Bost doctors accept that the age of onset of puberty is dropping steadily among children in the developed world.
Studies have showed this to be the case for girls, and new research carried out by Herman-Giddens, and published by the American Academy of Pediatrics, has found the same for boys. The age of onset of biological adulthood continues to plunge. Consider the stats provided by German researchers.
They found that in 1860, the average age of the onset of puberty in girls was 16.6 years. In 1920, it was 14.6; in 1950, 13.1; 1980, 12.5; and in 2010, it had dropped to 10.5. Similar sets of figures have been reported for boys, albeit with a delay of around a year.
What factors lie behind this trend? Answers are still debated, although most scientists and health experts believe that the initial decline in the age in puberty was linked to general improvements in health in the west that began in the late 19th century. The trouble is that this drop, which was expected to stop, has simply continued at the same rate: a decline in four to five months in age of onset for each passing decade.
The relentless slide has begun to worry the doctors who have proposed a host of causes to explain it.
Increasing obesity is often quoted. In the young it is thought to increase blood levels of oestrogens that promote breast development and early studies seemed to confirm this by linking puberty to higher body mass index. However, a Danish study released last year in the journal Paediatrics found puberty occurring earlier in children regardless of body mass index at age seven.
Other factors that may be involved include a diet that is increasingly high in sugar and fat and declining physical activity.
Chemicals in diet
The cause could also be environmental, say other researchers - in particular, exposure to endocrine disrupters, chemicals in the environment that act on hormones.
Widespread industrial and pharmaceutical pollutants have already been shown to harm the normal sexual development of fish and animals. They may also contribute to earlier or disrupted puberty in children.