Explanation of the Flynn Effect


Copyright 1997, 2010 by James Michael Howard.


 (Added April 26, 2010: Maybe the major part of my explanation of how DHEA is used by the brain is that various parts of the brain compete for DHEA. As is well known now, in the U.S. and maybe elsewhere, the frontal lobes develop last. As the brain is exposed to increased testosterone in utero, androgen receptors are formed which are accessed by DHEA. This effect increases androgen receptors which cause the competition for DHEA. If the brain exhibits increased androgen receptors in parts of the brain other than the frontal lobes, then these areas will exhibit increased competition for DHEA during childhood and adolescence and increase in function. This competition will reduce final growth and development of the frontal lobes while increasing growth and development of other areas because of competition. I think this is why we are seeing increased lack of impulse control in our youth. (The frontal lobes control lower brain impulse control.) I think the same mechanism causes the Flynn Effect. Again, I suggest this is caused by this same mechanism, that is, while the frontal lobe is reduced in competition for DHEA, other areas are increasing. Memory is improved in the Flynn Effect. An improvement in one area of the brain may indicate that another may exhibit a decline. This is why they Flynn Effect may be increasing simultaneously with decreasing frontal lobe development. Our populations are gaining in one area while we loose abilities in the very areas that make us human. Humans are characterized by impulse control. (Of course, I think this ability is being reduced by the secular trend.)

Some people think the Flynn Effect is a positive finding. I do not think so. I think it indicates that we are being adversely affected by the increased exposure to testosterone. We are losing the ability to control impulses because of increasing maternal testosterone which is producing many adverse phenomena, such as increased morbidity, and the Flynn Effect. The Flynn Effect should be viewed as a negative finding.)

The Flynn Effect refers to an increase in IQ that occurs along with the secular trend. The secular trend is the increase in size, height and weight, and the earlier onset of puberty in children. The Flynn Effect is mainly an increase in scores on "non-verbal tests." The overall effect is primarily due to increases in the lower half of the IQ distribution, but it also occurs in the "gifted," or those who score 1400 or more on the SAT. The Flynn Effect is a worldwide phenomenon. (It occurs in all socioeconomic groups.)

I suggest the Flynn Effect is due to rising testosterone. The effect is small; perhaps 15 points in two generations. I suggest that two kinds of increases in hominid brain size have occurred in human evolution. One, that causes only slight increases in brain size, I attribute to increasing testosterone in hominids. This is the small increase noticeable in the early hominids. This is the increase I think is due mainly to the increases in testosterone that started separating us from the other primates. (Human males and females produce more testosterone than chimpanzee males and females.) The main increase in hominid brain size, I suggest, is due to the effects of the hormones, DHEA and melatonin that occurred as hominids moved away from the equator. (Please read my explanation of human evolution at this site for more detail.) The effects of these two hormones, according to my theory, have to occur away from the equator, and this is where the fossil evidence, north and south, shows the main increases in brain size. The increase in testosterone will cycle through hominids, i.e., testosterone will periodically rise in humans. It will produce some dramatic effects, but one, I suggest, is a slight increase in nonverbal abilities of the brain that will cause slight increases in overall IQ scores. To explain this, I am including part of my "letter to the editor," in The Morning News of Northwest Arkansas, May 14, 1995, regarding math and English levels in American schools. This was generated in response to findings that "reading proficiency is down in virtually 40 states ...and significantly down in 10." The math scores were up lightly; this is the Flynn Effect in the U.S., as of April, 1996. The increase in testosterone causes the slight increases in nonverbal abilities, while it causes decreases in verbal abilities. This letter explains the basics of my explanation of the mechanism that produces the Flynn Effect.

"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 demonstrated 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 to growth to left. The right side is used more for mathematical and spatial thinking, therefore, on average, boys outperform 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 mathematical 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 looses 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, 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."