I can't even count the number of times people have repeated to me the myth that eating beef raised with hormones for added meat has contributed to modern children hitting puberty younger than children did in the past. (Here's an earlier post on a related topic: "Marriage and Pregnancy").
The truth of the matter is a bit more mundane. There are several factors that lead to earlier puberty among modern first-world humans, and the major ones are:
1. More food. There's plenty of food to go around, and studies show over and over that heavier kids reach puberty sooner. Why? The several-years-long process requires around 400 extra calories per day for boys and around 300 for girls, and that's quite a lot of energy.
2. Better nutrition. Related to number 1, the body requires a sufficient supply of various vitamins and minerals, and American kids today eat better than kids ever have before.
(Incidentally, 1 and 2 also explain why people are taller now than they were in the past.)
3. Television. Television? Maybe. More specifically, kids who watch more television tend to be heavier and have less exposure to natural light.
Children who watch a lot of television produce less melatonin, new research suggests - the "sleep hormone" has been linked to timing of puberty.The article also notes that other studies have shown correlation between watching TV and earlier sexual experiences.
Scientists at the University of Florence in Italy found that when youngsters were deprived of their TV sets, computers and video games, their melatonin production increased by an average 30 per cent.
“Girls are reaching puberty much earlier than in the 1950s. One reason is due to their average increase in weight; but another may be due to reduced levels of melatonin,” suggests Roberto Salti, who led the study. “Animal studies have shown that low melatonin levels have an important role in promoting an early onset of puberty.”
Commenting on the research, Alessandra Graziottin, director of the Centre for Gynaecology and Medical Sexology in Milan, said the results were very interesting and plausible. She told La Repubblica newspaper: “US studies have shown that the greater the exposure to television, the earlier the age of sexual experience, including teenage pregnancies.”Perhaps the effect isn't merely the result of the sexually-charged programs on TV, but is also related to our biochemistry.