Puberty

Puberty is the stage of the human lifespan in which a child develops secondary sex characteristics (for example deeper voice in boys, and development of breasts in girls) as his or her hormonal balance shifts strongly towards an adult state. This is triggered by the pituitary gland, which secretes a surge of hormones into the blood stream and begins the rapid maturation of the gonads: the girl's ovaries and the boy's testicles. Girls tend to enter puberty approximately a year earlier than boys.

The onset of puberty in girls especially appears to be related to body fat percentage. In most Western countries, the average age of menarche fell, in a secular trend, over the last century. There are numerous theories as to why this is including improved nutrition, increased caloric intake, increased artificial hormones present in meats, other preservatives and chemicals used in the modern processing of foods, and decreased melatonin levels due to the increased exposure to and prevalence of (artificial) lights such as are emitted from televisions, nightlights, and computer monitors.

Some theorists believe that analysis of data shows the age of onset of menarche to correlate to whether a girl lives with her natural father, a stepfather, or no father at all. Yet others propose a climatological connection and attribute the decreased average age of menarche in part to climate change or global warming. The debates regarding both of these theories are politically charged.

Historically this stage of development began much later, sometime between the ages of fourteen and eighteen, which allowed the child to mentally and emotionally mature more and brought them closer to the age of consent before reaching this physically and emotionally challenging developmental stage.