Intended for healthcare professionals

Rapid response to:


Education, income inequality, and mortality: a multiple regression analysis

BMJ 2002; 324 doi: (Published 05 January 2002) Cite this as: BMJ 2002;324:23

Rapid Response:

Another Possible Explanation of Dr. Muller's Findings

I suggest another hypothesis may explain "Education, income
inequality, and mortality: a multiple regression analysis," BMJ 2002; 324:
23. Excessive testosterone may be the cause. That is, failing to
graduate high school and shortened life span may be coincident
consequences of high testosterone.

It is my hypothesis that human evolution is driven by increases in
testosterone ("Androgens in Human Evolution. A New Explanation of Human
Evolution," Rivista di Biologia / Biology Forum 2001; 94: 345-362). I
suggest all hominid characteristics are directly influenced by increasing
testosterone. Periodically, however, where circumstances are very
favorable to reproduction, testosterone increases too rapidly. My work
suggests this causes problems in increased infection rates, lowered sperm
counts, etc. These circumstances may have produced the “bottleneck in
hominid populations” which I connect with “Mitochondrial Eve” and
excessive testosterone, which was overcome by mutations controlling sperm
production, which I connect with “Y Chromosome Adam.” (“Mitochondrial Eve,
Y Chromosome Adam, Testosterone and Human Evolution,” accepted for
publication by Rivista di Biologia / Biology Forum.) Populations of high
testosterone individuals sometimes experience very negative consequences.

Within modern populations, I suggest these periodic, rapid increases
in testosterone within populations produce the “secular trend,” which is
real and vigorous at this time in the U.S.A. (“Secular Trends in Height
Among Children During 2 Decades. The Bogalusa Heart Study,” Archives of
Pediatric and Adolescent Medicine. 2000; 154: 155-161). The secular trend
is the increase in size and earlier onset of puberty. The phenomena
Muller examined are current problems, i.e., byproducts of the secular
trend. Testosterone is connected with numerous conditions Muller
describes as “economic resource deprivation, risk of occupational injury,
and learnt risk behaviour.” For example, domestic violence is connected
to testosterone: “Testosterone levels were significantly associated with
levels of both verbal aggression and physical violence self-reported by
the men.” (Psychoneuroendocrinology 2000; 25:721-39), learning
disabilities: “The matched analysis further substantiated the association
between testosterone secretion and learning disabilities. Thus, it is
possible that some learning disabilities may be associated in part with
abnormal testosterone levels.” (Physiol Behav 1993; 53: 583-6), adolescent
smoking: “In this study, salivary testosterone was positively associated
with cigarette smoking among 201 subjects 12-14 years of age.” (J Behav
Med 1989; 12: 425-33), impulsive behavior: “…the results of this study
support a positive relationship between testosterone and impulsivity.”
(Physiol Behav 2001; 73: 217-21), and infection rates: “…male gender was
significantly associated with an increased incidence of pneumonia after
injury…” (J Trauma 2001; 50: 274-80). I suggest the presence of
testosterone also accounts for phenomena described by Dr. Muller.

In the U.S.A. blacks males disproportionately fail to graduate high
school and exhibit “economic resource deprivation, risk of occupational
injury, and learnt risk behaviour.” I suggest this is due to the fact
that black males produce significantly more testosterone than other groups
vis-à-vis females and white males. “Mean testosterone levels in blacks
[males] were 19% higher than in whites [males], and free testosterone
levels were 21% higher. Both these differences were statistically
significant.” (J Natl Cancer Inst 1986; 76: 45-8). Black boys were
affected most by the secular trend in the Bogalusa Heart Study.

I suggest increases in testosterone within certain groups may also
explain Dr. Muller’s findings.

Competing interests: No competing interests

15 January 2002
James M. Howard
1037 North Woolsey Avenue, Fayetteville, Arkansas 72701-2046, U.S.A.