Response to Olson, Barnard, and McPherson

[James Howard]

Response to Howard Olson, Steve Barnard, and Ron McPherson
James Howard

Howard Olson, MA wrote:
"First of all, the brains of men and women are comparable when you 
consider the  body size to brain size ratio. This is a well known fact 
of paleoneurology.  Secondly, testosterone is Not the only anabolic 
steroid in the human body and there may well be an analogous effect from 
another steroid or even a peptide (such as GH ) in the female.

 BTW, are you aware that testosterone is metabolized to estrogen BEFORE 
it reaches the nuclei of target cells? Surely that throws a monkey 
wrench into the simple reductionist model you propose for male 
superiority."

James Howard responds:
Below this response to Mr. Olson, I have included the publication which 
caused me to post my message.  It includes this statement of part of the 
findings: "Sex and age were the main determinants of the total number of 
neurons in the human neocortex, whereas body size, per se, had no 
influence on neuron number."  The authors disagree with your first 
statement that "the brains of men and women are comparable when you 
consider the body size to brain size ratio."  Now, I have to admit to 
some sloppiness here; I should have entitled my message "Male brains 
have slightly more neurons than Female Brains."  In fact, the report 
states that the difference is 16%.  Additionally, in male humans, 
testosterone is produced in significant quantities once in utero, again 
neonatally, and then, in about twice these amounts, beginning at puberty 
(Fig. 23-19, page 392, Review of Medical Physiology, W.F. Ganong, 
Appleton & Lange, 1993).  As you know, head size is pretty much 
determined during fetal development and within the first year 
postnatally; the time at which the first two increases in testosterone 
occur.  With this in mind, consider this: "Head circumference is larger 
at birth for males (36 ± 1.97 cm) than for females (34 ± 1.6 cm).  Males 
continue increases in head growth over females so that at 1 year of age 
head circumference values are 39 percent over birth values for males and 
35 percent for females." Sexual Dimrphism in Homo sapiens A Question of 
Size, edited by Roberta L. Hall, Praeger Publishers, New York, 1982, 
pages 281 - 286.  This is not due to thicker cranial bones in males; on 
page 281, of the same text, Hall states: "In addition to these 
measurements, sex difference in the pace of osseous maturation is 
evident at 30 fetal weeks.  The female average is 2 weeks beyond the 
male in bone age at the time of birth and is 8 weeks ahead by 1 year of 
age."  Also, on pages 286- 287, Hall suggests a connection of 
testosterone with this difference in growth rates.  "In sum, the basic 
sexual dimorphic trend is the faster late fetal and early infancy growth 
rate of the male as compared to that of the female in length, weight and 
head circumference.  Sex differences persist in childhood but with a 
reduced velocity in growth rate until the advent of adolescence.  The 
early acceleration of male growth may be the consequence of 
testosterone, which is at levels of 250mg/100ml in the serum of the 
infant male in the first few postnatal months."

I absolutely agree with your second point.  It is my theory that 
testosterone works by directing increased use of the adrenal androgen, 
dehydroepiandrosterone (DHEA), to use by DNA in tissues that absorb, or 
acquire, via cell receptors, testosterone.  So, I agree that other 
androgens are involved.  Also, my theory suggests that DHEA acts with 
specific proteins to activate specific areas of DNA.  I consider growth 
hormone to be, perhaps, the most important of these hormones.

I am aware that testosterone is converted to estradiol.  This does not 
"throw a monkey wrench into the simple reductionist model you propose 
for male superiority."  (The word superiority is not in my original 
post; any interpretation of my post to promote male superiority is your 
opinion.  Also, in science, it is customary to first consider the 
simplest explanation of anything.  This is the law of parsimony.)  As a 
biologist, I try to view everything in terms of evolution.  As you 
probably know, our bodies are considered to be "female," until acted 
upon by testosterone.  I suggest the real advantage that occurred when 
one of the X chromosomes lost one of its arms was the production of 
testosterone.  (Here I deserve a "Well, duh!)  However, let me add my 
explanation.  If this new "sex" could produce testosterone, which is a 
precursor to estradiol production, then an advantage develops.  I 
suggest that advantage is that the testes, formally ovaries, produce 
this precursor more so than the estradiol-producing ovaries.  The testes 
produce more of the precursor than the final product.  So, "males" 
produce more testosterone than females.  (Again, well, duh!)  Not only 
did this transformation start the evolution of the egg into the sperm, 
it had another effect which has to do with my explanation of evolution. 
 I think what this boils down to is that the increased production of 
testosterone is an increase in the production of the precursor to 
estradiol.  As you pointed out, testosterone is converted to estradiol. 
 Almost all cells can convert one steroid hormone into another.  If the 
testes produce an increased supply of testosterone, then these cells can 
produce increased estradiol from the increased precursor, and they are 
not dependent upon an increased supply of ovarian estradiol near 
ovulation.

This brings me back to my point.  Testosterone, by the method I have 
just developed, could activate neuronal growth, development, and 
function, by increasing, ultimately, the supply of estradiol.  
Therefore, testosterone will increase neuron number and activity.  This 
explains the increased numbers of neurons in males and the increased 
activity of their sex drive.  It is known that testosterone stimulates 
sex drive in male and female humans, and female gorilla sex activity 
increases on the day their testosterone peaks.  This is an explanation 
of how sex evolved.  Testosterone evolved to increase reproduction.  It 
just happens that it stimulates neuron growth, development, and 
activity.  Therefore, testosterone has a direct effect on evolution of 
the brain.  Males produce more of it, therefore, males have about 16% 
more neurons.

(In anticipation of one of your responses to the foregoing, let me point 
out that the levels of testosterone have been found to have no 
connection with human male homosexuality.  However, DHEA is, on average, 
low in male homosexuals.  Since I suggest that testosterone activates 
genes that use DHEA, the normal testosterone levels in male homosexuals 
would not be able to fully stimulate the growth of the nuclei of the 
brain concerned with sexual direction.  Hence, reduced DHEA in utero, 
this could explain the underdeveloped size of the sexually identified 
brain nuclei in male homosexuals.)

J Comp Neurol 1997 Jul 28;384(2):312-320, "Neocortical neuron number in 
humans: effect of sex and age," Pakkenberg B, Gundersen HJ

"Modern stereological methods provide precise and reliable estimates of 
the number of neurons in specific regions of the brain. We decided to 
estimate the total number of neocortical neurons in the normal human 
brain and to analyze it with respect to the major macro- and 
microscopical structural components, to study the internal relationships 
of these components, and to quantitate the influence of important 
physiological variables on brain structure. The 94 brains reported 
represent a consecutive collection of brains from the general Danish 
population. The average numbers of neocortical neurons were 19 billion 
in female brains and 23 billion in male brains, a 16% difference. In our 
study, which covered the age range from 20 years to 90 years, 
approximately 10% of all neocortical neurons are lost over the life span 
in both sexes. Sex and age were the main determinants of the total 
number of neurons in the human neocortex, whereas body size, per se, had 
no influence on neuron number. Some of the data presented have been 
analyzed by using new mathematical designs."

Steve Barnard wrote:
"It's also recently been determined that men's brains have more neurons 
that women's -- something like four billion more, give or take a few. So 
what?"

James Howard responds:
Please read my response to Howard Olson; that is so what.

Ron McPherson wrote:
"First of all, the brains of men and women are comparable when you 
consider the  body size to brain size ratio. This is a well known fact 
of paleoneurology. Secondly, testosterone is Not the only anabolic 
steroid in the human body and there may well be an analogous effect from 
another steroid or even a peptide (such as GH ) in the female.

:       BTW, are you aware that testosterone is metabolized to estrogen 
BEFORE it reaches the nuclei of target cells? Surely that throws a 
monkey wrench into the simple reductionist model you propose for male 
superiority.

Exactly correct.  Testosterone and estrogen are interconvertible in 
brain and either hormone functions in multiple nuclei both during 
development and adult function.  The body size to brain ratio comment is 
also true but more importantly, as H. Jerison pointed out years ago 
(this brain size observation is much older than the current hype) the 
amount of cortex between men and women is comparable.  Thus men and 
women have about the same amount of cerebral cortical surface area.  
Jerison says that the women have increased invagination so that more 
cortex is folded into a smaller cranium.

So meaningful differences between the brains of men and women (outside 
of the sexually dimorphic nuclei of the medial preoptic hypothalamus) 
remain undiscovered."

James Howard responds:
The only thing I can say to you is please read my response to Howard and 
the quotation above.