Commitment to Relationships and Preferences for Feminity and Apparent Health in Faces are Strongest on Days of the Mentrual Cycle when Progesterone Level is High. - Jones,B.C.; Little,A.C.; Boothroyd,L.G.; Debruine,L.M.; Feinberg,D.R.; Law Smith,M.J.; Cornwell,R.E.; Moore,F.R.; Perrett,D.I. (Horm Behav, 2005)