Evolution of the nose and nasal skeleton in primates

One traditional diagnostic feature of the Order Primates is a decreased emphasis on olfaction.1,2 Some authors attribute this feature only to tarsiers and anthropoids, either through convergence or as a common feature of haplorhines.^2-4 Other authors de-emphasize olfaction relative to vision,^5-7 which does not necessarily denote olfactory reduction per se. There are lengthy roots to this discussion. The importance of the sense of smell to at least some primates, humans in particular, has long been viewed as secondary to the importance of visual, auditory, and tactile senses. Smell, or olfaction, is viewed as the primitive special sense, the stimuli perceived in an unconscious manner, submerged relative to higher neural functions,¹ and a sense that has been increasingly reduced during the course of primate evolution.^1-8 Anatomical structures related to olfaction differ profoundly in proportions and complexity between higher taxonomic groups of primates (Haplorhini, Strepsirrhini). These anatomical differences are beyond dispute (Box 1). However, the relationship between the anatomical differences and primate sensory abilities, and hence the validity of using them to group primates into "microsmatic" or "macrosmatic" categories,^9,10 is less clear when we examine the physiological and genetic data on primate olfaction.