Re: Brain Development

Ralph L Holloway (rlh2@COLUMBIA.EDU)
Tue, 7 Feb 1995 10:58:00 -0500

A couple of points regarding Bonnie's post. There isn't enough
information to be completely certain about body weights in earlier
hominids. The Nariokotome H. erectus youth is about the same as modern
Homo in skeletal size, and therefore one assumes body weight, but its
brain was about 900 cc. So from H. erectus on ( and we should also
consider the Javanese specimens) body size is pretty constant and brain
size increases from roughly 800-850 as an average to about 1300 in less
than a million years.That's about 1/2 of the total increase in cranial
capacity since australopithecines ( well, more or less). Habiline fossils
are terribly difficult regarding body weights. OH 62 is tiny (as was OH
8), and OH 13 24 16 and OH 7 are anybody's guesstimates. Yes brain size
is probably upward of 600-650 cc. Were these smaller than A. africanus,
with an average of about 450 cc? As I have published several times,
increases in brain and body weights are not always connected, and the
same was shown for the horse lineage millions of years ago (See Tilly
Edinger's 1948 (?) Evolution of the Horse brain publication.) There are
mosaics within the mosaic of evolution. Trying to get these to match
behavioral complexity, "intelligence", etc., is fun, but its just that at
the present time.
As for the different lobes, wow, are we suffering from an
embarrassment of poor evidence. Aside from primary visual cortex and
posterial parietal association cortex, all dependent on demonstrating the
goddamn lunate sulcus, we can say nothing accurate about different lobe
size changes in hominid evolution. I am still getting manuscripts saying
that Neandertal's had tiny frontal lobes, or even prefrontal lobes, when
from monekeys through humans, the frontal lobe is about the same relative
size. The slope is usually around 1.09 when you plot prefrontal cortex
against volume of brain or cortex, and the difdferent primate points lie
very much on the same line.
Ralph Holloway.
On Tue, 7 Feb 1995, Bonnie Blackwell, x 3332

> actually, many large mammal families do show rapid speciation during the
> last 5 My. some also show some moderate increases in brain size, but
> when compared to body weight, this is negligible. one thing that many
> families show during this period is the general increase in body size.
> hominids here are no exception, going from 1.25 m average height
> (and ~~ 40-50 kg??) to our current 1.75 m. it is not so much the size of
> the brain that is of interest here, but the greater development of certain
> areas such as the frontal lobes, speech centres, etc.
> b
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Bonnie Blackwell,
> Dept of Geology, (718) 997-3332
> Queens College, City University of New York, fax: 997-3349
> Flushing, NY 11367-1597