Re: Brain size, IQ

Gerold Firl (geroldf@sdd.hp.com)
29 Aug 1996 22:38:48 GMT

In article <lpiotrow.387.322465BB@magnus.acs.ohio-state.edu>, lpiotrow@magnus.acs.ohio-state.edu (Len Piotrowski) writes:

|> In article <501g5s$1q5u@argo.unm.edu> mycol1@unm.edu (Bryant) writes:

|> >I don't recall the cubic centimeters, but do seem to recall some
|> >substantial growth in cranial capacity since H. erectus.

|> Not since H. erectus, as far as I am aware, unless you are including H.
|> erectus in the statistic. Do you have some data that shows this trend?

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.

I don't have comparable data for h. sapiens, but I would expect similar
trends. (Modern cranial capacity is around 1500 cc)

There is no distinct boundary between h. erectus and h. sap, whatever
your semiological evidence to the contrary. Archaic h. sapiens looks
just like late h. erectus, and vice versa. I would expect cranial
capacity of h. sap to have increased from approcimately 1200 cc 150,000
years ago to the present 1500.

|> 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. Biological evolution moves much more gradually than
that. On a geological time scale, species can appear very suddenly, but
as eldridge has demonstrated, there _are_ intermediate forms. Given the
paucity of the fossil record, there may appear to be discrete events,
but at finer levels of discrimination evolution proceeds one mutation
at a time.

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