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The mystery of why humans are the only animals to have chins may have been solved by scientists who suggest that it is linked to the invention of cooking.

A number of different explanations have been put forward for the apparently useless appendage, including the idea that it helps humans attract a mate.

But new research pours cold water on that theory - pointing instead to the way the jaw evolved and shrank to deal with the fact that cooking was making food softer.

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Evolution: The human chin, as sported prominently here by six different celebrities, is apparently connected to the development of cooking; scroll down to find out the owners of these chins

A paper from the University of Florida is the latest attempt to explain exactly why humans - unlike all other primates - have chins.

Author James Pampush points out that the fact that apes and monkeys do not have chins proves that they must have evolved after the ancestors of man split off from other branches of the primate family.

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.

1) Football manager and commentator Jimmy Hill is known for his large chin; 2) Reese Witherspoon is another star with the prominent facial feature

Witherspoon is another star with the prominent facial feature

3) Bruce Forsyth would not be as recognisable without his large chin; 4) The Thinker by Rodin depicts a man resting his head on his chin

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.'

5) Buzz Lightyear is a caricature of the square-jawed action hero; 6) Meg Ryan is known for her large chin

Contrast: Chimpanzees and monkeys do not have chins, meaning that they must have evolved after humans split off from other primates in the evolutionary tree

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.