There is a famous phrase that says, "Beauty is in the eye of the beholder." If the beholder is a fertile female you may want to go for the less attractive look. According to new research attractive women should be careful when asking for a pay raise if their boss is a female. Women who are at their peak fertility are more competitive towards their equally attractive counterparts.

Researchers from Wellesley College conducted a study, which women completed with an on-screen virtual partner. The test included an economic game where women had to make an offer to the partner. She was instructed to offer an amount and keep the rest for herself. Following the test, women were instructed to rate the partner's attractiveness on the scale from one to 10.

The study revealed during a woman's most fertile stage, she is more likely to make smaller offers to other attractive female employees. On average, women during peaks of fertility offered nearly 25 percent less to their attractive counterparts. Conversely, during a woman's low fertility stage, researchers observed women would offer 20 percent more.

Researchers theorize this thought process stems from the hunter-gatherer days. In hunting and gathering societies, women would deny other women, who might compete for good male stock, resources.

"What we found supports the idea that, among women, competitiveness during periods of high fertility is linked to the withholding of resources from potential rivals," said Dr Margery Lucas, professor of psychology told The Independent. "Resource competition is important because women need to acquire products - clothing, makeup, accessories, and so on - to enhance their attractiveness. By offering less to attractive women and keeping more for themselves, fertile women can help to enhance their own appearance and weaken a competitor's ability to do the same."

Lucas recommends when negotiating a pay increase one should be aware of a woman's menstrual cycle and level of attractiveness.