(A) the fact that there is a supply-demand gap, fewer women available for casual sex than men, giving them a bargaining position....women can AFFORD to be more selective about casual sex partner attractiveness.
OR
(B) regardless of supply demand gap, when it comes sex alone, women are NATURALLY more selective about who she wants to have sex with.
OR
(B) regardless of supply demand gap, when it comes sex alone, women are NATURALLY more selective about who she wants to have sex with.