HORMONAL ONSET OF PUBERTY. The biological clock that regulates the timing of puberty still has not been discovered. It is something of a mystery that the age of puberty has been decreasing by an average of four months every ten years for the last century and a half. No explanation, including improved nutrition, or change in the dark/light ratio after candles and firelight were replaced by kerosene lamps, gas, and electricity amounts to more than a speculative hypothesis.

Though it does not always hold up in cases of extreme precocity or delay in the onset of puberty, there is a correlation between body size and the ratio of fat to lean body weight and the onset of puberty. The correlation itself does not clarify which is cause and which effect. In cases of child abuse dwarfism (also known as reversible hyposomatotropic dwarfism, and as psychosocial dwarfism), not only growth hormone but also, at the age of puberty, gonadotropic secretion from the pituitary may be suppressed. In one extreme case, a boy aged sixteen had the stature and nonpubertal development of an eight-year-old. Rescued from the home of abuse, he grew rapidly and became pubertal in less than a year.

The most likely localization of the biological clock of puberty is in the central nervous system. There is some clinical and experimental evidence to implicate the brain’s pineal gland, especially in cases of early puberty occurring in conjunction with a pineal tumor. Todays evidence, however, points primarily to the hypothalamus and its nearby connections in the limbic system of the brain. The hypothalamus secretes its own neurohormones or neurotransmitters that signal the endocrine system via the pituitary gland. The pituitary, in turn, signals the gonads to secrete their own sex hormones.