Baboon sexual swellings and male response: A possible operational mammalian supernormal stimulus and response interaction

Experimental work using coagulated masturbatory seminal emissions from nine adult male chacma baboons (Papio ursinus)as a dependent variable revealed that males show a greater sexual arousal response to female conspecifics exhibiting exaggerated perineal swellings. The menstrual cycles of the “superswollen” females did not differ in length or patterning from the controls. Since additional experimental work, including behavioral observations on females with normal and supersized swellings, failed to reveal differences in female proceptivity, the male’s increased arousal response appears dependent upon the perineal size per se.The males’ responses suggest that the supersized swellings may be an example of an operational visual supernormal stimulus and response interaction.