brain size -intelligence

Thu, 20 Oct 1994 18:48:00 PDT

Let me use the occasion of a comment by Herdrich to make a few observations
that are not directed at him, but to a variety of posts that make similar
arguments. Herdrich writes:

"I think John Wingards point that a smaller brain can be more
intelligent than a larger one completely destroys Rushton's hypothesis."

While I sympathize with the goal and interest in demonstrating that Rushton
is wrong in his pronouncements, counter arguments need to be solid and not
themselves demonstrably unacceptable. For example, Michael Lieber nicely
pointed out the difficulty in linking a "gene" with a measurement on a
person--alleles produce proteins, proteins enter into various biochemical
pathways, these in turn have their own products which further affect and
interact with other products, etc. As several have already noted,
however, his comments in effect deny the validity of indirect methods of
demonstrating linkages; e.g., the linkage between smoking and lung cancer was
not arrived at first by demonstrating the biochemical pathways and biological
responses involved, but by studies of association which eliminated other
potential causes of lung cancer and left smoking as a common denominator for
a large number of cases of lung cancer. Genetic linkages are validly made
even when the the actual linkage between allele and trait is poorly

In the above quote the single counterexample is taken as demolishing the
purported association. But statistical analysis is based on pattern that is
established in the aggregate, not on individual cases. Translate the
argument to another domain: women, on the average are not as tall as men.
But, the doubter retorts, I know a woman who is taller than a man--therefore
the claimed difference is not valid.

The variant on the single counter example, namely that
there is no association between brain size and "intelligence", is tricky
because it is clearly not true when we consider not the range of human brain
size variation, but throw in brain primate brain sizes as well. Humans are
clearly smarter than primates with regard to a range of capacities that we
use to distinguish ourselves from other primates and it seems reasonable to
conclude that this difference relates to the fact that we have big brains.
Or throw out humans entirely and consider the encephalization that has taken
place as you go from mammals to primates and the fact that primates,
generally speaker, seem to be smarter than mammals. Over large ranges,
clearly there is an association between brain size and "intelligence." Put
the argument into a different context. In humans there is a correlation
between height and weight. The strength of that correlation does depend,
however, on the range of data considered. THat is, if you only sample people
between, say 5' and 5' 1" tall and measure the correlation between height and
weight you will get a low correlation coefficient whereas if you consider all
heights you will get a high correlation. In other words, is there NO
correlation between brain size and "intelligence" or is it the case that over
the range of brain sizes typified by our species, the range in variation in
intelligence for any given brain size is large in comparison to the variation
in brain size? Data would be helpful.

Mike Salovesh (sorry for the possible misspelling) seems to use the "lets
recast the argument in a (distorted) extreme form and now show the argument
invalid." He seems to argue that since historically we know there was
contact among Africa, Asia and Europe, that these three regions were not
"isolated" and hence no "pure races" existed, hence there are no races, etc.
Are the gene pools (the gene pool includes not just what alleles are
present, but their frequency as well) essentially identical in these three
areas? Clearly not, hence there has been isolation that allows for genetic
differentiation (and within these areas there is isolation that allow for
genetic differention at even, say, the village level). "Genetic isolation"
does not mean "total isolation," but limitation in gene flow. If individuals
in group A are more likely to mate with individuals in group A than with
individuals in group B, then the necessary condition for differentiation
through isolation exists. Clearly, members of a breeding population in
central china are not very likely to breed with members of a breeding
population in central africa or in central europe and vice versa, hence
differentiation via natural selection (or other evolutionary forces) can/will
take place.

Certainly muddying, if not obfuscating, much of this discussion and attempt
to refute Rushton, is, I think, an implicit acceptance of his use of racial
classification (whether or not that classification is faulty) as a relevant
dimension for measuring a trait. Suppose (for the sake of argument) that you
want to measure the correlation between brain volume and some purported
measure of intelligence. Why begin with a subdivision of the species using a
classification that has nothing to do
with the hypothesis, UNLESS ONE'S MOTIVATION <<IS>> RACISM? For example,
would one have initially studied the relationship between smoking and lung
cancer by FIRST dividing the sample according to one's ancestry?
In the absence of an a priori reason for relating ancestry to the
relationship, obviously not. So if your goal is to relate some measure of
intelligence to brain volume, you would begin by looking at a some sample of
persons, regardless of ancestry to see if there is or is not an association
between brain size and the measure of intelligence.

Suppose, for the sake of argument, that you did this study and discovered a
positive correlation and suppose you now linked this to the asserted
difference in brain size by region of origin. So what? What have you
established? Put it into another way. Why does this become contentious, as
it obviously does? In other contexts, exactly this kind of study is done
without contention. For example. Initial studies established an association
between birth weight and risk of death of the neonate. [This is a standard
classroom example of stabilizing selection as both low weight and high weight
babies are at greater risk.] Subsequent studies have shown that the average
birth weight is not constant but varies by ethnicity. The same kind of
argument, yet it does not casue an uproar--rather it has led to research into
why there should be differences in birth weight.

Cleary, a major difference is that intelligence is not seen neutrally, but
has been central to emic notions of self vis a vis others. Futher, we seem
to have, in our culture, the idea that difference = inequality. That is, if
we culturally define a difference we also map onto that difference an
inequality relationship. Women <> men, therefore one must be superior.
Bosses and workers are not the same, therefore one must be superior. My
religion is not the same as your religion, therefore my religion must be
superior. One way to escape from the hierarchical imposition is to deny the
difference. If women and men are identical then the superior/inferior
mapping cannot be applied.

If this is the case--that as part of our cultural baggage we impose hierarcy
when we culturally recognize difference--then we are in something of a
quandry. We rightly deny the hierarchy, but our culture then forces us to
deny that there is difference and this leads into unsustainable arguments
from an etic perspective. To me, the answer to Rushton is not to engage him
on arguments about the data per se, but to challenge him on what the data
ALL ABOUT? I am not any better or worse a person by virtue of being member of
a breeding popuation which has different allele frequencies than does another
breeding population. I have Scottish ancestry and if it is shown that Scots
have, on the average, the smallest brains of any group and their intelligence
on the average, would make sloths look smart, so what?

What interests me is not whether group A is or is not "smarter" on the
average than group B by virtue of having different allele frequencies, but
how does the brain work? How is it possible to have a brain that can do what
any member of the species Homo sapiens can do so easily--see things, hear
things, talk, reason etc. What is consciousness? Why would selection
select for consciousness? What made us "smarter" than other species? How
does the brain so easily learn a language? These, and questions like these,
are the challenging and intellectaully exciting questions--not what group has
the biggest brain on the average.

D. Read