Brain size, IQ 
Author Message
 Brain size, IQ


>>>>As Dawkins points out in his _Extended Phenotype_, the association of
>>>>larger cranial capacity and apparently increased intelligence in the Homo
>>>>lineage suggests (demands) heritability for brain size in past human and
>>>>proto-human populations.  This is, hopefully, not controversial.
>This is only a bit contriversial in that the cranial capacity is not the
>ultimate gauge of "intelligence".  Apparently the frontal lobes act as "super
>chargers" for certain brain activities which are typically included in the
>tests for "intelligence".  For instance, the Neanderthal had a significant
>cranial chamber; however, it was full of cerebellum and temp{*filter*}lobes.  This
>indicated a human with incredible coordination and reflexes.  Unfortunately,
>these aspects are not necessary for a high score on I.Q. tests.

I see this minor point of controversy as all the world. Brain size is not as
important a factor in the development of modern human behavior as the capacity
to  restructure and reorganize brain functions. The apparent emphasis on
coordination, reflexes, and handedness of Neanderthals suggests a
co-development in those areas of the brain associated with language. The
significant physical differences between H. sapiens neanderthalensis and
H.s.s. in the mechanisms of speech production seem to parallel a significant
reorganization of the brain as well, perhaps to purposefully control speech.
This may have resulted from the evolution of a capacity of the brain to
re-organize control of behavior beginning with the Neanderthals in the first

>>What's controversial about the notion that cranial capacity was heritable
>>during human evolution?  How else do you explain the dramatic changes in
>>head size through time, as evidenced in the fossil record of our ancestors?
>Cranial capacity is sort of equivalent to RAM memory in your computer.  It
>doesn't mean much if your running a 286 with windows 3.0.  The idea that
>evolution is creating a "meaner-leaner-brain" is true.  It may be limited by
>biochemical {*filter*}-sugar factors involving metabolism, so we can't get too
>e{*filter*}d for our genius children - they may all wind up diabetic if they get
>too smart.

I am skeptical of the proposed value of sugar to the evolution and
development of brain function. At any rate, the brain is *not* equivalent to
RAM memory. There are no control networks, no feedback loops, no comparator
mechanisms, no differentiated structures that make RAM think or process
information or negotiate between states and values. You may argue that it
holds "software" that does that, but it can hold "software" until the plug is
pulled and it won't think. Software are instructions, but instructions won't
do anything on their own. Until other organized structures intervene to
execute them, nothing happens. The brain, on the other hand, is a patently
different kind of mechanism.

>The girls develop faster than the boys, initially, when considered as two

"Develop" is a loaded term. Girls maintain a particular early form of
head-and-body ratio through much of their early growth spurt.

>This is primarily due to the process of masculinization during
>childhood from age six through puberty.  

More generally, maturation brings to an end both growth and development in
boys and girls, but not in the same way or on the same schedule.

>After that, the boys rush ahead.  
>Remember, this does not apply to any particular man or woman.  Many women are
>so smart that they out think most men.

As a result, girls maintain their neotenic features late into their
development, a characteristic that would apparently contribute to an
extended period of complex learning and brain re-organization.

>>I don't follow this.  Sorry. Could you reword this?  
>I agree with Bryant, you should reword your paragraph.

This was answered in a previous post, and see above.



Sat, 20 Feb 1999 03:00:00 GMT
 Brain size, IQ

     I guess I've missed some of the earlier discussions of brain size. I
notice from the previous post that there is a claim that Neandertals,
while having large brains, had relatively small frontal lobes, and a lot
of cerebellum, etc. This is sheer nonsense. The more sloping frontal of
Neandertals is not an indication of the size of the frontal lobe of the
Neandertal brain. The frontal lobe is about 38% of the cerebrum in modern
humans, chimps, and surely, Neandertals. The cerebellar lobes are not
relatively larger in Neandertals than in modern Homo sapiens. Aside from
shape differences of the brain endocasts, I haven't been able to identify
any "primitive" characteristics in Neandertal brain casts.
R. Holloway

Sat, 20 Feb 1999 03:00:00 GMT
 [ 2 post ] 

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