Our ancestors had it easy – they never had to deal with adolescents. Grumpy, awkward teenagers are a recent invention in evolution, according to scientists who have been studying fossil teeth fragments of Homo erectus, who lived 1.5 million years ago.
In those times, children matured straight into adults without passing through the difficult phase typified by "Kevin", as portrayed by the comedian Harry Enfield.
However, adolescence is reckoned to be a crucial event in the development of intelligence in modern humans, or Homo sapiens.
"While humans take a good 18 to 20 years to grow up, other primate species like chimpanzees and gorillas take just 11 or 12 years," said Professor Christopher Dean, of the evolutionary anatomy unit at University College London, who led the study. "One of the things that sets modern humans apart from the living great apes is our long period of growth and development."
The research, which was done on parts of a young male Homo erectus skeleton found in Kenya, is reported today in the science journal Nature.
The scientists note that it is surprising, because Homo erectus was the first human ancestor to show numerous modern human characteristics; besides standing upright, erectus had similar body proportions, weight and small teeth and jaws.
Professor Dean said: "It seems likely that the first permanent molar tooth, which erupts at around six years in modern humans and at about 3.5 years in apes, erupted between four and 4.5 years in Homo erectus.
"Previously, most people accepted this boy was close to 11 or 12 years of age, but now it seems more likely he was closer to eight years of age, which is a surprise because he was already 5ft 3ins tall."
The earliest dental evidence for a modern human growth period comes from a Neanderthal living about 120,000 years ago.
Professor Dean said: "It seems our prolonged period of growth and development may be a more recent evolutionary acquisition that arose in step with our comparatively recent development of a larger, modern, human-sized brain."