Mechanism of intelligence

James Howard (
Mon, 19 Aug 1996 17:51:41 GMT

This is my "letter to the editor," printed May 14, 1995, in "The
Morning News of Northwest Arkansas." It is a very short explanation
that suites the information printed in the newspaper regarding another
measurement of learning skills in the nation's school. Since this
group has been considering the influence of sex on intelligence, I
thought some of you may be interested.

"The editorial of April 29, page 18A, 'The Decline in Reading,' had
bad news and good news. The bad news is that 'reading proficiency is
down in virtually 40 states ...and significantly down in 10.' The
good news is 'that math scores are on the rise.' The editorial says
that 'educators almost unanimously agree that' teachers aren't asking
enough of their students. Their conclusion doesn't make sense; it
would take a major conspiracy to cause a nationwide drop in reading
skills. Ironically, a rise in math scores, along with a decline in
reading scores, may both signal something else is happening, perhaps
beyond the reach of the best teachers.

It is generally accepted that the two sides of the brain (cerebral
hemispheres) interact but basically perform different functions. The
things we call reading and writing are usually controlled by the left
half, mathematical things and spatial abilities are usually located in
the right half. Because of this divergence in function, boys are,
generally but not always, better in math than girls. My work suggests
a reason for this that is directly connected to the changing reading
and math scores.

The left hemisphere finishes growth a little after the right. My work
suggests brain growth is particularly dependent on the hormone DHEA.
(DHEA in extremely small quantities stimulates formation and growth of
the brain cells primarily used in thinking, neurons.) Therefore, the
left hemisphere depends on a continued supply of sufficient DHEA for
final growth. All tissues, especially the brain, compete for DHEA.
The hormone testosterone increases use of DHEA by testosterone target
tissues, which also includes parts of the brain. Boys produce more
testosterone than females so there is less DHEA, on average, for left
hemisphere growth. In animals studies, it has been demonstrted that
testosterone actually reduces development of the left hemisphere
(Behavioral and Neural Biology 1988; 49: 344). Therefore, boys, on
average, have an increased ratio of right hemisphere growth to left.
The right side is used more for mathematical and spatial thinking;
therefore, on average, boys out-perform girls in these areas.

If you want to be a good mathematician, you might be tempted to want
more testosterone. In tests of spatial and mathematicl reasoning,
males with high testosterone score much worse than those with low
testosterone. High testosterone increases lower brain growth and
development at the expense of even the right hemisphere. That is, in
high testosterone, even the right hemisphere loses in the competition
for DHEA.

I have suggested in past letters to this paper that testosterone is
rising in this society. Most people see it in the 'secular trend,'
that is, that boys and girls are getting bigger and reaching puberty
earlier. If testosterone is rising, it not only will affect the size
of our children, but it will also affect their brains. That is, as
testosterone increases it will decrease the ratio of left hemisphere
to right. This will be seen, on average, as a decline in reading
ability and an increase in math abilities. In areas where
testosterone is very high, reading and math scores should both
decline. The thing that worries me most is that one of my references
points out that 'the left hemisphere also seems to be the seat of
analytical thinking...' According to the National Assessment of
Educational Progress, we may be seeing a real, and in some areas
already significant, decline in functions of the left hemisphere."

James Howard