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>Women's attraction varies with their menstrual cycles. For example, heterosexual women prefer more masculine-looking men, and more symmetrical men, when they are most fertile (Roney and Simmons, 2008; Thornhill and Gangestad, 1999). Women’s attitudes toward their own partners can also change across their cycles: Women who perceive their partners as more sexually attractive rate them more positively when the women are fertile, while women who perceive their partners as less sexually attractive rate them more negatively when fertile (Larson et al., 2013). Further, when women are in the fertile portion of their menstrual cycles (and their estrogen levels are high), they are more interested in sex with men other than their primary partners. However, when they are in the less fertile portion of their cycles (and their progesterone levels are high), they are more interested in sex with their primary partners (Grebe et al., 2016).
>Why would women's attraction to men change over time? Women should be attracted to men with good genes, but men who are more attractive may be less inclined to invest in or care for future offspring (Gangestad and Simpson, 2000). Researchers suggest that women may pursue a mixed mating strategy, mating with a kind and supportive long-term mate to help care for and provide for offspring while pursuing men with good genes for short term sexual relationships (Cousins, 2015).
TL;DR: females are pretty based
