The Effects of Brain Growth on the Long Bones of Hominids. A Possible Response to "Born to Run." SUPPLEMENTAL

James Michael Howard jmhoward at anthropogeny.com
Thu Nov 18 17:33:08 EST 2004


The Effects of Brain Growth on the Long Bones of Hominids.  A Possible
Response to "Born to Run."  (Endurance running and the evolution of
Homo; Nature 432, 345 - 352 (18 November 2004);
doi:10.1038/nature03052) SUPPLEMENTAL 

Copyright 2004, James Michael Howard, Fayetteville, Arkansas, U.S.A.

Long bone growth may be determined by the speed of growth.  If the
brain is competing for growth with the long bones, then Homo sapiens
will have longer bones because of the longer time to puberty.  This
may give the "appearance" of being born to run because all aspects of
our growth are affected by the same competition.  That is, we have
long bones and associated structures because of our brains, not
because of environmental effects.  The bodies, so-equipped, are better
at endurance running.

For example, the long bones of "Down's syndrome" are shorter than
normal (Am J Obstet Gynecol. 1989 Nov;161(5):1174-7).  If the brain is
not competing efficiently, then long bone growth is shortened by the
more rapid growth of these bones.  The bones grow faster and finish
development faster.  (I understand there are variations to this
hypothesis.  If the brain and long bones are competing for the same
thing and that "thing" is reduced then both will not develop well,
etc.)  

I suggest the long time necessary for our brain growth and development
may produce the bodies that have been interpreted as "born to run."
Once that growth and development of our brains nears finalization,
then the competition shifts towards that of the body, re: long bone
growth and development, and the bones suddenly develop rapidly and
also finish growth, after the brain.  That is, once the brain reduces
competition, the long bone growth accelerates and quickly finishes.

SUPPLEMENTAL:  The following findings may support my hypothesis; the
citation containing these findings follows just below.  Again,
basically I submit that brain growth and development competes with
limb growth and development (length).  During brain growth, limb
length may be extended because of longer period of growth.  That is,
the limb grows long and thin rather than short and thick.  This effect
should affect limb growth according to brain growth until puberty when
the brain finalizes growth and development.  In finding number one,
this may be seen, that is, taller children indicates longer brain
growth until puberty and shorter indicates a shorter time for brain
growth until puberty.  The ratios are extended in the taller children.

1. It was found that the ratios of leg length to height, leg length to
arm span, and arm span to height were bigger in taller children in the
same age group than the shorter ones in both sexes. 

In number two, the older the child, the longer the period of brain
growth.  Hence, the ratios are bigger in older children.

2. All the ratios were bigger in older children in the same percentile
than the younger ones in both sexes, showing that the growth rates of
leg length and arm span were bigger than that of height in general. 

In number three, I suggest shorter children reach puberty earlier so
leg length is shorter until puberty.  Taller children, reaching
puberty later exhibit longer length because of extended brain growth.

3. However, growth of leg length is faster in shorter children than in
taller children until the onset of puberty, after which growth of leg
length in taller children is faster than in shorter children. 

In number four, the rapid growth of leg length from birth to 2 years
represents the extended growth in length because this is a period of
rapid growth and development of the brain.  The growth spurt during
the pubertal period represents the switch over in competition towards
that of limb growth as the brain finalizes growth.  This generates a
rapid growth and finishes the bone growth.

4. The first and most rapid growth of leg length is seen from birth to
2 years, the second growth spurt is seen during the pubertal period. 

The taller children exhibit the rapid leg growth as puberty occurs in
number five.

5. An exceptional increment in leg length between ages from 10 to 15
is also noted in taller children. 

Number six provides information that leg and arm length are also
competitive.  In the tallest children, the reduced impact of puberty
allows a slightly increased time of the rapid growth in the arm as the
leg has already grown at this period, then increasing the competition
for growth by the arm.  Short children, because of the increased
impact of puberty have a shortened period of rapid growth which also
affects and reduces arm growth.

6. After puberty, arm span grows faster than height until 17 years of
age in the tallest male child, and taller children have longer arm
span than height, while arm span in the shortest children never
exceeds height.

I have been told that arm length is longer in some apes.  Brain growth
and development in apes is reduced compared to humans so the period of
increased competition for growth by some of the apes will be extended,
therefore, increasing arm length to leg length.  That is, ape brain
growth competes with the hind limbs in some apes and, when finishing,
allows increased arm growth until the growth and development periods
are complete.

Ann Hum Biol. 1995 Sep-Oct;22(5):443-58.	

Correlations among height, leg length and arm span in growing Korean
children.

Yun DJ, Yun DK, Chang YY, Lim SW, Lee MK, Kim SY.

Yonsei University College of Medicine, Seoul, Korea.

A cross-sectional study was performed to find out if any specific
correlations exist among height, leg length and arm span in growing
Korean children. Height, leg length and arm span were measured in
10,322 healthy children (4740 males and 5582 females). Computed ratios
of leg length to height, leg length to arm span and arm span to height
for the 3rd, 25th, 50th, 75th and 97th percentiles were made. It was
found that the ratios of leg length to height, leg length to arm span,
and arm span to height were bigger in taller children in the same age
group than the shorter ones in both sexes. All the ratios were bigger
in older children in the same percentile than the younger ones in both
sexes, showing that the growth rates of leg length and arm span were
bigger than that of height in general. However, growth of leg length
is faster in shorter children than in taller children until the onset
of puberty, after which growth of leg length in taller children is
faster than in shorter children. The first and most rapid growth of
leg length is seen from birth to 2 years, the second growth spurt is
seen during the pubertal period. An exceptional increment in leg
length between ages from 10 to 15 is also noted in taller children.
After puberty, arm span grows faster than height until 17 years of age
in the tallest male child, and taller children have longer arm span
than height, while arm span in the shortest children never exceeds
height.





More information about the Neur-sci mailing list