IF you think it's obvious why some men don't fancy women with large chins, think again.

According to scientists, it may not be simply because they find them unattractive. They say, a prominent chin can be a telltale sign that a woman will be unfaithful, reported The Daily Mail.

Their conclusion comes from research conducted by a team of psychologists. They took a group of young women and questioned them on their sexual histories and fantasies.

The women were then rated by a group of men on their desirability as a future partner.

Rule of jaw: The dainty-chinned Joanne Woodward and husband Paul Newman remained happily married for 50 years.

The men were not told about the sex questionnaires. However, the results showed that women with larger chins were more sexually active than those with softer chins - and that men found these women unattractive.

The scientists, from four universities in North America, concluded that men will shun women with such masculine features when looking for a long-term partner because there is an instinctive fear of being cuckolded.

A large chin is often the product of a high level of the male growth hormone testosterone, which is present in all women in various amounts.

But a high level of the hormone increases sexual assertiveness in a woman, a tendency more attributed to males.

This article was first published in The New Paper on Feb 2, 2009.