London, Oct 14 (IANS) Women bosses become "ruthless" and far more competitive at the peak of their fertility during a month, and hence were less likely to give attractive women a pay rise, says a study by US experts.
This attitude dates back to the hunter-gatherer days when a woman had to look after herself and withhold as much as possible from rivals in order to attract men, the Daily Mail reported.
Women bosses at their fertility peak could offer up to 25 percent less pay to their female counterparts, according to psychologists at Wellesley College in the US.
Psychology professor Margery Lucas said women need to consider their timing as well as how attractive their bosses are before negotiating any deal.
During the study, women had to offer a certain salary to an on-screen virtual partner, and keep the rest for herself.
At the end of the test, they rated the partner's attractiveness on a 10-point scale, the daily said.
Scientists said the results showed that on average women in the fertile stage of the month offered 25 percent less to the most attractive women compared to the least attractive women.
Women at the low-fertility stage were far more generous, offering 20 percent more to the prettiest women than they did to the least good looking.
The researchers said it suggests that women at the low-fertility stage are less threatened by beautiful female co-workers.
"Among women, competitiveness during periods of high fertility is linked to the withholding of resources from potential rivals. Resource competition is important because women need to acquire products - clothing, makeup, accessories, and so on - to enhance their attractiveness," the lead expert said.
"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," she said.
"Women today should be aware that in, for example, salary negotiations, menstrual cycle phase, along with the attractiveness and sex of the negotiation partner, could interact in complex and potentially costly ways," she was quoted as saying.