A new study says sexual attraction and jealousy might be traced to monthly changes in a woman’s cycle of fertility.

The report, published in the journal Hormones and Behavior, suggests that women who describe their partners as unattractive are more inclined to lust for other men in the days just before ovulation, when they are most likely to conceive, the Albuquerque (N.M.) Journal reported.

University of New Mexico psychologist Steven Gangestad said less-attractive partners are more likely to show jealous behavior at those times of peak fertility.

The study didn’t attempt to learn whether women are inclined to act on any lustful impulses, the newspaper said.

As women approach maximum fertility, some biological impulse appears to rouse interest in men with robust, masculine attributes, said Gangestad, who co-authored the study with Matie Haselton, a psychologist at the University of California, Los Angeles.

Women picked guys based on factors that suggested a healthy, more masculine guy likely to sire robust children, he said.

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