Last week's Nature has a series of articles on adolescence, that ghastly period between carefree and careworn that used to coincide with the teenage thirteen-nineteen years but now starts earlier and ends later. I was chatting to a colleague at work a couple of years ago: her son, aged 24, a student, living at home; had borrowed The Mammy's car, driven it and some pals to Kerry and back and returned it with an empty gas-tank. It was only the empty gas-tank that really riled her up; the other dependencies seemed quite natural. By contrast, my aged father-in-law Pat the Salt ran away to sea a few weeks after he turned 14, leaving a note for his mother at the shipping office. 1939 was not the safest year to join the merchant marine but it was quite exciting, and occasionally very wet, for a young chap. A lot more exciting that Grand Theft Auto, that's for sure.
The conservative position is that bringing forward the start of puberty (by a whole year in Denmark between 1991 and 2016) is driven by calories. In the 1980s, Rose Frisch floated the association between fat and fertility as causative. Her hypothesis was that girls were only ready for reproductive activity if they had the spare calories to support a 40 week drain on resources during pregnancy. The developing body assessed 'spare calories' in presence of sufficient sub-cutaneous fat: if there was enough, then menarche was triggered. Frisch's work has been extended and critiqued since then, but it is epidemiologically true that fat girls start their periods earlier than their skinnier class-mates. It's not the same for boys and may even by opposite. But then, a young chap's contribution to the next generation need only be five minutes and a tea-spoonful. A different take on the causes of the earlier and earlier start of puberty is to lay part of the blame on BPA - the plasticiser and steroid hormone analogue that is omnipresent in babies bottles and elsewhere in the commercial food delivery world.
In the aftermath of WWII, there was concern that British children were not getting enough calories and that this might affect how they grew. If the growth of children was stunted, they wouldn't be much use in the factories of manufacturing economy. A paediatrician James Tanner was tasked with measuring children in a longitudinal study as they grew up. That was useful and one of the outputs of the study were Tanner Charts of normal development. Doctors and parents thereafter could see whether a child was in the normal range of height and weight for their age. There is a bit of skepticism about with the kids who were measured were 'normal' themselves because most were recruits from the National Children's home in Harpenden and may have been calorie-handicapped quite apart from what other traumas separated them from their parents. But while the team was measuring height and weight, they also took the opportunity to measure testis size, sub-cutaneous fat, breast development. They also had regular X-rays to check for bone development (and TB) and dental exams to check for caries. It also seemed important to take photographs of their scrawny and stark naked frames - front and back. Those pictures are in an archive somewhere. None of this would pass modern standards to informed consent, so one could argue that this fundamental data of the speed and order in which things happened during puberty was providentially gathered in a nick of time.
The Nature article makes an attempt to tease out whether adolescent behaviour is triggered by the hormones, or whether the 'child' steps up to the plate of autonomy and responsibility because they are treated like an initiate. Me, I think its a raw deal altogether to wrench an innocent 9 year old [or younger] girl away from playing with dolls and making cup-cakes to start on the whole spots and tufts and boobs gig. But heck, what do I know?