"It is certain that very much of what is best in religion, art, and life," remark Stanley Hall and Allin, "owes its charm to the progressively-widening irradiation of sexual feeling. Perhaps the reluctance of the female first long-circuited the exquisite sensations connected with sexual organs and acts to the antics of animal and human courtship, while restraint had the physiological function of developing the colors, plumes, excessive activity, and exuberant life of the pairing season. To keep certain parts of the body covered, irradiated the sense of beauty to eyes, hair, face, complexion, dress, form, etc., while many savage dances, costumes and postures are irradiations of the sexual act. Thus reticence, concealment, and restraint are among the prime conditions of religion and human culture." (Stanley Hall and Allin, "The Psychology of Tickling," _American Journal of Psychology_, 1897, p. 31.) Groos attributes the deepening of the conjugal relation among birds to the circumstance that the male seeks to overcome the reticence of the female by the display of his charms and abilities. "And in the human world," he continues, "it is the same; without the modest reserve of the woman that must, in most cases, be overcome by lovable qualities, the sexual relationship would with difficulty find a singer who would extol in love the highest movements of the human soul." (Groos, _Spiele der Menschen_, p. 341.)