Brain size, IQ 
Author Message
 Brain size, IQ

There's been some discussion of IQ on sci.anthropology lately, and I'd
appreciate any feedback from the interested and informed parties about my
questions below.  Thanks.

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.

But considerable controversy has surrounded the suggestion that this is
still true--that human IQ is still heritable, and that it is related to
gross brain size.  One problem for those who would propose a simplistic
brain size/IQ (causal) relationship is that white women's smaller brains
score higher, on average, than black men's larger brains during IQ tests.  

This is, to my knowledge, the only exception to the IQ/brain size rule to be
found in demographic data (as opposed to occassional anecdotal stories about
Einstein's small brain and the like).  I found it described in a recent
paper by Rushton, an advocate of the IQ/brain size connection.  He
described this exception to the rule as a "paradox."

I do not subscribe to the notion that there are inherent differences in
the cognitive potentials of people from different races/populations (this in
fact contradicts my day-to-day experiences with other folks)... but I find the
issue of brain size and intelligence itself to be rather fascinating.  

Could {*filter*}ly dimorphic neuron packing densities account for white women's
apparently higher 'IQ to brain-unit-area' ratio?  How sensitive are neuron
densities to malnutrition during childhood?

Are there differences in the degree of cortical folding in men brains and
women brains, so that white women might "make up" for smaller brains with
equal cortical surface areas?  How canalized ("genetically 'determined'")
are cortical folding patterns?  

Your thoughts and references will sure be appreciated.  Thanks!

Bryant  



Thu, 11 Feb 1999 03:00:00 GMT
 Brain size, IQ

Quote:

>[snip]
>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.

I am not familiar with Dawkin's hypothesis, but you would be mistaken about
the uncontroversialness of your statement. I'm surprised you haven't heard
about Gould's developmental hypothesis and it's (non-functional,
non-adaptionist) effects upon head/body ratios.

Quote:
>But considerable controversy has surrounded the suggestion that this is
>still true--that human IQ is still heritable, and that it is related to
>gross brain size.  One problem for those who would propose a simplistic
>brain size/IQ (causal) relationship is that white women's smaller brains
>score higher, on average, than black men's larger brains during IQ tests.  

The evolutionary significance of altered developmental ratios for humans,
seems to affect the sexes differently. Females appear to experience prolonged
developmental growth with respect to males, thus  apparently increasing the
time and development of the neural net. A byproduct of this developmental
retardation may just be something measurable by the human IQ test. Who knows?

Quote:
>[snipped - sociobiological IQ argument?]

... if so, so what?

Cheers,

--Lenny__



Fri, 12 Feb 1999 03:00:00 GMT
 Brain size, IQ


<snippage>

Quote:
> But considerable controversy has surrounded the suggestion that this is
> still true--that human IQ is still heritable, and that it is related to
> gross brain size.  One problem for those who would propose a simplistic
> brain size/IQ (causal) relationship is that white women's smaller brains
> score higher, on average, than black men's larger brains during IQ tests.  

> This is, to my knowledge, the only exception to the IQ/brain size rule to be
> found in demographic data (as opposed to occassional anecdotal stories about
> Einstein's small brain and the like).  I found it described in a recent
> paper by Rushton, an advocate of the IQ/brain size connection.  He
> described this exception to the rule as a "paradox."

<snippage>

Hi Bryant,

Surely, one must consider total body size when even beginning to think
about brain size and intelligence.  A larger individual of the same
species is likely to have a larger brain simply due to scaling, and total
brain weight/size isn't where the action is for intelligence.  Many areas
of the brain are relegated to non-thought processes, including many areas
of the cortex.  Until the entire brain is mapped out, and cof\gnitive
function is ascribed to certain regions that then may be compared, the
rest is largely fluff (IMO).  

Matt

  ___________________________________________________________

Matt Fraser                          "The Real World is very


                               humans find it necessary to construct
                                     an illusion of reality."

                                         Author Unknown



Fri, 12 Feb 1999 03:00:00 GMT
 Brain size, IQ


Quote:


>>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.

>I am not familiar with Dawkin's hypothesis, but you would be mistaken about
>the uncontroversialness of your statement.

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?

Heritability means, evolutionarily, "not fixed."  That is, genetic or
allelic variability is responsible for phenotypic variability for a given
trait.  Once an allele is fixed in a population, heritability is zero,
because everybody has the same allele for that trait, and phenotypic
variation in that trait cannot be accounted for genetically.

Quote:
>The evolutionary significance of altered developmental ratios for humans,
>seems to affect the sexes differently. Females appear to experience prolonged
>developmental growth with respect to males, thus  apparently increasing the
>time and development of the neural net. A byproduct of this developmental
>retardation may just be something measurable by the human IQ test. Who knows?

I don't follow this.  Sorry. Could you reword this?  

Bryant



Fri, 12 Feb 1999 03:00:00 GMT
 Brain size, IQ

Quote:

>[snip]
>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?

The controversy is over the simple notion that brain size was heritable and
not something else of which head size (and thus brain size) was an effect.

Quote:
>Heritability means, evolutionarily, "not fixed."  That is, genetic or
>allelic variability is responsible for phenotypic variability for a given
>trait.  Once an allele is fixed in a population, heritability is zero,
>because everybody has the same allele for that trait, and phenotypic
>variation in that trait cannot be accounted for genetically.

By this definition, the human brain size can be viewed as relatively "fixed"
since Neanderthal times, and even relatively unvarying before that with Homo
erectus, which by your definition could indicate that brain size was not
"heritable."  I'm sure this is not what you are driving at.

At any rate, if developmental genes are heritable, their affect on phenotypic
variability of other characteristics like the brain could be considerable,
even if those other genetic characteristics were "fixed."

Quote:
>>The evolutionary significance of altered developmental ratios for humans,
>>seems to affect the sexes differently. Females appear to experience prolonged
>>developmental growth with respect to males, thus  apparently increasing the
>>time and development of the neural net. A byproduct of this developmental
>>retardation may just be something measurable by the human IQ test. Who knows?
>I don't follow this.  Sorry. Could you reword this?  

Developmental retardation leads to greater head to body ratio through the
early growth years, contributing to relatively larger brains, and accentuated
cognitive development into the {*filter*}. This developmental process appears to be
extended among female humans.

Cheers,

--Lenny__



Fri, 12 Feb 1999 03:00:00 GMT
 Brain size, IQ



Quote:
>Hi Bryant,

>Surely, one must consider total body size when even beginning to think
>about brain size and intelligence.  A larger individual of the same
>species is likely to have a larger brain simply due to scaling, and total
>brain weight/size isn't where the action is for intelligence.  

Well, I know that Rushton controls for body size in his analyses for this
reason (good point, by the way).  

Quote:
>Many areas
>of the brain are relegated to non-thought processes, including many areas
>of the cortex.  Until the entire brain is mapped out, and cof\gnitive
>function is ascribed to certain regions that then may be compared, the
>rest is largely fluff (IMO).  

Yeah, it's a baby field, alright.  But I've been impressed that even
though this is the case, some gross anatomical trends seem to exist.  
Unusual hemispheric asymmetry (measured w/ MRI), for instance,
corresponds significantly with developmental instability.  

Quote:
>Matt

Bryant


Fri, 12 Feb 1999 03:00:00 GMT
 Brain size, IQ

Quote:



> >Hi Bryant,

> >Surely, one must consider total body size when even beginning to think
> >about brain size and intelligence.  A larger individual of the same
> >species is likely to have a larger brain simply due to scaling, and total
> >brain weight/size isn't where the action is for intelligence.

> Well, I know that Rushton controls for body size in his analyses for this
> reason (good point, by the way).

> >Many areas
> >of the brain are relegated to non-thought processes, including many areas
> >of the cortex.  Until the entire brain is mapped out, and cof\gnitive
> >function is ascribed to certain regions that then may be compared, the
> >rest is largely fluff (IMO).

> Yeah, it's a baby field, alright.  But I've been impressed that even
> though this is the case, some gross anatomical trends seem to exist.
> Unusual hemispheric asymmetry (measured w/ MRI), for instance,
> corresponds significantly with developmental instability.

> >Matt

> BryantBecareful guys elsewise the politicaly correct police will force you to

dance the politically correct polka

Al



Sat, 13 Feb 1999 03:00:00 GMT
 Brain size, IQ


Quote:


>>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?

>The controversy is over the simple notion that brain size was heritable and
>not something else of which head size (and thus brain size) was an effect.

Um, so you believe that Australopithicine brains and Homo sapiens brains
would be the same if subjected to the same set of environemntal effects?  
Why stop there?  Why not posit that plopping a canary brain in a mouse
skull will result in a perfectly mouse-ly brain in the developed {*filter*}?

Quote:
>>Heritability means, evolutionarily, "not fixed."  That is, genetic or
>>allelic variability is responsible for phenotypic variability for a given
>>trait.  Once an allele is fixed in a population, heritability is zero,
>>because everybody has the same allele for that trait, and phenotypic
>>variation in that trait cannot be accounted for genetically.

>By this definition, the human brain size can be viewed as relatively "fixed"
>since Neanderthal times, and even relatively unvarying before that with Homo
>erectus, which by your definition could indicate that brain size was not
>"heritable."  I'm sure this is not what you are driving at.

I don't recall the cubic centimeters, but do seem to recall some
substantial growth in cranial capacity since H. erectus.  My argument was
that brain size was clearly heritable in the evolutionary past, as
demonstrated by the fossil record.  

Quote:
>At any rate, if developmental genes are heritable, their affect on phenotypic
>variability of other characteristics like the brain could be considerable,
>even if those other genetic characteristics were "fixed."

In which case, via pleiotropy, those are also genes "for" whatever brain
characteristics they affect, and brain development is therefore, by
definition, not fixed and species typical.

Quote:
>Cheers,

>--Lenny__

Bryant


Sun, 14 Feb 1999 03:00:00 GMT
 Brain size, IQ


Quote:


>>>The controversy is over the simple notion that brain size was heritable and
>>>not something else of which head size (and thus brain size) was an effect.

>>Um, so you believe that Australopithicine brains and Homo sapiens brains
>>would be the same if subjected to the same set of environemntal effects?

>How ever did you derive from what I said that conclusion???

Because you said that heritability may not have explained the
evolutionary increase in homonid cranial capacity.

Quote:
>>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?

Gotchya. I misread you as meaning to include erectus.

Bryant



Sun, 14 Feb 1999 03:00:00 GMT
 Brain size, IQ

Quote:

>[snip]
>>The controversy is over the simple notion that brain size was heritable and
>>not something else of which head size (and thus brain size) was an effect.
>Um, so you believe that Australopithicine brains and Homo sapiens brains
>would be the same if subjected to the same set of environemntal effects?

How ever did you derive from what I said that conclusion???

Quote:
>Why stop there?  

I didn't even start it!

Quote:
>Why not posit that plopping a canary brain in a mouse
>skull will result in a perfectly mouse-ly brain in the developed {*filter*}?

Quite imaginative, but on point? Perhaps you are implying by this that head
size and brain size aren't correlated?

Quote:
>>>[snip]

>>By this definition, the human brain size can be viewed as relatively "fixed"
>>since Neanderthal times, and even relatively unvarying before that with Homo
>>erectus, which by your definition could indicate that brain size was not
>>"heritable."  I'm sure this is not what you are driving at.
>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?

Quote:
> My argument was
>that brain size was clearly heritable in the evolutionary past, as
>demonstrated by the fossil record.

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?

Quote:
>>At any rate, if developmental genes are heritable, their affect on phenotypic
>>variability of other characteristics like the brain could be considerable,
>>even if those other genetic characteristics were "fixed."
>In which case, via pleiotropy, those are also genes "for" whatever brain
>characteristics they affect, and brain development is therefore, by
>definition, not fixed and species typical.

... which by this "definition" would make "heritability" a signifier without
distinction.  Every trait that was effectively "developmental" would by
this definition be "heritable" via pleiotropy, and thus incapable of
becoming "fixed," unless, of course, all of development became fixed. Perhaps
this is what you originally meant by "brain size was heritable," that is, that
"development was heritable?"

Cheers,

--Lenny__



Sun, 14 Feb 1999 03:00:00 GMT
 Brain size, IQ

Quote:

>[snip]
>>>>The controversy is over the simple notion that brain size was heritable and
>>>>not something else of which head size (and thus brain size) was an effect.

>>>Um, so you believe that Australopithicine brains and Homo sapiens brains
>>>would be the same if subjected to the same set of environemntal effects?

>>How ever did you derive from what I said that conclusion???
>Because you said that heritability may not have explained the
>evolutionary increase in homonid cranial capacity.

If you include "development" as heritable, I guess that would appear to
negate even my caveat about brain size. But it also denies the apparent fact
that human development since Neanderthal times appears to be fixed as well,
with some exceptions I think explained more parsimoniously by diet and
nutrition than evolutionary changes in "development." (We may, however,
generate some discussion about "giants" and "pygmies," or medieval stature
versus modern populations, or first generation immigrants and their
offspring, in relation to head and body size ratios and the possible evidence
for evolutionary trends!?)

Quote:
>>>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?
>Gotchya. I misread you as meaning to include erectus.

No problema!

Cheers,

--Lenny__



Mon, 15 Feb 1999 03:00:00 GMT
 Brain size, IQ

Quote:


>Subject: Re: Brain size, IQ
>Date: 26 Aug 1996 14:35:36 -0600



>>>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.

Quote:
>>I am not familiar with Dawkin's hypothesis, but you would be mistaken about
>>the uncontroversialness of your statement.
>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.

Quote:
>Heritability means, evolutionarily, "not fixed."  That is, genetic or
>allelic variability is responsible for phenotypic variability for a given
>trait.  Once an allele is fixed in a population, heritability is zero,
>because everybody has the same allele for that trait, and phenotypic
>variation in that trait cannot be accounted for genetically.
>>The evolutionary significance of altered developmental ratios for humans,
>>seems to affect the sexes differently. Females appear to experience prolonged
>>developmental growth with respect to males, thus  apparently increasing the
>>time and development of the neural net. A byproduct of this developmental
>>retardation may just be something measurable by the human IQ test. Who knows?

The girls develop faster than the boys, initially, when considered as two
groups.  This is primarily due to the process of masculinization during
childhood from age six through puberty.  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.

Quote:
>I don't follow this.  Sorry. Could you reword this?  

I agree with Bryant, you should reword your paragraph.

Quote:
>Bryant

Wouldn't you like to soar like an Eagle?
In the past, philosophy was based on logic and reasoning rather than observations
recorded using the scientific method.  Realistic Idealism draws its principles from facts
determined through science.  In the past, ostensibly, facts were few and far between.
They were not near enough together to be closely related.  To relate them, one had to
bridge long gaps with logic.  We now know so much that we can travel great distances
in reason without losing touch with factuality.
To many people, a logical subject is right, and to be right is to be logical.  But logic is
a relationship of ideas; ideas that may have no connection with facts.  To many people,
a philosophy bound to facts seems laden down.  With that limitation, a philosopher
is not free to fly with his imagination.  Consequently, a Realistic Idealist needs a
certain humility, for he/she is required to hew to a factual line.  In Realistic Idealism,
one does not soar like an Eagle.  It is more like exploring a railroad track on foot.
Join our exploration.
richard f hall
http://www.***.com/ ~realistic/idealism.html


Mon, 15 Feb 1999 03:00:00 GMT
 Brain size, IQ



|> >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.

--
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
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.



Mon, 15 Feb 1999 03:00:00 GMT
 Brain size, IQ



Quote:

>This is only a bit contriversial in that the cranial capacity is not the
>ultimate gauge of "intelligence".  

Of course not; evolutionary theory predicts that the brain is a collection
of task-specific information processing modules, not a general purpose
computer.  But, for whatever reason, psychometric intelligence ("IQ")
*does* correlate with brain size, to some extent.  It seems to be a
rough, crude gauge, and there are plenty of anecdotal exceptions (but
those don't reduce the statistical significance of the trend).

Quote:
>>>I am not familiar with Dawkin's hypothesis, but you would be mistaken about
>>>the uncontroversialness of your statement.

What I hoped would be uncontroversial is the notion that brain size was
heritable, at least until relatively recently in hominid evolution.  The
evidence for this is the increasing cranial capacity of fossil hominids
as the lineage 'progressed.'

Quote:
>>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.

Nice example. This may be relevant to the issue of the evolution of
intelligence, but does not answer my above question: what's controversial
about cranial capacity *itself* being heritable in ancestral popualtions?

Bryant



Mon, 15 Feb 1999 03:00:00 GMT
 Brain size, IQ

Quote:

> There's been some discussion of IQ on sci.anthropology lately, and I'd
> appreciate any feedback from the interested and informed parties about my
> questions below.  Thanks.

My feeling is that their is little or no point to the discussion of
IQ, because the discussions (at least the ones I have seen) take the
notion of "IQ" for granted as a measure of something called
"intelligence".  I see the same thing happen in many discussions of
"race" where a North American emic taxonomy is assumed to be
biologically and etically correct and relevant to all H. sapiens.

"IQ" represents performance on a particular test, called an "IQ test",
by a particular individual at a particular time and place.  As far as
I know, no one has ever proven that this measure represents
something "real" inside the heads of the people who take the tests.
Indeed, has anyone ever shown that there is, in fact, a "thing"
which can be called "intelligence" residing inside the heads of
humans or any other species?  I don't think so.

Furthermore, the original stated purpose of the "IQ" test as conceived
by Binet was to identify children in schools who needed extra help.
The tests are now used to identify children who presumably
won't benefit from the goodies the "intelligent" children are destined
to receive.  The reason usually given for this is that since we have
limited educational resources, the resources need to be aimed at the
children who can "benefit" the most from them.  This is bogus
reasoning; we should be insisting that all children receive all the
resources they need (educational and otherwise) and we should be
assuming that all children can benefit from the goodies until they
themselves prove otherwise.  I believe that we, as anthropologists,
are in a unique position to argue for this kind of educational policy;
I also believe that we should be arguing for it.

Ron Kephart
University of North Florida



Thu, 18 Feb 1999 03:00:00 GMT
 
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