Common Evolutionary Mechanism in Insects and Humans

jamesmichaelhoward at my-deja.com jamesmichaelhoward at my-deja.com
Wed Apr 26 10:02:13 EST 2000


A Common Mechanism of Evolution in Insects and Humans

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

The findings of Lewis, et al., regarding gene regulation in insects,
Proc. Natl. Acad. Sci. USA, Vol. 97: 4504-4509, April 25, 2000, may be
used to support a new explanation of evolution that may also have
functioned in human evolution.  That is, Lewis, et al., possibly
demonstrate competition among genes for a limited amount of gene
activating molecules (hormones).  One tissue, or gene, uses these
molecules at the expense of another, therefore, growth and development
of one structure occurs at the expense of development of another
structure.  The activity and presence of gene activating (regulating)
molecules, such as hormones, may explain the findings of Lewis, et al.
In insects, homeotic genes direct development of segments and
appendages that develop thereupon.  The gene, Distal-less (Dll)
promotes appendage production, and the function of Dll is repressed by
Ultrabithrorax (Ubx) and abdominal-A (Abd-A) in Drosophila
melanogaster.  In their test animal, Tribolium, Lewis, et al., found
that “Abd-A, but not Ubx, represses early expression of Dll in the
embryonic abdomen.”  Since “in many species, appendage-like structures
are present on abdominal segments in embryonic and juvenile stages,”
and since possibly there is an abundance of “gene regulating molecules”
during embryonic development, with less available in the juvenile
stage, gene regulation could be simply accomplished by a limited supply
of gene activating molecules.  Therefore, during insect development,
sequential gene activation would be accomplished by genes becoming
activated and using more gene regulating molecules (hormones) than
genes already functioning.  The result would be the closure of some
genes and activation of other genes which sequester more hormones for
their use.  Evolution could occur rapidly with this mechanism.  I
suggest genes that sequester more hormones for their use will quickly
be selected by evolution, because their increased use of a limited,
useful supply of hormones would readily identify increased survival
value.  This would quickly increase the rate of evolution, since genes
that do not increase survival advantage and take extra hormones would
quickly interrupt survival.  I suggest the major accomplishment of this
sort of gene selection was increased nervous tissues.  Nervous tissues
nets of early evolution increased at the expense of other structures.
Therefore, the evolution of nervous tissues directly, and
simultaneously, caused changes in the body of animals.  Those which
survived, did so with advanced bodies and better nervous development.

A key event in human evolution is gracilization of the cranial and post-
cranial skeleton along with increases in brain size. (gracilization is
the reduction in size and robustness of the skeleton that occurred
simultaneously with the increase in brain size, especially in later
hominids.)  It is my hypothesis that this occurred as a result of the
same mechanism I explained above.  At its most basic, I suggest
gracilization in hominids occurred as a result of use of the hormone,
dehydroepiandrosterone (DHEA), by the brain at the expense of the
body.  (DHEA is both manufactured by, and imported into, the brain from
blood (Acta. Paediatr., 1999, Suppl. 88, 78-80) and DHEA directly
affects bone formation (J. Endocrinol. 1998, 157: 433-42).  I suggest
that the human brain increased in growth and development at the expense
of bone development during hominid evolution.  The brain used DHEA at
the expense of the body.  That is, in the same way that some genes
reduced availability of insect hormones for use by other genes, the
hominid brain increased its use of DHEA for growth and development at
the expense of growth and development of bone tissues.  The same
mechanism of competition for gene activating molecules results in
changes in animals that eventually become different species.  This
explanation may also account for the relatively rapid changes in
animals that have occurred throughout evolution.


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