Why do people care about brain size?

[ShawnD]

In the thread about racists, it was said that research has been done by racists to prove that africans have smaller brains.

What I'm wondering is why anybody would care. From what I've seen, bigger brain doesn't seem to make people smarter at all. The smartest people I've ever known were always small people who would presumably have smaller brains. The smart people I associate(d) with do not follow any sort of pattern when it comes to head size. My high school chem teacher was very smart and he had a small head. My high school physics teacher had a master's degree in physics and spoke 4 languages; he had a big head. In my current school, some of the engineering profs have big heads, some have small heads.
From what I have seen, head/brain size do not affect intelligence at all.

Why would anybody care if africans had bigger or smaller brains?

 

[chroot]

Well, evolutionarily speaking, brain volume is a good way to measure a species' average intelligence. In other words, people are smarter than dogs, in large part because we simply have more gray matter.

It certainly can't be used as an indicator of an individual's intelligence, or even that of a small subgroup.

- Warren

 

[Ivan Seeking]

Isn't the ratio of brain to body weight still considered a good indicator of average intelligence?

 

[Njorl]

A large brain will have greater separation of the critical neurons. This greatly eases their attachement while emplanting a human brain in a gorilla body, or a fusion-powered, super cyborg warrior.

Njorl

 

[Monique]

Isn't the ratio of brain to body weight still considered a good indicator of average intelligence?

I believe it is called (en)cephelization or something.. some time ago someone asked this question..

 

[Moonbear]

Those who are worried about brain size are small-minded people. You are right, brain size, at least within the variation we're talking about in the adult human population, has nothing to do with intelligence. There are known differences between the size of specific brain regions in men and women...these are known as sexually dimorphic nuclei. However, these have nothing to do with intelligence, but instead control, mainly, reproductive functions. So, naturally these parts of the brain need to be different because they are controlling different reproductive systems.

Interestingly, there's a recent report out that both supports that there are populations of people with lower intelligence, and at the same time, debunks that it's not related to racial/genetic differences. In fact, what the study has identified is that in many developing nations, there are widespread vitamin deficiencies in the population. It's the nutritional deficiencies that are hindering normal development and leading to suppressed mental functioning. Since some of these deficiencies have affected development since birth or early childhood, simply supplementing vitamins in adults won't likely do anything, but providing supplements to the pregnant women and throughout childhood should help the next generations vastly improve compared to the current generation.

What is interesting to me about this study is that it focused on developing nations. I wonder if anyone has looked at vitamin deficiencies among the poor in developed nations, such as the U.S., where hunger is still prevalent and where there are still huge disparities in school performance between socioeconomic populations. It's usually attributed to lack of funds for school supplies or lack of sufficient teachers or social factors that don't reinforce education as a priority, but could it be something so simple as a nutritional influence?

 

[ShawnD]

That's an interesting theory. Now we need to introduce the guns for vitamins program

 

[loseyourname]

China has a huge iodine deficiency problem and by far the larger proportions of cretins of any nation in the world because of it. They really don't need supplements, at least not for this. All they need is iodized salt or more seafood in their diet.

 

[hitssquad]

people are smarter than dogs, in large part because we simply have more gray matter.

...And in part because humans have a higher ratio of white-matter to gray-matter than do dogs:

• The brain's "gray matter" consists of the unmyelinated cell bodies of the neurons. The "white matter," underlying the cerebral cortex, consists of the cortical neurons' myelinated axons, the association fibers that transmit neurally encoded information (as electrochemical action potentials) from one part of the brain to another and also connect the left and right cerebral hemispheres. The myelin sheath surrounding the nerve fibers acts as an insulator, similar to the insulation on an electrical wire. A large part of the brain, by weight and volume, consists of white matter, or myelinated neurons. Compared to other species, humans have a larger proportion of white matter in relation to cortical gray matter.
  (Arthur R. Jensen. The g Factor. p256.)

It certainly can't be used as an indicator of an individual's intelligence,

Brain size as measured by MRI typically has a Pearson r correlation of +.40 with IQ:

• ...the technology of magnetic resonance imaging (MRI) now makes it possible to obtain a three-dimensional picture of the brain of a living person. A highly accurate measure of total brain volume (or the volume of any particular structure in the brain) can be obtained from the MRI pictures. Such quantitative data are now usually extracted from the MRI pictures by computer.
  
  To date there are eight MRI studies [10] of the correlation between total brain volume and IQ in healthy children and young adults. In every study the correlations are significant and close to +.40 after removing variance due to differences in body size...
  
  Two of the MRI studies used a battery of diverse cognitive tests, which permitted the use of correlated vectors to determine the relationship between the column vector of the various tests' g factor loadings and the column vector of the tests' correlations with total brain volume. In one study, [10f] based on twenty cognitive tests given to forty adult males sibling pairs, these vectors were correlated +.65. In the other study, [10g] based on eleven diverse cognitive tests, the vector of the tests' g loadings were correlated +.51 with the vector of the tests' correlations with total brain volume and +.66 with the vector of the tests' correlations with the volume of the brain's cortical gray matter.
  (Arthur R. Jensen. The g Factor. p147.)

• 10. (a) Andreasen et al., 1993; (b) Egan et al., 1994; (c) Raz Torres, et al., 1993; (d) Wickett at al., 1994; (e) Willerman et al., 1991; (f) Wickett et al., 1996; (g) Schoenemann , 1997.
  (Arthur R. Jensen. The g Factor. p167.)

or even that of a small subgroup.

Jensen says differently that, "head measurements are significantly correlated with IQ for age-matched whites and blacks":

• Implications of Brain Size for IQ Differences. [25] Chapter 6 reviewed the major evidence showing that head measurements and brain size itself are significantly correlated with IQ. The only available correlations for blacks are based on head length, width, and circumference (and cranial capacity estimated by formula from these measurements); as yet there are no reported correlations between IQ and directly measured brain size for blacks. However, the head measurements are significantly correlated with IQ for age-matched whites and blacks, both on raw measurements and on measurements corrected for height and weight, although the correlations are somewhat lower in blacks. Longitudinal data show that the head circumference X IQ correlation significantly increases between ages 4 and 7, and cross-sectional data indicate that the correlation gradually increases up to 15 years of age, by which time the average growth curves for head size and brain size have reached asymptote.
  
  It is especially important to note that for both racial groups the head size X IQ correlation exists within-families as well as between-families, indicating an intrinsic, or functional, relationship, as explained in Chapter 6. Equally important is the fact that within each sex, whites and blacks share precisely one and the same regression line for the regression of head size on IQ. When blacks and whites are perfectly matched for true-score IQ (i.e., IQ corrected for measurement error), either at the black mean or at the white mean, the overall average W-B difference in head circumference is virtually nil, as shown in Table 12.3.
  (Arthur R. Jensen. The g Factor. pp440-441.)

• 25. The information in this section is based on studies by Jensen & Johnson, 1994; and Jensen, 1994f. Information on the brain's growth curve from birth to maturity is given in Harrison et al., 1964, Chapter 19.
  (Arthur R. Jensen. The g Factor. p520.)

References:

• Andreasen N. C., Flaum M., Swayze V. II, O'Leary D. S., Alliger R., Cohen G., Ehrhardt J. & Youh W. T. C. (1993). Intelligence and brain structure in normal individuals. American Journal of Psychiatry, 150, 130-134.
  
  Egan V., Chiswick A., Santosh C., Naidu K., Rimmington. J. E. & Best J. J. K. (1994). Size isn't everything: A study of brain volume, intelligence and auditory evoked potentials. Personality and Individual Differences, 17, 357-367.
  
  Harrison G. A., Weiner J. S., Tanner J. M. & Barnicot N. A. (1964). Human biology: An introduction to human evolution, variation and growth. London: Oxford University Press.
  
  Jensen A. R. (1994f). Psychometric g related to differences in head size. Personality and Individual Differences, 17, 597-606.
  
  Jensen A. R. & Johnson F. W. (1994). Race and sex differences in head size and IQ. Intelligence, 18, 309-333.
  
  Raz N., Torres I. J., Spencer W. D., Millman D., Baertschi J. C. & Sarpel G. (1993). Neuroanatomical correlates of age-sensitive and age-invariant cognitive abilities: An in vivo MRI investigation. Intelligence, 17, 407-422.
  
  Schoenemann P. T. (1997). The evolution of the human brain and its relationship to behavior. Unpublished doctoral dissertation. Berkeley: University of California.
  
  Wickett J. C., Vernon P. A. & Lee D. H. (1994). In vivo brain size, head perimeter, and intelligence in a sample of healthy adult females. Personality and Individual Differences, 16, 831-838.
  
  Wickett J. C., Vernon P. A. & Lee D. H. (1996). General intelligence and brain volume in a sample of healthy adult male siblings. International Journal of Psychology, 31, 238-239. (Abstract).
  
  Willerman L., Rutledge J. N. & Bigler E. D. (1991). In vivo brain size and intelligence. Intelligence, 15, 223-228.

 

[chroot]

Well, shucks. I guess that little bit of political correctness is out the window now.

- Warren

 

[selfAdjoint]

There is also http://www.loni.ucla.edu/~thompson/MEDIA/NN/genetics_article_NN.pdf showing a strong relationship between the amount of frontal gray matter and "g".