omen tend to choose genetically superior men for their short-term sexual relationships and are most likely to cheat on their long-term partner when they are at their most fertile period, according to a study.

Czech researchers, whose study was quoted by Nature magazine, found that the smell of a socially dominant male is most exciting to women in stable relationships, especially on days when they are ovulating.

Jan Havlmcek, of Charles University in Prague, and his colleagues asked 48 men to complete a questionnaire, rating statements in order to score the volunteers' social dominance. The researchers also asked them to wear cotton pads under their arms to collect sweat.

A group of 65 women then smelled the pads and rated the sexiness and masculinity of the scent. Women in the middle week of their menstrual cycle, the point at which fertility is at its peak, tended to prefer the smell of the men who scored highest on the dominance quiz, the study revealed.

This preference was not shown by women at other points in their cycle, the researchers say. The results support a theory of mixed mating strategies, which argues that women should want different things from different men at different times.

Females are expected to pair up with the males most likely to invest in parental care, but any affair is likely to be conducted with successful males who, although they may not be good dads, provide good genes.

"Other studies have shown that women are more likely to get involved in extra-pair affairs during their fertile period," Havlmcek says. "We suppose that in such cases more socially dominant males would be preferred."