) and fraternal (dizygotic (DZ)) twins. These correlations vary across the brain surface (red, highly correlated; blue, less well correlated). The structure of the brains of identical twins is more similar than that of fraternal twins. F, frontal cortex; S/M, primary sensorimotor cortex; W, Wernickeâs area." (page 475)

Anyone who still argues that racial differences in intelligence are not genetic has no respect for science.

A century's worth of intelligence tests has shown a consistent one standard deviation difference between blacks and whites. No combination of non-genetic factors can explain this gap.

So please stop propagating nonsense and accept the evidence.

Dear "John"

So far the most consistent evidence of what you claim has been people like you claiming it again and again and again. This is not impressive.

Observer, have you seen comment #18? John, when did we start being able to quantify prenatal environment in such a way that we can measure how much it correlates with IQ? When did we quantify shared culture and cultural assumptions? I have a great deal of respect for science and the number of things it has yet to uncover for us. Why don't you?

Interesting, I am putting together a fun website which will allow users to test their reaction time - but more importantly, will allow users to see their reaction time against other relative to different scenarios. The data will probably take many months to build. Please take a look and suggest changes you think would be useful.

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I don't think separate groups have been separated long enough for something like intelligence differences between them to have occurred given that such a complex trait.

It amuses and saddens me that there are researchers that spend their whole lives trying to prove difference on something nebulous as race.

I think,in the end,it will be recognised by all that race is a fracked concept and that differences on the basis of race is equally fracked.

And what will be worse is the recognition of the needless suffering that such ideas have caused on this planet.

There is now way that there is a difference more significant between races than within races. Same thing with gender and everything else. We are all human.