Re: Brain size, IQ

Gerold Firl (
9 Sep 1996 20:06:50 GMT

In article <>, Ralph L Holloway <> writes:

|> On 5 Sep 1996, Gerold Firl wrote:

|> > Any idea about pre-h. erectus cranial capacity? How big was an h.
|> > habilus brain?

|> The habilines are a problem, as it is unclear what they include. Is 1470
|> the same taxon as OH62, or OH7, how big was 1590, etc, etc. 1470=752ml
|> (cranial data snipped)
|> I would say, that perhaps 625 would to 680 would be a reasonable span for
|> H. habilis (whatever it is).

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.

|> > Over the long run, it seems like a safe assumption; archaic h. sap
|> > populations of 150,000 b.p. with cranial capacities averaging 1200 cc
|> > were probably less intelligent than modern humans.

|> 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?

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

|> > 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.

|> How can one test these two possible hypotheses and refute one of
|> them, and possibly others?

A difficult research problem, but one which will be facilitated by
modern ease of travel and emigration. There are so many people now who
live outside their home culture that statistically valid samples of
people who live outside the culture of their ancestors should be
availible. If assimilated east asians in the US have IQ scores which
drop down to the level of their neighbors, that would be a strong
indication that culture is more of a causitive factor.

Disclaimer claims dat de claims claimed in dis are de claims of meself,
me, and me alone, so sue us god. I won't tell Bill & Dave if you won't.
=-=-=-=-=-=-=-=-=-=-=-=-=-=---- Gerold Firl @ ..hplabs!hp-sdd!geroldf