Re: Brain size, IQ

Ralph L Holloway (
Tue, 10 Sep 1996 00:01:55 -0400

On 9 Sep 1996, Gerold Firl wrote:

> In article <>, Ralph L Holloway <> writes:
> |> On 5 Sep 1996, Gerold Firl wrote:
> It sort of appears that h. erectus is where a lot of the increase in
> brain size occurred; if habilus reached 700 cc, then that's where
> erectus started (according to my model of evolutionary transitions).
> Erectus would then span 700 cc to 1200 cc.

Yes, I would agree, and that is why some really secure postcranial remains
of whatever the habilines were would be of such great interest. Again, if
one uses KNM-ER 1470 as a habiline, then there is some suggestion from
femoral remains that its stature and probably body size was close to our
own, in which case our encephalization is considerably higher (that it is
higher seems certain, but by how much is not certain). If OH62 is the
habiline we are thinking about, then the increase in brain size to an
erectus hominid involved both allometry and isometry. And if by erectus
times the body size has not increased very much, most of the increase in
brain size is purely related to the brain and not the body as some kind of
allometric tag-along.

> |> OK, but remember that the total evolutionary trajectory in hominid brain
> |> brain size from early Australopithecus to Homo sapiens was about 1000 ml,
> |> i.e., from about 450 to 1450ml. That is just about the same as the range
> |> of normal variation in modern H. sapien's brain size, i.e., from about 900
> |> to 2000, with very little demonstrable evidence for differences in
> |> "intelligence" (except perhaps as measured by IQ scores, which I really
> |> don't know what these tests measurethat might have been of survival value
> |> during the Pleistocene).
> That is interesting, but obviously the span of intelligence between
> the average australopithicus and the average modern human is greater
> than the within-species range currently ... right?

My point here is abit opaque, I think. When we talk about the increase in
brain size in the fossil record, we ASSUME increases in intelligence, or
cortically-mediated adaptive behavior accompanied those changes in brain
size. But the units themselves, i.e., volume or weights in cc's, ml's, or
grams, are showing no significant relationship to behavior within our
species. How can we legitimately use those units to discuss
brain-size-intelligence interrelationships in the fossil record? If we do,
are we not then more or less hoisted on our own petards to ascribe the
variation in modern human species' brain weights along the same lines?
Certainly Rushton does, and several others. But I am skeptical of this,
and that is why I am always interested in the organization of the brain as
well as its size. Minor differences in our brain sizes seem to have little
if anything to do with intelligence as far as I can tell. From Australian
Aboriginals to Aleut Eskimos, all groups are, in my mind at least, coping
well with their environments and their adaptations prior to European
contact were surely adequate if not also optimal. How then can we take
these units, ml's, and use them to discuss measureable changes in
intelligence from one fossil hominid group to another? Are the units
compatible with such attempts? I frankly don't know, but suspect in some
cases you can use this reasoning and at other times you can't, which is a
real pisser for those who want consistency, but then I doubt that
evolution "gives a damn" about consistency.

> And IQ tests, for all their shortcomings, do measure learning ability,
> to some extent. That will have had survival value throughout the
> hominid past.

I don't truly know what IQ measures, and I am leary about homologizing
them or IQ to those behaviors having survival value in the hominid past.

> |> The next question: should the relationship be
> |> studied...?
> The relationship between intelligence and physical characteristics of
> the brain? Surely that should be studied.

Well, I certainly agree, but political correctness does make it difficult
to do so, particularly when human biological ("racial") and sexual
variation become parts of the methodology.
I'm still getting mauled for publishing results that suggested that males
have relatively smaller corpora callosa than females, and that females
brains have more interhemispheric connections. About this, I could be
quite wrong, but why must I be mauled about it?
> |> > I have also read that modern east asian populations have the highest
> |> > cranial capacity/body mass ratio among current humans, and they also
> |> > have the highest IQ's. The possibility of a causal link can not be
> |> > ruled out.
> |> I agree the possible causal link cannot be ruled out entirely, but other
> |> interpretations of the high Asian IQ exist which suggest cultural
> |> mechanisms rather than brain size might be operative, manifested as a
> |> genuine respect for education (not genetically linked as of yet...).
> Quite right. Our understanding of neurophysiology and cognitive
> development is way too primitive to answer such questions in a
> definitive way as of yet. I can see it going either way.
> Consider this, however; if the east asian human subspecies *were* to
> occupy an ecological niche (both inter and intra-species) which
> exploited high intelligence as a competitive advantage, it should be
> expected that their culture would evolve in such a way as to emphasize
> and accentuate those areas of specialization. East asian cultures
> value intelligence, but this can be viewed as a co-evolved reinforcer
> of a biological adaptation for the same trait, rather than as either a
> cause *or* an effect.

If you can demonstrate this more power to you, but I think it will be
incredibly difficult to do so. I would ask, for example, from somewhat
really familiar with the history of East Asian societies whether learning
and education have always been valued. I rather doubt it.

Ralph Holloway