Darwin proposed two primary means by which sexual selection could operate. The first is intrasexual competition—competition between members of one sex, the outcomes of which contri... Darwin proposed two primary means by which sexual selection could operate. The first is intrasexual competition—competition between members of one sex, the outcomes of which contributed to mating access to the other sex. The prototype of intrasexual competition is two stags locking horns in combat. The victor gains sexual access to a female either directly or through controlling territory or other resources desired by the female. The loser typically fails to mate. Whatever qualities lead to success in the same-sex contests, such as greater size, strength, or athletic ability, will be passed on to the next generation because of the mating success of the victors. Qualities linked with losing fail to get passed on. So, evolution—change over time—can occur simply as a consequence of intrasexual competition. The second means by which sexual selection could operate is intersexual selection, or preferential mate choice. If members of one sex have some consensus about the qualities that are desired in members of the opposite sex, then individuals of the opposite sex who possess those qualities will be preferentially chosen as mates. Those who lack the desired qualities mate less often or fail to attract mates entirely. In this case, evolutionary change occurs simply because the qualities that are desired in a mate increase in frequency with the passing of each generation. If females prefer to mate with males who give them gifts of food, for example, then males with qualities that lead to success in acquiring food gifts will increase in frequency over time. Darwin called the process of intersexual selection 'female choice' because he observed that throughout the animal world, females of many species seemed to be more discriminating or choosy than males about whom they mated with. Read more