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alternative hypothesis for brain size



 
 
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  #1  
Old March 27th 04, 03:23 PM
elzinator
external usenet poster
 
Posts: n/a
Default alternative hypothesis for brain size

With all the furor of the recent article in Nature (in which the MHC
mutation/brain size hypothesis is not being well received in the
academic community), this occurred on one of the science usenet groups
I read:

Big Brains and Bipedalism

One of the reasons often quoted for the limit on human brain size, is
the
restriction placed on head size due to childbirth. In bipedal humans,
childbirth poses a serious risk for both mother and child (mortality
rates
increasing for both), because the newborn must now pass out of a
narrow
birth canal between the narrower pelvis hips (which have evolved for
an
upright posture). This is a problem not experienced to the same degree
by
quadrupeds. It is now well established that bipedalism evolved first
followed by large brains. To me this seems something of a paradox
because we
have a trait, bipedalism (with its associated narrower birth canal and
increased mortality) which would seem to place selective pressure on
smaller
heads (and associated brains), not larger. The adaptive value of
larger
brains must now be explained as being very significant in order to
overcome
this reverse trend which would have been expected.

I would now like to suggest an alternate hypothesis, which is, that
larger
brains are a direct result of bipedalism and difficult child birth
rather
than the opposite.

Let me explain.
Because of bipedalism and its associated difficult childbirth,
evolution has
come up with a partial solution for the big head problem, (neoteny
being
one), and also a softer, (less rigid) more plastic or malleable skull
during
childbirth. Humans at birth have not only a hole in the top of the
skull but
also the skull cap is extremely soft with radial unhealed fractures
running
in all directions. (If you have every seen a newborn immediately after
birth, their heads look like squashed prunes). Only bipedal humans
have this
trait, quadrupeds have much more hard and rigid skulls with little
deformation (its not needed), their skulls size (while they still
grow) are
more set at birth.

Could it be that the physiology of brain growth is such that they
simply
grow to their container size? and that the pressure of a growing brain
in a
softer more plastic skull has resulted in a larger brain before the
skull
matures (heals) into a more rigid one. Skulls do not grow to
accommodate a
predetermined brain size, the opposite is true, brains grow to fit a
genetically determined skull size. When you think about it, brains
exactly
fit skulls. This may seem intuitively obvious, but wait, other body
organs
cannot follow this growing strategy, because they are not enclosed
(and
subsequently restrained) in a rigid structure like a boney skull. This
is
why (as any surgeon will attest) organs can and do vary in size
constrained
only by an inherited genetic growth limit. Is it possible that brains
follow
a different growth strategy. The physiology of brain growth may be
different
from other organs, relying more on the pressure of the container size
to
restrict growth rather than having a preset genetic size, (the folds
in the
brain may have something to do with this pressure growth relation).
One
observation seems to confirm this, which is, have you ever heard of a
person
with a large skull but a small brain, the answer is of course no,
brains
always grow to container size. If brain size of an individual is
predetermined by inherited genetics (skull size most certainly is) we
should
expect statistically to see varying sizes of brains to skulls (small
brain,
large skull, would be one) and of course we don't. If this idea is
correct,
large Brains would now seem to be a physiological development
phenomenon
rather than a naturally selected adaptive trait.

The traits usually quoted as the adaptive reasons for big brains,
speech,
mental maps, group hunting, social situation manipulators, heat
radiators,
tool use, dexterity (opposable thumbs) etc. can now be viewed as
exaptations
(which are not the reasons for large brains but a consequence of
them),
which have found utility within the confines of a larger brain. Of
course
once any or all of the above traits become incipient, a positive
feedback
loop would set in reinforcing the value of the larger brain.

So there it is,
1- Bipedalism evolves for some reason,
2- Childbirth with rigid skulls increases mortality rates,
3- Soft, plastic more malleable skulls are naturally selected for,
4- Neotenist brain growth restricted by the pressure of the container
now
pushes on a more malleable skull,
5- Large brains. .... Could it be this simple ....

Gould would have liked this, he favors more random, contingent
processes.

Are there any stats to indicate larger [or smaller] brains in c
sections?
Any correlations with IQ? (I believe there is).
A good Grad thesis would be to remove mouse embryos and place radial
cuts in
skull caps, replace to term and measure brain growth to size.

Anyway, this is all off the top of my hard rigid head."
Beelzibub

The human in us owes fealty to humanity. But the wolf in us acknowledges no master.
  #2  
Old March 27th 04, 06:08 PM
Proton Soup
external usenet poster
 
Posts: n/a
Default alternative hypothesis for brain size

On Sat, 27 Mar 2004 08:23:50 -0600, elzinator
wrote:

With all the furor of the recent article in Nature (in which the MHC
mutation/brain size hypothesis is not being well received in the
academic community), this occurred on one of the science usenet groups
I read:

Big Brains and Bipedalism

One of the reasons often quoted for the limit on human brain size, is
the
restriction placed on head size due to childbirth. In bipedal humans,
childbirth poses a serious risk for both mother and child (mortality
rates
increasing for both), because the newborn must now pass out of a
narrow
birth canal between the narrower pelvis hips (which have evolved for
an
upright posture). This is a problem not experienced to the same degree
by
quadrupeds. It is now well established that bipedalism evolved first
followed by large brains. To me this seems something of a paradox
because we
have a trait, bipedalism (with its associated narrower birth canal and
increased mortality) which would seem to place selective pressure on
smaller
heads (and associated brains), not larger. The adaptive value of
larger
brains must now be explained as being very significant in order to
overcome
this reverse trend which would have been expected.

I would now like to suggest an alternate hypothesis, which is, that
larger
brains are a direct result of bipedalism and difficult child birth
rather
than the opposite.

Let me explain.
Because of bipedalism and its associated difficult childbirth,
evolution has
come up with a partial solution for the big head problem, (neoteny
being
one), and also a softer, (less rigid) more plastic or malleable skull
during
childbirth. Humans at birth have not only a hole in the top of the
skull but
also the skull cap is extremely soft with radial unhealed fractures
running
in all directions. (If you have every seen a newborn immediately after
birth, their heads look like squashed prunes). Only bipedal humans
have this
trait, quadrupeds have much more hard and rigid skulls with little
deformation (its not needed), their skulls size (while they still
grow) are
more set at birth.

Could it be that the physiology of brain growth is such that they
simply
grow to their container size? and that the pressure of a growing brain
in a
softer more plastic skull has resulted in a larger brain before the
skull
matures (heals) into a more rigid one. Skulls do not grow to
accommodate a
predetermined brain size, the opposite is true, brains grow to fit a
genetically determined skull size. When you think about it, brains
exactly
fit skulls. This may seem intuitively obvious, but wait, other body
organs
cannot follow this growing strategy, because they are not enclosed
(and
subsequently restrained) in a rigid structure like a boney skull. This
is
why (as any surgeon will attest) organs can and do vary in size
constrained
only by an inherited genetic growth limit. Is it possible that brains
follow
a different growth strategy. The physiology of brain growth may be
different
from other organs, relying more on the pressure of the container size
to
restrict growth rather than having a preset genetic size, (the folds
in the
brain may have something to do with this pressure growth relation).
One
observation seems to confirm this, which is, have you ever heard of a
person
with a large skull but a small brain, the answer is of course no,
brains
always grow to container size. If brain size of an individual is
predetermined by inherited genetics (skull size most certainly is) we
should
expect statistically to see varying sizes of brains to skulls (small
brain,
large skull, would be one) and of course we don't. If this idea is
correct,
large Brains would now seem to be a physiological development
phenomenon
rather than a naturally selected adaptive trait.

The traits usually quoted as the adaptive reasons for big brains,
speech,
mental maps, group hunting, social situation manipulators, heat
radiators,
tool use, dexterity (opposable thumbs) etc. can now be viewed as
exaptations
(which are not the reasons for large brains but a consequence of
them),
which have found utility within the confines of a larger brain. Of
course
once any or all of the above traits become incipient, a positive
feedback
loop would set in reinforcing the value of the larger brain.

So there it is,
1- Bipedalism evolves for some reason,
2- Childbirth with rigid skulls increases mortality rates,
3- Soft, plastic more malleable skulls are naturally selected for,
4- Neotenist brain growth restricted by the pressure of the container
now
pushes on a more malleable skull,
5- Large brains. .... Could it be this simple ....

Gould would have liked this, he favors more random, contingent
processes.

Are there any stats to indicate larger [or smaller] brains in c
sections?


Cool, I was already thinking about caesarians before I read this. But
it seems like it might take a couple of generations to show up
significantly. Guess it would depend somewhat on whether the
selection process just leads to hard-headed kids, or if perhaps the
birthing process itself is important, that is, priming the skull to be
more malleable somehow.

Any correlations with IQ? (I believe there is).
A good Grad thesis would be to remove mouse embryos and place radial
cuts in
skull caps, replace to term and measure brain growth to size.

Anyway, this is all off the top of my hard rigid head."
Beelzibub

The human in us owes fealty to humanity. But the wolf in us acknowledges no master.


Proton Soup

  #3  
Old March 27th 04, 06:08 PM
Proton Soup
external usenet poster
 
Posts: n/a
Default alternative hypothesis for brain size

On Sat, 27 Mar 2004 08:23:50 -0600, elzinator
wrote:

With all the furor of the recent article in Nature (in which the MHC
mutation/brain size hypothesis is not being well received in the
academic community), this occurred on one of the science usenet groups
I read:

Big Brains and Bipedalism

One of the reasons often quoted for the limit on human brain size, is
the
restriction placed on head size due to childbirth. In bipedal humans,
childbirth poses a serious risk for both mother and child (mortality
rates
increasing for both), because the newborn must now pass out of a
narrow
birth canal between the narrower pelvis hips (which have evolved for
an
upright posture). This is a problem not experienced to the same degree
by
quadrupeds. It is now well established that bipedalism evolved first
followed by large brains. To me this seems something of a paradox
because we
have a trait, bipedalism (with its associated narrower birth canal and
increased mortality) which would seem to place selective pressure on
smaller
heads (and associated brains), not larger. The adaptive value of
larger
brains must now be explained as being very significant in order to
overcome
this reverse trend which would have been expected.

I would now like to suggest an alternate hypothesis, which is, that
larger
brains are a direct result of bipedalism and difficult child birth
rather
than the opposite.

Let me explain.
Because of bipedalism and its associated difficult childbirth,
evolution has
come up with a partial solution for the big head problem, (neoteny
being
one), and also a softer, (less rigid) more plastic or malleable skull
during
childbirth. Humans at birth have not only a hole in the top of the
skull but
also the skull cap is extremely soft with radial unhealed fractures
running
in all directions. (If you have every seen a newborn immediately after
birth, their heads look like squashed prunes). Only bipedal humans
have this
trait, quadrupeds have much more hard and rigid skulls with little
deformation (its not needed), their skulls size (while they still
grow) are
more set at birth.

Could it be that the physiology of brain growth is such that they
simply
grow to their container size? and that the pressure of a growing brain
in a
softer more plastic skull has resulted in a larger brain before the
skull
matures (heals) into a more rigid one. Skulls do not grow to
accommodate a
predetermined brain size, the opposite is true, brains grow to fit a
genetically determined skull size. When you think about it, brains
exactly
fit skulls. This may seem intuitively obvious, but wait, other body
organs
cannot follow this growing strategy, because they are not enclosed
(and
subsequently restrained) in a rigid structure like a boney skull. This
is
why (as any surgeon will attest) organs can and do vary in size
constrained
only by an inherited genetic growth limit. Is it possible that brains
follow
a different growth strategy. The physiology of brain growth may be
different
from other organs, relying more on the pressure of the container size
to
restrict growth rather than having a preset genetic size, (the folds
in the
brain may have something to do with this pressure growth relation).
One
observation seems to confirm this, which is, have you ever heard of a
person
with a large skull but a small brain, the answer is of course no,
brains
always grow to container size. If brain size of an individual is
predetermined by inherited genetics (skull size most certainly is) we
should
expect statistically to see varying sizes of brains to skulls (small
brain,
large skull, would be one) and of course we don't. If this idea is
correct,
large Brains would now seem to be a physiological development
phenomenon
rather than a naturally selected adaptive trait.

The traits usually quoted as the adaptive reasons for big brains,
speech,
mental maps, group hunting, social situation manipulators, heat
radiators,
tool use, dexterity (opposable thumbs) etc. can now be viewed as
exaptations
(which are not the reasons for large brains but a consequence of
them),
which have found utility within the confines of a larger brain. Of
course
once any or all of the above traits become incipient, a positive
feedback
loop would set in reinforcing the value of the larger brain.

So there it is,
1- Bipedalism evolves for some reason,
2- Childbirth with rigid skulls increases mortality rates,
3- Soft, plastic more malleable skulls are naturally selected for,
4- Neotenist brain growth restricted by the pressure of the container
now
pushes on a more malleable skull,
5- Large brains. .... Could it be this simple ....

Gould would have liked this, he favors more random, contingent
processes.

Are there any stats to indicate larger [or smaller] brains in c
sections?


Cool, I was already thinking about caesarians before I read this. But
it seems like it might take a couple of generations to show up
significantly. Guess it would depend somewhat on whether the
selection process just leads to hard-headed kids, or if perhaps the
birthing process itself is important, that is, priming the skull to be
more malleable somehow.

Any correlations with IQ? (I believe there is).
A good Grad thesis would be to remove mouse embryos and place radial
cuts in
skull caps, replace to term and measure brain growth to size.

Anyway, this is all off the top of my hard rigid head."
Beelzibub

The human in us owes fealty to humanity. But the wolf in us acknowledges no master.


Proton Soup

  #4  
Old March 27th 04, 09:39 PM
Lee Michaels
external usenet poster
 
Posts: n/a
Default alternative hypothesis for brain size


"elzinator" wrote in message
...
With all the furor of the recent article in Nature (in which the MHC
mutation/brain size hypothesis is not being well received in the
academic community), this occurred on one of the science usenet groups
I read:

Big Brains and Bipedalism

One of the reasons often quoted for the limit on human brain size, is
the
restriction placed on head size due to childbirth. In bipedal humans,
childbirth poses a serious risk for both mother and child (mortality
rates
increasing for both), because the newborn must now pass out of a
narrow
birth canal between the narrower pelvis hips (which have evolved for
an
upright posture). This is a problem not experienced to the same degree
by
quadrupeds. It is now well established that bipedalism evolved first
followed by large brains. To me this seems something of a paradox
because we
have a trait, bipedalism (with its associated narrower birth canal and
increased mortality) which would seem to place selective pressure on
smaller
heads (and associated brains), not larger. The adaptive value of
larger
brains must now be explained as being very significant in order to
overcome
this reverse trend which would have been expected.

I would now like to suggest an alternate hypothesis, which is, that
larger
brains are a direct result of bipedalism and difficult child birth
rather
than the opposite.

Let me explain.
Because of bipedalism and its associated difficult childbirth,
evolution has
come up with a partial solution for the big head problem, (neoteny
being
one), and also a softer, (less rigid) more plastic or malleable skull
during
childbirth. Humans at birth have not only a hole in the top of the
skull but
also the skull cap is extremely soft with radial unhealed fractures
running
in all directions. (If you have every seen a newborn immediately after
birth, their heads look like squashed prunes). Only bipedal humans
have this
trait, quadrupeds have much more hard and rigid skulls with little
deformation (its not needed), their skulls size (while they still
grow) are
more set at birth.

Could it be that the physiology of brain growth is such that they
simply
grow to their container size? and that the pressure of a growing brain
in a
softer more plastic skull has resulted in a larger brain before the
skull
matures (heals) into a more rigid one. Skulls do not grow to
accommodate a
predetermined brain size, the opposite is true, brains grow to fit a
genetically determined skull size. When you think about it, brains
exactly
fit skulls. This may seem intuitively obvious, but wait, other body
organs
cannot follow this growing strategy, because they are not enclosed
(and
subsequently restrained) in a rigid structure like a boney skull. This
is
why (as any surgeon will attest) organs can and do vary in size
constrained
only by an inherited genetic growth limit. Is it possible that brains
follow
a different growth strategy. The physiology of brain growth may be
different
from other organs, relying more on the pressure of the container size
to
restrict growth rather than having a preset genetic size, (the folds
in the
brain may have something to do with this pressure growth relation).
One
observation seems to confirm this, which is, have you ever heard of a
person
with a large skull but a small brain, the answer is of course no,
brains
always grow to container size. If brain size of an individual is
predetermined by inherited genetics (skull size most certainly is) we
should
expect statistically to see varying sizes of brains to skulls (small
brain,
large skull, would be one) and of course we don't. If this idea is
correct,
large Brains would now seem to be a physiological development
phenomenon
rather than a naturally selected adaptive trait.

The traits usually quoted as the adaptive reasons for big brains,
speech,
mental maps, group hunting, social situation manipulators, heat
radiators,
tool use, dexterity (opposable thumbs) etc. can now be viewed as
exaptations
(which are not the reasons for large brains but a consequence of
them),
which have found utility within the confines of a larger brain. Of
course
once any or all of the above traits become incipient, a positive
feedback
loop would set in reinforcing the value of the larger brain.

So there it is,
1- Bipedalism evolves for some reason,
2- Childbirth with rigid skulls increases mortality rates,
3- Soft, plastic more malleable skulls are naturally selected for,
4- Neotenist brain growth restricted by the pressure of the container
now
pushes on a more malleable skull,
5- Large brains. .... Could it be this simple ....

Gould would have liked this, he favors more random, contingent
processes.

Are there any stats to indicate larger [or smaller] brains in c
sections?
Any correlations with IQ? (I believe there is).
A good Grad thesis would be to remove mouse embryos and place radial
cuts in
skull caps, replace to term and measure brain growth to size.

Anyway, this is all off the top of my hard rigid head."


Good stuff Elzi.

Out of the context of the above argument, what hapens when the skull does
not expand as fully as it could. But still is at least normal if not bigger
size?

Let me explain. I knew a couple people who skull plates did not become rigid
in the normal manner. They were told by docs that the plates fused too early
while growing. But they have either normal or above normal sized skulls.
Both people are very smart. Each has a ridge down the top of the skull.

It would seem, out of the context of the above argument, that if these
skulls have been allowed to grow larger, their brains would have been
bigger. And as such, these individuals may have been even more intelligent.

Does this sound reasonable?



  #5  
Old March 27th 04, 09:39 PM
Lee Michaels
external usenet poster
 
Posts: n/a
Default alternative hypothesis for brain size


"elzinator" wrote in message
...
With all the furor of the recent article in Nature (in which the MHC
mutation/brain size hypothesis is not being well received in the
academic community), this occurred on one of the science usenet groups
I read:

Big Brains and Bipedalism

One of the reasons often quoted for the limit on human brain size, is
the
restriction placed on head size due to childbirth. In bipedal humans,
childbirth poses a serious risk for both mother and child (mortality
rates
increasing for both), because the newborn must now pass out of a
narrow
birth canal between the narrower pelvis hips (which have evolved for
an
upright posture). This is a problem not experienced to the same degree
by
quadrupeds. It is now well established that bipedalism evolved first
followed by large brains. To me this seems something of a paradox
because we
have a trait, bipedalism (with its associated narrower birth canal and
increased mortality) which would seem to place selective pressure on
smaller
heads (and associated brains), not larger. The adaptive value of
larger
brains must now be explained as being very significant in order to
overcome
this reverse trend which would have been expected.

I would now like to suggest an alternate hypothesis, which is, that
larger
brains are a direct result of bipedalism and difficult child birth
rather
than the opposite.

Let me explain.
Because of bipedalism and its associated difficult childbirth,
evolution has
come up with a partial solution for the big head problem, (neoteny
being
one), and also a softer, (less rigid) more plastic or malleable skull
during
childbirth. Humans at birth have not only a hole in the top of the
skull but
also the skull cap is extremely soft with radial unhealed fractures
running
in all directions. (If you have every seen a newborn immediately after
birth, their heads look like squashed prunes). Only bipedal humans
have this
trait, quadrupeds have much more hard and rigid skulls with little
deformation (its not needed), their skulls size (while they still
grow) are
more set at birth.

Could it be that the physiology of brain growth is such that they
simply
grow to their container size? and that the pressure of a growing brain
in a
softer more plastic skull has resulted in a larger brain before the
skull
matures (heals) into a more rigid one. Skulls do not grow to
accommodate a
predetermined brain size, the opposite is true, brains grow to fit a
genetically determined skull size. When you think about it, brains
exactly
fit skulls. This may seem intuitively obvious, but wait, other body
organs
cannot follow this growing strategy, because they are not enclosed
(and
subsequently restrained) in a rigid structure like a boney skull. This
is
why (as any surgeon will attest) organs can and do vary in size
constrained
only by an inherited genetic growth limit. Is it possible that brains
follow
a different growth strategy. The physiology of brain growth may be
different
from other organs, relying more on the pressure of the container size
to
restrict growth rather than having a preset genetic size, (the folds
in the
brain may have something to do with this pressure growth relation).
One
observation seems to confirm this, which is, have you ever heard of a
person
with a large skull but a small brain, the answer is of course no,
brains
always grow to container size. If brain size of an individual is
predetermined by inherited genetics (skull size most certainly is) we
should
expect statistically to see varying sizes of brains to skulls (small
brain,
large skull, would be one) and of course we don't. If this idea is
correct,
large Brains would now seem to be a physiological development
phenomenon
rather than a naturally selected adaptive trait.

The traits usually quoted as the adaptive reasons for big brains,
speech,
mental maps, group hunting, social situation manipulators, heat
radiators,
tool use, dexterity (opposable thumbs) etc. can now be viewed as
exaptations
(which are not the reasons for large brains but a consequence of
them),
which have found utility within the confines of a larger brain. Of
course
once any or all of the above traits become incipient, a positive
feedback
loop would set in reinforcing the value of the larger brain.

So there it is,
1- Bipedalism evolves for some reason,
2- Childbirth with rigid skulls increases mortality rates,
3- Soft, plastic more malleable skulls are naturally selected for,
4- Neotenist brain growth restricted by the pressure of the container
now
pushes on a more malleable skull,
5- Large brains. .... Could it be this simple ....

Gould would have liked this, he favors more random, contingent
processes.

Are there any stats to indicate larger [or smaller] brains in c
sections?
Any correlations with IQ? (I believe there is).
A good Grad thesis would be to remove mouse embryos and place radial
cuts in
skull caps, replace to term and measure brain growth to size.

Anyway, this is all off the top of my hard rigid head."


Good stuff Elzi.

Out of the context of the above argument, what hapens when the skull does
not expand as fully as it could. But still is at least normal if not bigger
size?

Let me explain. I knew a couple people who skull plates did not become rigid
in the normal manner. They were told by docs that the plates fused too early
while growing. But they have either normal or above normal sized skulls.
Both people are very smart. Each has a ridge down the top of the skull.

It would seem, out of the context of the above argument, that if these
skulls have been allowed to grow larger, their brains would have been
bigger. And as such, these individuals may have been even more intelligent.

Does this sound reasonable?



  #6  
Old March 27th 04, 09:52 PM
AlphaOmega2004
external usenet poster
 
Posts: n/a
Default alternative hypothesis for brain size


"elzinator" wrote in message
...
With all the furor of the recent article in Nature (in which the MHC
mutation/brain size hypothesis is not being well received in the
academic community), this occurred on one of the science usenet groups
I read:

Big Brains and Bipedalism

One of the reasons often quoted for the limit on human brain size, is
the
restriction placed on head size due to childbirth. In bipedal humans,
childbirth poses a serious risk for both mother and child (mortality
rates
increasing for both), because the newborn must now pass out of a
narrow
birth canal between the narrower pelvis hips (which have evolved for
an
upright posture). This is a problem not experienced to the same degree
by
quadrupeds. It is now well established that bipedalism evolved first
followed by large brains. To me this seems something of a paradox
because we
have a trait, bipedalism (with its associated narrower birth canal and
increased mortality) which would seem to place selective pressure on
smaller
heads (and associated brains), not larger. The adaptive value of
larger
brains must now be explained as being very significant in order to
overcome
this reverse trend which would have been expected.

I would now like to suggest an alternate hypothesis, which is, that
larger
brains are a direct result of bipedalism and difficult child birth
rather
than the opposite.

Let me explain.
Because of bipedalism and its associated difficult childbirth,
evolution has
come up with a partial solution for the big head problem, (neoteny
being
one), and also a softer, (less rigid) more plastic or malleable skull
during
childbirth. Humans at birth have not only a hole in the top of the
skull but
also the skull cap is extremely soft with radial unhealed fractures
running
in all directions. (If you have every seen a newborn immediately after
birth, their heads look like squashed prunes). Only bipedal humans
have this
trait, quadrupeds have much more hard and rigid skulls with little
deformation (its not needed), their skulls size (while they still
grow) are
more set at birth.

Could it be that the physiology of brain growth is such that they
simply
grow to their container size? and that the pressure of a growing brain
in a
softer more plastic skull has resulted in a larger brain before the
skull
matures (heals) into a more rigid one. Skulls do not grow to
accommodate a
predetermined brain size, the opposite is true, brains grow to fit a
genetically determined skull size. When you think about it, brains
exactly
fit skulls. This may seem intuitively obvious, but wait, other body
organs
cannot follow this growing strategy, because they are not enclosed
(and
subsequently restrained) in a rigid structure like a boney skull. This
is
why (as any surgeon will attest) organs can and do vary in size
constrained
only by an inherited genetic growth limit. Is it possible that brains
follow
a different growth strategy. The physiology of brain growth may be
different
from other organs, relying more on the pressure of the container size
to
restrict growth rather than having a preset genetic size, (the folds
in the
brain may have something to do with this pressure growth relation).
One
observation seems to confirm this, which is, have you ever heard of a
person
with a large skull but a small brain, the answer is of course no,
brains
always grow to container size. If brain size of an individual is
predetermined by inherited genetics (skull size most certainly is) we
should
expect statistically to see varying sizes of brains to skulls (small
brain,
large skull, would be one) and of course we don't. If this idea is
correct,
large Brains would now seem to be a physiological development
phenomenon
rather than a naturally selected adaptive trait.

The traits usually quoted as the adaptive reasons for big brains,
speech,
mental maps, group hunting, social situation manipulators, heat
radiators,
tool use, dexterity (opposable thumbs) etc. can now be viewed as
exaptations
(which are not the reasons for large brains but a consequence of
them),
which have found utility within the confines of a larger brain. Of
course
once any or all of the above traits become incipient, a positive
feedback
loop would set in reinforcing the value of the larger brain.

So there it is,
1- Bipedalism evolves for some reason,
2- Childbirth with rigid skulls increases mortality rates,
3- Soft, plastic more malleable skulls are naturally selected for,
4- Neotenist brain growth restricted by the pressure of the container
now
pushes on a more malleable skull,
5- Large brains. .... Could it be this simple ....

Gould would have liked this, he favors more random, contingent
processes.

Are there any stats to indicate larger [or smaller] brains in c
sections?
Any correlations with IQ? (I believe there is).


There is more of a correlation )of IQ) with the relative number of glial
cells (not Swanns mind you - astrocytes and oligodendrocytes) to neurons
than size/volume per se. We know the various ATP-mediated communications
mechanisms among the glia and betwixt the glia and neurons, and that that
evidence points to/supports several functional cognitive enhancments in
which glia are involved over and above their normal scenarios (e.g.,
Einsteinn's brain).

AS for what came first - the history of evolution is one of environmental
contingencies contribnuting to parallel development of new functional
capabilities *and* the CNS mechanisms to support such. A little bit of this
then a little bit of that, then a little bit more of this, then...... There
are exceptions (the whole PE scenario of which Gould is the high priest of
proseyltizment (new word)), but the soft-skull scenario did not contribute
*all at once* to the cerebral cortex we now enjoy. That there are several
functional areas fo such, all interacting with different sets of
environmental contingencies should be a clue in that direction.





  #7  
Old March 27th 04, 09:52 PM
AlphaOmega2004
external usenet poster
 
Posts: n/a
Default alternative hypothesis for brain size


"elzinator" wrote in message
...
With all the furor of the recent article in Nature (in which the MHC
mutation/brain size hypothesis is not being well received in the
academic community), this occurred on one of the science usenet groups
I read:

Big Brains and Bipedalism

One of the reasons often quoted for the limit on human brain size, is
the
restriction placed on head size due to childbirth. In bipedal humans,
childbirth poses a serious risk for both mother and child (mortality
rates
increasing for both), because the newborn must now pass out of a
narrow
birth canal between the narrower pelvis hips (which have evolved for
an
upright posture). This is a problem not experienced to the same degree
by
quadrupeds. It is now well established that bipedalism evolved first
followed by large brains. To me this seems something of a paradox
because we
have a trait, bipedalism (with its associated narrower birth canal and
increased mortality) which would seem to place selective pressure on
smaller
heads (and associated brains), not larger. The adaptive value of
larger
brains must now be explained as being very significant in order to
overcome
this reverse trend which would have been expected.

I would now like to suggest an alternate hypothesis, which is, that
larger
brains are a direct result of bipedalism and difficult child birth
rather
than the opposite.

Let me explain.
Because of bipedalism and its associated difficult childbirth,
evolution has
come up with a partial solution for the big head problem, (neoteny
being
one), and also a softer, (less rigid) more plastic or malleable skull
during
childbirth. Humans at birth have not only a hole in the top of the
skull but
also the skull cap is extremely soft with radial unhealed fractures
running
in all directions. (If you have every seen a newborn immediately after
birth, their heads look like squashed prunes). Only bipedal humans
have this
trait, quadrupeds have much more hard and rigid skulls with little
deformation (its not needed), their skulls size (while they still
grow) are
more set at birth.

Could it be that the physiology of brain growth is such that they
simply
grow to their container size? and that the pressure of a growing brain
in a
softer more plastic skull has resulted in a larger brain before the
skull
matures (heals) into a more rigid one. Skulls do not grow to
accommodate a
predetermined brain size, the opposite is true, brains grow to fit a
genetically determined skull size. When you think about it, brains
exactly
fit skulls. This may seem intuitively obvious, but wait, other body
organs
cannot follow this growing strategy, because they are not enclosed
(and
subsequently restrained) in a rigid structure like a boney skull. This
is
why (as any surgeon will attest) organs can and do vary in size
constrained
only by an inherited genetic growth limit. Is it possible that brains
follow
a different growth strategy. The physiology of brain growth may be
different
from other organs, relying more on the pressure of the container size
to
restrict growth rather than having a preset genetic size, (the folds
in the
brain may have something to do with this pressure growth relation).
One
observation seems to confirm this, which is, have you ever heard of a
person
with a large skull but a small brain, the answer is of course no,
brains
always grow to container size. If brain size of an individual is
predetermined by inherited genetics (skull size most certainly is) we
should
expect statistically to see varying sizes of brains to skulls (small
brain,
large skull, would be one) and of course we don't. If this idea is
correct,
large Brains would now seem to be a physiological development
phenomenon
rather than a naturally selected adaptive trait.

The traits usually quoted as the adaptive reasons for big brains,
speech,
mental maps, group hunting, social situation manipulators, heat
radiators,
tool use, dexterity (opposable thumbs) etc. can now be viewed as
exaptations
(which are not the reasons for large brains but a consequence of
them),
which have found utility within the confines of a larger brain. Of
course
once any or all of the above traits become incipient, a positive
feedback
loop would set in reinforcing the value of the larger brain.

So there it is,
1- Bipedalism evolves for some reason,
2- Childbirth with rigid skulls increases mortality rates,
3- Soft, plastic more malleable skulls are naturally selected for,
4- Neotenist brain growth restricted by the pressure of the container
now
pushes on a more malleable skull,
5- Large brains. .... Could it be this simple ....

Gould would have liked this, he favors more random, contingent
processes.

Are there any stats to indicate larger [or smaller] brains in c
sections?
Any correlations with IQ? (I believe there is).


There is more of a correlation )of IQ) with the relative number of glial
cells (not Swanns mind you - astrocytes and oligodendrocytes) to neurons
than size/volume per se. We know the various ATP-mediated communications
mechanisms among the glia and betwixt the glia and neurons, and that that
evidence points to/supports several functional cognitive enhancments in
which glia are involved over and above their normal scenarios (e.g.,
Einsteinn's brain).

AS for what came first - the history of evolution is one of environmental
contingencies contribnuting to parallel development of new functional
capabilities *and* the CNS mechanisms to support such. A little bit of this
then a little bit of that, then a little bit more of this, then...... There
are exceptions (the whole PE scenario of which Gould is the high priest of
proseyltizment (new word)), but the soft-skull scenario did not contribute
*all at once* to the cerebral cortex we now enjoy. That there are several
functional areas fo such, all interacting with different sets of
environmental contingencies should be a clue in that direction.





  #8  
Old March 27th 04, 09:55 PM
AlphaOmega2004
external usenet poster
 
Posts: n/a
Default alternative hypothesis for brain size


"Lee Michaels" wrote in message
news:[email protected]_s01...

"elzinator" wrote in message
...
With all the furor of the recent article in Nature (in which the MHC
mutation/brain size hypothesis is not being well received in the
academic community), this occurred on one of the science usenet groups
I read:

Big Brains and Bipedalism

One of the reasons often quoted for the limit on human brain size, is
the
restriction placed on head size due to childbirth. In bipedal humans,
childbirth poses a serious risk for both mother and child (mortality
rates
increasing for both), because the newborn must now pass out of a
narrow
birth canal between the narrower pelvis hips (which have evolved for
an
upright posture). This is a problem not experienced to the same degree
by
quadrupeds. It is now well established that bipedalism evolved first
followed by large brains. To me this seems something of a paradox
because we
have a trait, bipedalism (with its associated narrower birth canal and
increased mortality) which would seem to place selective pressure on
smaller
heads (and associated brains), not larger. The adaptive value of
larger
brains must now be explained as being very significant in order to
overcome
this reverse trend which would have been expected.

I would now like to suggest an alternate hypothesis, which is, that
larger
brains are a direct result of bipedalism and difficult child birth
rather
than the opposite.

Let me explain.
Because of bipedalism and its associated difficult childbirth,
evolution has
come up with a partial solution for the big head problem, (neoteny
being
one), and also a softer, (less rigid) more plastic or malleable skull
during
childbirth. Humans at birth have not only a hole in the top of the
skull but
also the skull cap is extremely soft with radial unhealed fractures
running
in all directions. (If you have every seen a newborn immediately after
birth, their heads look like squashed prunes). Only bipedal humans
have this
trait, quadrupeds have much more hard and rigid skulls with little
deformation (its not needed), their skulls size (while they still
grow) are
more set at birth.

Could it be that the physiology of brain growth is such that they
simply
grow to their container size? and that the pressure of a growing brain
in a
softer more plastic skull has resulted in a larger brain before the
skull
matures (heals) into a more rigid one. Skulls do not grow to
accommodate a
predetermined brain size, the opposite is true, brains grow to fit a
genetically determined skull size. When you think about it, brains
exactly
fit skulls. This may seem intuitively obvious, but wait, other body
organs
cannot follow this growing strategy, because they are not enclosed
(and
subsequently restrained) in a rigid structure like a boney skull. This
is
why (as any surgeon will attest) organs can and do vary in size
constrained
only by an inherited genetic growth limit. Is it possible that brains
follow
a different growth strategy. The physiology of brain growth may be
different
from other organs, relying more on the pressure of the container size
to
restrict growth rather than having a preset genetic size, (the folds
in the
brain may have something to do with this pressure growth relation).
One
observation seems to confirm this, which is, have you ever heard of a
person
with a large skull but a small brain, the answer is of course no,
brains
always grow to container size. If brain size of an individual is
predetermined by inherited genetics (skull size most certainly is) we
should
expect statistically to see varying sizes of brains to skulls (small
brain,
large skull, would be one) and of course we don't. If this idea is
correct,
large Brains would now seem to be a physiological development
phenomenon
rather than a naturally selected adaptive trait.

The traits usually quoted as the adaptive reasons for big brains,
speech,
mental maps, group hunting, social situation manipulators, heat
radiators,
tool use, dexterity (opposable thumbs) etc. can now be viewed as
exaptations
(which are not the reasons for large brains but a consequence of
them),
which have found utility within the confines of a larger brain. Of
course
once any or all of the above traits become incipient, a positive
feedback
loop would set in reinforcing the value of the larger brain.

So there it is,
1- Bipedalism evolves for some reason,
2- Childbirth with rigid skulls increases mortality rates,
3- Soft, plastic more malleable skulls are naturally selected for,
4- Neotenist brain growth restricted by the pressure of the container
now
pushes on a more malleable skull,
5- Large brains. .... Could it be this simple ....

Gould would have liked this, he favors more random, contingent
processes.

Are there any stats to indicate larger [or smaller] brains in c
sections?
Any correlations with IQ? (I believe there is).
A good Grad thesis would be to remove mouse embryos and place radial
cuts in
skull caps, replace to term and measure brain growth to size.

Anyway, this is all off the top of my hard rigid head."


Good stuff Elzi.

Out of the context of the above argument, what hapens when the skull does
not expand as fully as it could. But still is at least normal if not

bigger
size?

Let me explain. I knew a couple people who skull plates did not become

rigid
in the normal manner. They were told by docs that the plates fused too

early
while growing. But they have either normal or above normal sized skulls.
Both people are very smart. Each has a ridge down the top of the skull.

It would seem, out of the context of the above argument, that if these
skulls have been allowed to grow larger, their brains would have been
bigger. And as such, these individuals may have been even more

intelligent.

Does this sound reasonable?


Yes and no. That things seem is not that they are.

Look up phylogeny and ontogeny and then recapitulation. Combine all in a
blender and tell us what you get.








  #9  
Old March 27th 04, 09:55 PM
AlphaOmega2004
external usenet poster
 
Posts: n/a
Default alternative hypothesis for brain size


"Lee Michaels" wrote in message
news:[email protected]_s01...

"elzinator" wrote in message
...
With all the furor of the recent article in Nature (in which the MHC
mutation/brain size hypothesis is not being well received in the
academic community), this occurred on one of the science usenet groups
I read:

Big Brains and Bipedalism

One of the reasons often quoted for the limit on human brain size, is
the
restriction placed on head size due to childbirth. In bipedal humans,
childbirth poses a serious risk for both mother and child (mortality
rates
increasing for both), because the newborn must now pass out of a
narrow
birth canal between the narrower pelvis hips (which have evolved for
an
upright posture). This is a problem not experienced to the same degree
by
quadrupeds. It is now well established that bipedalism evolved first
followed by large brains. To me this seems something of a paradox
because we
have a trait, bipedalism (with its associated narrower birth canal and
increased mortality) which would seem to place selective pressure on
smaller
heads (and associated brains), not larger. The adaptive value of
larger
brains must now be explained as being very significant in order to
overcome
this reverse trend which would have been expected.

I would now like to suggest an alternate hypothesis, which is, that
larger
brains are a direct result of bipedalism and difficult child birth
rather
than the opposite.

Let me explain.
Because of bipedalism and its associated difficult childbirth,
evolution has
come up with a partial solution for the big head problem, (neoteny
being
one), and also a softer, (less rigid) more plastic or malleable skull
during
childbirth. Humans at birth have not only a hole in the top of the
skull but
also the skull cap is extremely soft with radial unhealed fractures
running
in all directions. (If you have every seen a newborn immediately after
birth, their heads look like squashed prunes). Only bipedal humans
have this
trait, quadrupeds have much more hard and rigid skulls with little
deformation (its not needed), their skulls size (while they still
grow) are
more set at birth.

Could it be that the physiology of brain growth is such that they
simply
grow to their container size? and that the pressure of a growing brain
in a
softer more plastic skull has resulted in a larger brain before the
skull
matures (heals) into a more rigid one. Skulls do not grow to
accommodate a
predetermined brain size, the opposite is true, brains grow to fit a
genetically determined skull size. When you think about it, brains
exactly
fit skulls. This may seem intuitively obvious, but wait, other body
organs
cannot follow this growing strategy, because they are not enclosed
(and
subsequently restrained) in a rigid structure like a boney skull. This
is
why (as any surgeon will attest) organs can and do vary in size
constrained
only by an inherited genetic growth limit. Is it possible that brains
follow
a different growth strategy. The physiology of brain growth may be
different
from other organs, relying more on the pressure of the container size
to
restrict growth rather than having a preset genetic size, (the folds
in the
brain may have something to do with this pressure growth relation).
One
observation seems to confirm this, which is, have you ever heard of a
person
with a large skull but a small brain, the answer is of course no,
brains
always grow to container size. If brain size of an individual is
predetermined by inherited genetics (skull size most certainly is) we
should
expect statistically to see varying sizes of brains to skulls (small
brain,
large skull, would be one) and of course we don't. If this idea is
correct,
large Brains would now seem to be a physiological development
phenomenon
rather than a naturally selected adaptive trait.

The traits usually quoted as the adaptive reasons for big brains,
speech,
mental maps, group hunting, social situation manipulators, heat
radiators,
tool use, dexterity (opposable thumbs) etc. can now be viewed as
exaptations
(which are not the reasons for large brains but a consequence of
them),
which have found utility within the confines of a larger brain. Of
course
once any or all of the above traits become incipient, a positive
feedback
loop would set in reinforcing the value of the larger brain.

So there it is,
1- Bipedalism evolves for some reason,
2- Childbirth with rigid skulls increases mortality rates,
3- Soft, plastic more malleable skulls are naturally selected for,
4- Neotenist brain growth restricted by the pressure of the container
now
pushes on a more malleable skull,
5- Large brains. .... Could it be this simple ....

Gould would have liked this, he favors more random, contingent
processes.

Are there any stats to indicate larger [or smaller] brains in c
sections?
Any correlations with IQ? (I believe there is).
A good Grad thesis would be to remove mouse embryos and place radial
cuts in
skull caps, replace to term and measure brain growth to size.

Anyway, this is all off the top of my hard rigid head."


Good stuff Elzi.

Out of the context of the above argument, what hapens when the skull does
not expand as fully as it could. But still is at least normal if not

bigger
size?

Let me explain. I knew a couple people who skull plates did not become

rigid
in the normal manner. They were told by docs that the plates fused too

early
while growing. But they have either normal or above normal sized skulls.
Both people are very smart. Each has a ridge down the top of the skull.

It would seem, out of the context of the above argument, that if these
skulls have been allowed to grow larger, their brains would have been
bigger. And as such, these individuals may have been even more

intelligent.

Does this sound reasonable?


Yes and no. That things seem is not that they are.

Look up phylogeny and ontogeny and then recapitulation. Combine all in a
blender and tell us what you get.








  #10  
Old March 27th 04, 10:37 PM
Kevin J
external usenet poster
 
Posts: n/a
Default alternative hypothesis for brain size

On Sat, 27 Mar 2004 20:52:56 GMT, "AlphaOmega2004"
wrote:


There is more of a correlation )of IQ) with the relative number of glial
cells (not Swanns mind you - astrocytes and oligodendrocytes) to neurons
than size/volume per se.


Do you have a source for this? I wouldn't mind reading the study.

We know the various ATP-mediated communications
mechanisms among the glia and betwixt the glia and neurons,


What do you mean by ATP-mediated communications? I know that nitric
oxide mediated, CB-mediated and other receptor mediated signalling is
important in neuroglial communication. Although there are receptors
that respond to ATP (such as the polymodal TRPV1 for example),
extracellular ATP is usually a signal of damage. I realize that there
are a large number of gap junctions between astrocytes, but ATP
wouldn't typically be an important intracellular signal such as cAMP
or Ca2+.

and that that
evidence points to/supports several functional cognitive enhancments in
which glia are involved over and above their normal scenarios (e.g.,
Einsteinn's brain).


Explain please.

--
kj
 




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