The dropping age at menarche was one example I chose in an earlier blog of the physical effects of civilization on the "savage metabolism" - part of the story of The Tribal Imagination. Civilization's effects on the savage mind start with its effects on the Paleolithic body. Records exist from Scandinavia since about 1840, and show that girls then hit puberty at about 16 or 17. Now they can start as early as 7. In Germany researchers note that in 1860 the average age at menarche was 16.6 years, in 1920 14.6, in 1950 13.1 in 1980 12.5, while in 2010 the average had dropped to 10.5. The trend is similar for all Western developed nations. Figures from the developing world show a different picture with the average for 15 to 17 years, although the more developed the country, the greater the drop.

The figures are very familiar, but the raw figures do not tell the whole story. I have been interested in this problem since working with John Tanner and his associates at the University of London in the 1960s. His Growth at Adolescence (1955) was a milestone: see also his Human Growth (1960), and among other things he found the spurt in testosterone at puberty that shoots boys into rapid growth and sexual maturity, and that does not seem to have been affected. It is much the same now as it was in the past or is in the developing world. What is it with the "secular" downward trend in girls?

An excellent website suitably called "average age at menarche" from the Museum of Menstruation and Mental Health is good with the details and the graphs. I think the answer is hidden in their graphs. They cite the following as possible causes: "better nutrition" leads the field followed by improved environment; smaller families; natural selection; climate warming; declining disease; obesity; sedentary lifestyle; chemicals; hormones; sex on TV and of course the usual stress at home. There is no conclusive data to prove any of these. But they have a graph, actually from a paper by Tanner and an associate, that shows that age at menarche in Finland, Poland, Romania, India and South Africa is up to two years later in rural than in urban areas.

There is a clue here that was taken up by researchers in the seventies but that seems to have been forgotten since, and never appears in the popular accounts like the one in USA Today. The whole "better nutrition" and "fat in the diet" theory failed when Scandinavian data showed that country girls, well fed and plump on the butter, cheese and cream, still hit menarche much later than their urban counterparts. And the difference had become intensified once artificial lighting was introduced to cities and towns (gas light and then electricity.) The country girls were still governed by the circadian rhythms of the natural light cycle - by available daylight. Their town cousins on the other hand, had daylight extended by artificial light at both ends, resulting a day that was often twice as long in light intensity as the natural day - particularly in the winter.

What has this to do with early puberty? The suggestion was that it lay in the pineal gland. This small gland in the brain, lying between the two hemispheres (and shaped like a tiny pine cone, hence its name) is large in children and calcifies with age. Researchers at Yale in 1958 discovered that the major product of the gland was a derivative of tryptophan, a hormone they called melatonin, which is stimulated by darkness and inhibited by light. One function of this hormone seems to be to hold back sexual development in females. Female rats who either had their pineal glands removed or were subjected to constant light, had abnormally early development of the ovaries. The more light the body is subject to, was the conclusion, the more rapidly it stops its production of melatonin thus releasing the body to develop sexually. I summarized these references in The Red Lamp of Incest in 1980. The relevance to the study of incest is obvious in that the drop in age of menarche thrusts families into a condition that is radically different from the one in which we evolved: our "environment of evolutionary adpatedness" where girls matured in their late teens even though they were usually married earlier.

Could this be the simple clue? Our young girls are bombarded with ever more intense and intrusive light, including lately that from TV and fluorescent lighting, and their daylight hours are literally "unnaturally" lengthened almost to breaking point. The pineal gland, geared to the natural light cycle, responds to the light invasion with a drop in melatonin production and the gates to maturity are opened at an earlier and earlier age. We have reached a low of 7 and the ever-eager merchandisers are promoting padded bras and lipstick for seven-year olds. How low can it go? We don't know as we don't know so much about the effects of civilization on the savage mind and body, but we seem to be reaching a limit.

Why does this not affect boys? It does somewhat - their age at puberty has indeed dropped but much, much less. Their massive growth spurt that Tanner discovered, derived as it is from the independent source of testosterone, remains unaffected by lengthening and intensity of light. (Girls get some more testosterone but significantly less than boys.) The boys grow faster and bigger than they did, but they mature sexually at a similar rate to their ancestors. This then becomes one more example of how we intrude into the evolved order of things with consequences we did not intend but which can become a disaster. However, there are websites (from one of which I took the picture) that will help you get in touch with God through pineal gland exercises. Do not abandon hope.

This all of course affects our concern with the "problem" of teenage pregnancy, but that is for another time. Read on.