Repost: Hominids and Teeth ...yes, testosterone

James Howard (phis@sprynet.com)
Wed, 30 Oct 1996 10:59:37 GMT

Hominids and Teeth ...yes, testosterone

I have suggested to this group that the cause of hominid evolution is
increases in testosterone. I have explained this and given a number of
demonstrations of how increases in testosterone cause the various
characteristics of Homo. This group has been discussing increased tooth
enamel in hominids. Therefore, this post is designed to demonstrate that
this characteristic is, also, due to the increases in testosterone.

First, I want to explain, again, that I think testosterone has increased
relatively continuously to produce Homo sapiens sapiens. We have not
reached the size in teeth, etc., characteristic of some some earlier hominids,
such as the robust Australopithecines, that, I think, exemplify extremes of
testosterone. Our brains produce many testosterone receptors that literally
absorb testosterone at the expense of other organs, such as teeth.
Therefore, our teeth are not as large as these robust characters, because
their brains were small. (I have explained the relationship of the brain to
tooth size earlier in this group.) Once a "feed and breed" situation is
established, testosterone will increase to the point that it reaches too high
levels. I have explained, also at this group, that too high testosterone
increases infection rates, increases infant mortality, and reduces sperm
counts, all of which will lead to extinction, especially in the environment of
the extinct "high testosterone" hominids. The point is that this increase in
testosterone follows a cycle. When a lot of food it present, it makes the
increase in testosterone occur faster. I have explained that I think this is
currently occurring in the U.S. It can be seen in changes in tooth enamel,
currently in the U.S., and I think this is due to increases in testosterone.

A lot of the posts to this newsgroup agree with the hypothesis that extremes
in diet caused the pronounced tooth size and thick enamel of the early
hominids. The argument is that a grainy, fibrous diet resulted in this
increase in tooth size. In the following quotation, please note that "enamel
hypoplasia" is currently being reduced in Cleveland, Ohio. That is, tooth
enamel is increasing in thickness. If the current hypothesis is correct, this
would mean that the diet in Cleveland, Ohio, is increasing in grain and fiber.
While there is a current movement to increase fiber in our diet, the study
was done in 1978, long before this trend. I suggest that the diet covered
during this study changed from relatively free of fiber to very free of fiber.
(The investigators offer an explanation, and it may be the answer if the
robust Australopithecines had "improved nutritional conditions" and few
"childhood diseases.") I think this increase in tooth enamel thickness in
Cleveland, Ohio, is due to the secular trend, i.e., an increase in testosterone.

El-Najjar MY et al., "Prevalence and Possible Etiology of Dental Enamal
Hypoplasia" Am J Phys Anthropol 1978; 48: 185

"Two hundred black and white adult human skeletons and 200 living black
and white children from the greater Cleveland area were examined for
evidence of enamel hypoplasia. Enamel hypoplasia, present in varying
expressings (pits, lines and grooves), was found to be more prevalent in
both skeletal samples, than in the living groups. In the majority of cases, sex
differences between white and black males and females through time and
space are highly significant for all tooth catagories. Regardless of the
mechanisms behind it, prevalence of enamel hypoplasia for both white and
black group has significantly declined through time. No evidence suggesting
specific etiologies responsible for enamel hypoplasia can be found. In the
majority of previously published reports, the etiology is still idiopathic. The
reduction in the prevalence of enamel hypoplasia in the groups examined
through time may be related to improved nutritional conditions and the
elimination or decline of childhood diseases that have been implicated in this
condition."

The literature is sometimes not certain whether the increase in hominid tooth
characteristic is due to increased enamel or increased dentin, or both. In the
following quotations, the general direction is in the same for increases in
either, or both, enamel and dentin in maleness and individuals of increased
testosterone.

This quotation demonstrates that enamel and dentin are both increased in
"47,XXY males.

Alvesalo L et al., "Enamel Thickness in 47, XXY Males' Permanent Teeth"
Ann Hum Biol 1985; 12: 421

"Enamel thickness of the maxillary permanent central incisors and canines
in 14 47,XYY males, their male and female relatives and population-control
males and females were determined from radiographs. The results
indicated, although not fully unambiguously, that the thickness of enamel
and that of 'dentin' (distance between mesial and distal dentino-enamel
junctions) are increased in the teeth of 47,XYY males compared with normal
controls."

Individuals of the 47, XXY genotype produce more testosterone than normal
genotypes.

Schiavi RC et al., "Pituirary-gonadal Function in XYY and XXY Men
Identified in a Population Survey" Clin Endocrinol (Oxf) 1978; 9: 233

"The XYY men had significantly higher plasma concentrations of LH, FSH
and testosteroe than matched controls."

In a normal population the dentin is "significantly thicker" in males than
females.

Stroud JL et al., "Sexual Dimorphism in Mesiodistal Dentin and Enamel
Thickness" Dentosmzxillofac Radiol 1994; 23: 169

"The results showed significant sex differences (p<0.01) in mesiodistal
diameter favouring mles over females. Dimorphism was more pronounced
for the molars than premolars. Enamel thickness, which is 0.4-0.7 mm
greater for the molars than premolars, shows no significant sex differences.
Dentin is significantly thicker in males than females, and is 3.5-4.0 mm
thicker in molars than premolars. It is concluded that sexual dimorphism in
mesiodistal tooth sizes is due to differences in dentin thickness and not
enamel thickness."

I suggest that the increased enamel and/or dentin in the teeth of hominids is
due to the increased testosterone in hominids. (The teeth of Neandertal are
produced by a variation of this mechanism, caused by increased
testosterone and DHEA in Neandertals.)

James Howard