# Cranial Size and Intelligence Link

1. Sep 7, 2004

### BlackVision

Even though I and others have expressed that there was nothing wrong with the original "Cranial Sizes Between Races" thread as it was completely scientific in nature, I will revise it for this thread and meet Monique's questionable demand as this is a very important issue.

The cranial size and intelligence link have been substantiated by countless mainstream journals such as Intelligence and the American Journal of Psychiatry. Even Evo should be able to state these are reliable sources. If there is a study in any of the mainstream journals that state the contrary, I am unaware of them. So any thoughts to this? Agree? Disagree?

Some excerpts:

"We now know quite conclusively from MRI studies, for example, that IQ is correlated with brain size, but we still don't know what precisely it is about brain size that causes this correlation."--Kings of Men: Introduction to a Special Issue of the Journal of INTELLIGENCE (1998)
by DOUGLAS K. DETTERMAN (kudos to Mandrake for this one)

"The first of these MRI studies were published in the late 1980s and early 1990s in leading, refereed, mainstream journals like Intelligence (Willerman et al., 1991) and the American Journal of Psychiatry (Andreasen et al., 1993). I know Gould is aware of them because my colleagues and I routinely sent him copies as they appeared and asked him what he thought! For the record, let it be known that Gould did not reply to the missives regarding the published scientific data that destroyed the central thesis of his first edition."--J Ruston

"The published research that most clearly shows the correlation between brain size and intelligence employed MRI, which creates, in vivo, a three-dimensional image of the brain. An overall correlation of 0.44 was found between MRI-measured-brain-size and IQ in 8 separate studies with a total sample size of 381 non-clinical adults. This correlation is about as strong as the relationship between socioeconomic status of origin and IQ. In seven MRI studies of clinical adults (N = 312) the overall correlation was 0.24; in 15 studies using external head measurements with adults (N = 6,437) the overall correlation was 0.15, and in 17 studies using external head measurements with children and adolescents (N = 45,056) the overall correlation was 0.21. The head size and brain size correlation with the g factor itself, which Gould would have you believe is a mere artifact, is even larger --- 0.60! (Jensen, 1994; Wickett et al., 1996).

"Is it reasonable to expect that brain size and cognitive ability are related? Yes! Haug (1987, p.135) found a correlation of 0.479 (N = 81, P<0.001) between number of cortical neurons (based on a partial count of representative areas of the brain) and brain size in humans. His sample included both men and women. The regression relating the two measures is: number of cortical neurons (in billions)= 5.583 + 0.006 (cm3 brain volume). According to this equation, a person with a brain size of 1,400 cm3 has, on average, 600 million fewer cortical neurons than an individual with a brain size of 1,500 cm3. The difference between the low end of the normal distribution (1,000 cm3) and the high end (1,700 cm3) works out to be 4.2 billion neurons. That amounts to 27% more neurons for a 41% increase in brain size. The best estimate is that the human brain contains about 100 billion (1011) neurons classifiable into perhaps as many as 10,000 different types resulting in 100,000 billion synapses (Kandel, 1991). Even storing information at the low average rate of one bit per synapse, which would require two levels of synaptic activity (high or low/on or off), the structure as a whole would generate 1014 bits of information. Contemporary supercomputers, by comparison, typically have a memory of about 109 bits."--J Rushton

2. Sep 7, 2004

### humanino

I still don't understand. Why is this not flawed ? IQ and crane size are related OK nobody doubts. This teach us nothing. Try to correlate crane size with income.

3. Sep 7, 2004

### Phobos

Staff Emeritus
Correlation coefficients of 0.44, 0.25, 0.15, & 0.479 are terrible and, to me, indicate no correlation at all. Maybe if the correlations were 0.7 or higher, then you would have something to talk about.

Plus, I have yet to hear about a reliable way to quantify IQ.

4. Sep 7, 2004

### BlackVision

In terms of g the correlation was found to be .60. But I believe it would be a mistake to dismiss even a .25 correlation so quickly.

And no correlation at all would be 0.00 not 0.25, 0.44, etc.

5. Sep 7, 2004

### humanino

Please, could someone explain to me where I am wrong.

You see a correlation between IQ and crane size. I feel this is because those two features are correlated to another more significant one, such as income, or general level of life. That is, somebody with an easier life will both have a larger crane, and a higher IQ. That would clarify everything to me as far as I understand. But everybody seem to ignore my posts, as if I was either totally ununderstandable, or totally non-sens.

6. Sep 7, 2004

### Phobos

Staff Emeritus
Hi humanino. Be patient. You're probably not being ignored, there's just a lot of posts for people to respond to here at Physics Forums.

I am not convinced that there is a simple & direct correlation between brain size & IQ. They may be somewhat correlated, but life is more complicated then that.

For what its worth, Neandertals had larger brains than H. sapeins but their technology (a possible indicator of IQ) was not as advanced as ours.

7. Sep 7, 2004

### Phobos

Staff Emeritus
Yes, 0 = absolutely no correlation at all, but even random variations can do better than 0.

0.25-0.44 seems to be a very weak correlation and indicates that there are other significant factors involved.

In many other areas of science, I would be inclined to dismiss a correlation of 0.25 (that's getting down into random noise). Getting closer to 0.5 is more interesting, but still indicates that the majority of the contributing factor is missing from the equation.

0.6 is better. Remind me what the g factor is.

A "good" correlation coefficient depends on the type of work. For environmental sampling, reaching 0.7 or higher might be needed for a rating of "good". For some chemical studies, the scientist might demand greater than 0.9. I'm not familiar with what psychiatrists would consider to be good. Perhaps its lower given the complexities of the human mind.

8. Sep 7, 2004

### humanino

I was also afraid that because of my offending post in the previous similar thread (where I commited a personal attack : I was obviously provocating in response to what seemed to me a provocation) people would not read my posts anymore in the biology forum.

I also doubt at all on the significance of IQ tests. I do very well at those (I could easily afford Mensa, but that appear to me as an horrible form of racism, and the people I met there were simply... frustrated), but I think it just measures your ability to conform to normal-thinking. For instance, it does not take into account emotion/sensitivity. A friend of mine which is really clever like to find another logical answer (one not in the list) This is way funnier as well as way more difficult : it requires both logic and imagination.

So IQ does not measure anything anyway.

9. Sep 7, 2004

The reliabilities (accuracies) of IQ tests

• Degree of agreement can be quantified by the correlation between different observers or between repeated measurements by the same observer. When a correlation coefficient is used this way, it is termed a reliability coefficient, symbolized r$_{xx}$. The difference between the reliability coefficient and unity (i.e., 1 - r$_{xx}$) represents the proportion of the total variance of the measurements that is attributed to measurement error.

It is a common misconception that psychological measurements of human abilities are generally more prone to error or inaccuracy than are physical measurements. In most psychological research, and especially in psychometrics, this kind of measurement error is practically negligible. If need be, and with proper care, the error variance can usually be made vanishingly small. In my laboratory, for example, we have been able to measure such variables as memory span, flicker-fusion frequency (a sensory threshold), and reaction time (RT) with reliability coefficients greater than .99 (that is, less than 1 percent of the variance in RT is due to errors of measurement). The reliability coefficients for multi-item tests of more complex mental processes, such as measured by typical IQ tests, are generally about .90 to .95. This is higher than the reliability of people's height and weight measured in a doctor's office! The reliability coefficients of blood pressure measurements, blood cholesterol level, and diagnosis based on chest X-rays are typically around .50.
(Arthur Jensen. The g Factor. p50.)

Validity and reliability being statistical concepts that are distinct from one another, if you meant valid when you said reliable please specify that.

Last edited: Sep 7, 2004
10. Sep 7, 2004

### Staff: Mentor

I also see the usual problems with meta-studies...

11. Sep 7, 2004

What g is, again

The g factor is the principal statistical component common to multiple cognitive tests of ability. It provides IQ scores with all of their practical validity, such that an IQ score is only worthwhile as a predictor of success in any cognitively demanding domain as far as it is loaded on the g factor.

• ...g is the sine qua non of test validity. The removal of g (by statistical regression) from any psychometric test or battery, leaving only group factors and specificity, absolutely destroys their practical validity....
(Arthur Jensen. The g Factor. p270.)

Last edited: Sep 7, 2004
12. Sep 7, 2004

### humanino

I swear I have very good results at IQ tests, partly because I have done many. Yet, I have very few doubts that my mental ability is not abnormaly high. I am a PhD student, so I am not totally dumb, but I am sure not a genius. Just contemplate my poor english. I know several persons who have relatively bad results at IQ tests, yet they are really interesting persons : they have quite a cultural-luggage, and also have other skills such as playing and composing music as a miracle. They do not either exhibit an especially slow mind.

I really don't understand this g factor unfortunately. Maybe the tests I had are not good tests. Yet I know they are standard to this Mensa association.

13. Sep 7, 2004

### humanino

Let us accept this g factor as an objective measure of intelligence. What about my other objection : I am ready to accept that crane size and intelligence can be related (even though this is not obvious, and Neandertals had larger brains), due to ease of life as explained earlier.

You could find correlations between the size of the vehicle and the size of the house : both are just the result of income.

14. Sep 7, 2004

### Monique

Staff Emeritus
Just curious :) what do you study?

15. Sep 7, 2004

### humanino

this is boring...

It is unfortunately classified in nuclear physics, which leads everybody to think about weapons and nuclear plants. :grumpy:

I am studying the structure of the proton, made up of three quarks. The usual nuclear energy we use today is the residual interaction between protons and neutrons, as the chemical interaction is a residual electromagnetic interaction between neutral systems. The fact that those interactions are residual causes the energy to be weak as well as the process to be dirty (they produce wastes). Electrical energy does not by itself create significant polution for instance. The true interaction is "Chromodynamics" and I am glad to study such a beautifully named theory

We might hope that, far in the future, we will be able to have a clean and much more efficient source of energy. Of course, for political reasons, as well as probably social choices, we want to consume energy right now, not wait another 50 or 200 years. In turn, that could also be used to build new weapons, but we already have enough to destroy the planet like a hundred times anyway (that is 99 times to much ), and also biologic weapons appear way more dangerous to me.

There are even people who argue that we could extract an infinite quantity of energy from the vacuum. This is not very well accepted.

Having a new source of energy is required for the exploration of the cosmos, since carrying fuel is a very bad idea. In the very long term, humanity will eventually have to escape its birth planet (if we manage to deal with polution and we don't blow ourselves), because the sun as you know will expand in a red giant and burn our planet.

Did I already wrote all these lines Sorry, I could speak about that forever :shy:

What do you study Monique ? Are you torturing mice :tongue:

16. Sep 7, 2004

### Phobos

Staff Emeritus

Yes, "valid" sounds more like what I meant rather than "reliable". I was thinking in terms of accuracy, not precision.

17. Sep 7, 2004

### Monique

Staff Emeritus
that all sounds very interesting, ofcourse it would be off-topic to go into that
I don't torture mice :)

18. Sep 7, 2004

### humanino

So what do you study ? Maybe you already said that somewhere else, if you remember you could just post the link. Or maybe your studies are even more secrety than mines

19. Sep 7, 2004

### Monique

Staff Emeritus
It's in my profile medical biochemistry, involving molecular biology and genetics.

20. Sep 7, 2004

### BlackVision

Homosexuality is said to have a 0.5 correlation and it seems evident that genetics plays a considerable role in one being homosexual. At least to me it does.