Explanation of Adrenarche: Human Evolution

James Howard jmhoward at sprynet.com
Fri Sep 3 08:57:14 EST 1999

DHEA, Growth of the Brain, and Human Evolution: Support of a Theory of Human

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

The phenomenon called “adrenarche” has not been fully explained.  It has
been well described.  “Another event that occurs in humans at the time of
puberty is an increase in the secretion of adrenal androgens.  [The
predominant adrenal androgen is dehydroepiandrosterone (DHEA).]  The onset
of this increase is called adrenarche.  It occurs at age 8-10 years, without
any change in the secretion of cortisol or ACTH.  It may be due to a change
in the enzyme systems in the adrenal so that more pregnenolone is diverted
to the androgen pathway.”  “Review of Medical Physiology,” Sixteenth
Edition, Appleton & Lange, 1993, pages 382-383.  Now, my work suggests
another explanation of why adrenarche occurs, for which I just found
potential support.  For anyone interested, please find my chart of DHEA
production during the human life span in my explanation of human evolution
at http://www.naples.net/~nfn03605/.  It is the first chart, and I explain
my hypothesis regarding adrenarche there.

When we are born, our levels of DHEA are very high.  This is rapidly
followed by a decline in DHEA to very low levels, which begin to rebound,
starting around age five to six.  The levels then increase until around age
twenty, followed by a slow decline to very low levels in old age.  My
explanation is that DHEA is used by every tissue for transcription and
duplication of DNA.  Therefore every tissue competes for a limited supply.
I think the brain evolved to use DHEA in very large amounts, at the expense
of the other tissues.  Hence, the brain grows much larger and more complex,
relative to other tissues.  We are in the line of creatures that express
this phenomenon more than other creatures.  Now, I will explain adrenarche.
I think the decline in measurable levels of DHEA is the result of use of
DHEA by the brain for growth.  This use of DHEA by the brain, along with use
of DHEA for body growth, causes the dip in levels of DHEA that occur just
prior to adrenarche.  As the brain finishes growth, the levels of measurable
DHEA begin to increase.  (This dip in DHEA is much greater in humans than
chimpanzees, which express a much larger dip than monkeys.)  Further in my
explanation of human evolution is a chart that compares DHEA during the life
span of a monkey, chimpanzees, and humans (also at my page).  Adrenarche
increases proportionally to the size of the brain.  This is further
supported by the citation, I just found and which is just below.  (For those
interested, I invite you to read my explanation of human evolution,
including adrenarche, at the page address mentioned above.  Also, you might
be interested in finding the complete abstract of this article at the
National Library of Medicine’s search engine called “pubmed.”  “DHEAS” is
the background source of DHEA in blood.)

“These studies provide evidence of mechanisms by which DHEA and DHEAS exert
biological actions, show that they have specific functions other than as sex
steroid precursors, mediate their effects via non-classic steroid hormone
receptors, and suggest that their developmentally regulated synthesis in
vivo may play crucial and different roles in organizing the neocortex.”
Compagnone NA and Mellon SH, Proceedings of the National Academy of Science
USA 1998; 95: 4678.

More information about the Bioforum mailing list