Some have argued in the past that the development of the chin could be a purely random example of 'genetic drift', with no evolutionary purpose whatsoever.
However, the new research - published in the Journal of Human Evolution - says that because the evolution of the chin happened 77 times faster than the average genetic change, it is highly unlikely to have been random.
Dr Pampush calculated that the chin began to emerge some time between 6million and 200,000 years ago, with the most likely estimate being around 2million years ago.
This would coincide with the enormous leap forward in human intelligence, which led to breakthroughs including the invention of cooking.
The evolution of the chin came about as a result of humans' teeth and jaws shrinking, because they no longer needed to chew through raw meat and plants, Dr Pampush told the Independent on Sunday.
'My guess is that it happened around two million years ago when there was a jump in brain size,' he said. 'We had a soft diet, and we no longer needed big teeth.
'I'm guessing the changes which ultimately lead to the chin are directly related to cooking, and indirectly related to larger brains and bodies.'
Because the chin is a by-product of an evolutionary change, rather than being selected for directly, it is what scientists call a 'spandrel'.
Dr Pampush's new theory goes against previous suggestions that the chin was an example of sexual selection, with prominent chins marking out men who are likely to make good mates.
The fact that both men and women have chins means the sexual selection theory is unlikely, because such developments usually apply only to one of the sexes, not both.
Another theory put forward in the past claimed that the chin was a way to balance out the stress put on the jaw by the action of chewing, but Dr Pampush also cast doubt on that idea.
- Daily Mail
