Re: Brain size, IQ

Gerold Firl (
3 Sep 1996 21:06:02 GMT

In article <>, (Len Piotrowski) writes:
|> In article <50565o$> (Gerold Firl) writes:

|> >The june 83 issue of scientific american has an article on homo erectus
|> >remains found in zhoukoudian cave by wu rukang and lin shenglong, which
|> >shows the steady increase in cranial capacity during the 230,000 years
|> >over which the cave was occupied. The earliest skull was about 500,000
|> >years old, with a capacity of 915 cc, while the latest was 1140 cc from
|> >about 230,000 bp.

|> Homo erectus hasn't been included with modern humans, as far as I am aware,
|> regardless of any trends in brain size from Chinese sites. Despite being
|> tangential to the current discussion, I would also question the applicability
|> of physical data from one region's sites to an entire species and subsequent
|> evolutionary events!

I used that data because I happened to have it on hand. The trend is
present for all the hominid species: cranial capacity increases with
time. Archaic h. sapiens had a cranial capacity of about 1200 cc, just
like late-model h. erectus. That has increased 25% to the modern size
of 1500 cc over the last 200,000 years or so. (This is from memory, so
my numbers are a little vague.)

This trend is clearest for erectus, which started with a much smaller
brain; I believe early versions weighed-in at around 700 cc. You had
claimed that cranial capacity did not increase over time within a
single species; I was pointing out that you are misinformed. The data
from zhoukoudian actually understates the magnitude of the trend, since
erectus spanned about a million years.

You're awfully quick to dispute things, lenny, even when you know
nothing about the subject. This isn't tangential to the discussion,
since cranial capacity clearly *is* a heritable trait, and furthermore
it is also clearly correlated with the long-term increase in hominid

You wrote:

|> >|> Well, if head size is correlated with brain size (which you may not be ready
|> >|> to concede) then the only significant differences in head size resolved by the
|> >|> fossil record are at speciation events. In between those episodes there
|> >|> appears to be no significant "heritability" of head size in the record.
|> >|> Perhaps you can clarify this anomalous situation?

|> >No anomaly - you are simply misinformed. Cranial capacity does not
|> >suddenly "jump" at "speciation events" - what's more, there are no
|> >speciation events.

|> Double boggle!

You sure boggle a lot.

|> >Biological evolution moves much more gradually than
|> >that. On a geological time scale, species can appear very suddenly,

|> No felt contradiction in this statement, Firl?

None whatsoever, lenny. If the fossil record provides samples at
million-year intervals, then it will appear that new species develop
very suddenly. You need to understand the difference in scale between a
20 year generation time and the million year speciation time constant.
(hominid species seem to show an approximate million year time
constant, going from australopithicus to habilus to erectus to sapiens)
Nothing much happens in a single generation, but over the course of a
large number of generations (a few thousand?) a new species can appear.

Getting back to your claim that cranial capacity is not a hereditable
trait, and all boggles aside, there is no anomaly: human intelligence
is adaptive, and natural selection has produced successivly more
intelligent humans. It has also produced larger brains.

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