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sexual selection; mate choice Neuroendocrinology Letters 2001; 22:309–321 pii: NEL220501R01 Copyright © Neuroendocrinology Letters 2001 Abstract The effect of sensory input on hormones is essential to any explanation of mammalian behavior, including aspects of physical attraction. The chemical signals we send have direct and developmental effects on hormone levels in other people. Since we don‘t know either if, or how, visual cues might have direct and developmental effects on hormone levels in other people, the biological basis for the development of visually perceived human physi-cal attraction is currently somewhat questionable. In contrast, the biologi-cal basis for the development of physical attraction based on chemical sig-nals is well detailed. 310 The human sense of smell The importance of the human sense of smell has been largely underestimated. Many people believ