Having a bad day at work? Take it on the chin. And here's why you have one (a chin, not a bad day).

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.