THE SPERM WHALE'S NOSE: SEXUAL SELECTION ON A GRAND SCALE?1

Authors


  • 1

    I would like to dedicate this paper to my major professor, Kenneth S. Norris and acknowledge the years of stalwart support and sage advice he provided. The astute reader will recognize that many of the ideas presented here have been espoused by him for decades (although some never found their way into the literature) or are logical extensions of his “natural intuition.” His original work with George Harvey on the anatomy of the sperm whale's nose laid the stepping stones in a pathway that I have followed with my research for the past fifteen years. I can only accept modest credit for plodding along a path so well forged. Whenever I lost my way, it was often Ken who shone the light ahead and gently nudged me in the right direction. I owe him an enormous measure of gratitude for sculpting the path, furnishing a map, lighting a beacon, and reminding me to enjoy nature's splendor along the way.

Abstract

The world's largest nose belongs to the sperm whale, yet its functional significance remains equivocal. In order to help shed light on its function, the head of a postmortem neonate sperm whale was subjected to CT scanning. Geometric comparisons between homologous cephalic structures in sperm whales and dolphins (normalized for body size) show extreme hypertrophy and size sexual dimorphism in the sperm whale's lipid spermaceti organ. Anatomic geometry, energetics, and behavior suggest that this immense nasal apparatus is a bioacoustical machine. Sexual selection via an acoustic display is suggested as an explanation for the size and continuous (physiologically isolated) energy investment in the construction and maintenance of the male's spermaceti organ.

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