Complex sentence: The ovulatory shift hypothesis proposes that motivation and desire to mate should increase during the fertile window in order to maximize reproductive success, and that cycle shifts may have evolved to lead females to seek and attract the best possible mate.
Split into simpler sentences: The ovulatory shift hypothesis proposes that motivation and desire to mate should increase during the fertile window in order to maximize reproductive success. The theory also proposes that cycle shifts may have evolved to lead females to seek and attract the best possible mate.