Sexual Selection in Man: I. Touch. II. Smell. III. Hearing. IV. Vision
If we analyze the stimuli to tumescence as they proceed from a person of the opposite sex we find that they are all appeals which must come through the channels of four senses: touch, smell, hearing, and, above all, vision. When a man or a woman experiences sexual love for one particular person from among the multitude by which he or she is surrounded, this is due to the influences of a group of stimuli coming through the channels of one or more of these senses. There has been a sexual selection conditioned by sensory stimuli. This is true even of the finer and more spiritual influences that proceed from one person to another, although, in order to grasp the phenomena adequately, it is best to insist on the more fundamental and less complex forms which they assume. In this sense sexual selection is no longer a hypothesis concerning the truth of which it is possible to dispute; it is a self-evident fact. The difficulty is not as to its existence, but as to the methods by which it may be most precisely measured. It is fundamentally a psychological process, and should be approached from the psychological side.