Scientists may have solved the mystery of why humans are the only animals to have chins - and it all comes down to the invention of cooking.
A number of different explanations have been put forward for the apparently useless bony projection, including the idea that it helps humans attract a mate.
Now, a new research at the University of Florida suggests the chin began to emerge as a consequence of major changes six million years earlier.
The arrival of cooking and softer food meant humans no longer needed big teeth and powerful jaws, and over the next two million years both got smaller and the chin was born, 'The Independent' reported.
Researchers led by anthropologist Dr James Pampush collected chin data from over 100 primate species and compared it with historical data.
Computer modelling traced the shifting orientation of the front of the jaw and the rate at which the chin evolved.
The study suggests the chin is what is known as a spandrel - an evolutionary by-product of another event. In this case, the event could well be the advent of cooking.
"It (the event) had to have occurred between six million to 200,000 years ago - six million years ago is the timing of the split between humans and chimpanzees," said Pampush.
"My guess is that it happened around two million years ago when there was a jump in brain size. We had a soft diet, and we no longer needed big teeth.
"Around two million years ago there were a lot of changes to the 'human-like' animals. Homo erectus had a larger body size, much larger brains, was probably cooking and there's a good chance they were using clothing," said Pampush.
The changes which ultimately lead to the chin are directly related to cooking, and indirectly related to larger brains and bodies, Pampush added.
The study was published in the Journal of Human Evolution.
