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