Sexual Dimorphism in Facial Shapes and Their Discrimination in Japanese Monkeys
(Macaca fuscata)Reiko Koba, Akihiro Izumi, Katsuki Nakamura ニホンザルを対象に、同種対個体の顔写真による性弁別を検討した。まず、顔の形や、目や鼻などのサイズを計測し、性差を調べた。その結果、顎や鼻はメスよりもオスの方が長く、上顎や顔上部の輪郭に性差がみられた。次に、オペラント条件付けを２頭のニホンザルを対象におこなったところ、顔写真から性弁別が可能であることが示された。さらに、画像計測から得られた顔の形態的特徴が、性弁別の手掛りとなっているか、モーフィング刺激を用いて検討した。オス顔をメスの形態へと変形させたところ、オス反応率が下がり、顔の形態情報が性弁別の手掛りとして用いられている可能性が示唆された Journal of Comparative Psychology, 123: 326-333, 2009 The authors examined the ability of Japanese monkeys
(Macaca fuscata) to discriminate between sexes based on facial features. The shape and position of facial features (facial morphology) were measured to quantify the differences between sexes. The distance between the chin and nose was longer in males than females, and the outline of the face around the upper jaw and upper face differed between sexes. Using operant conditioning, 2 monkeys succeeded in discriminating sex based on facial pictures. Furthermore, they successfully generalized the discrimination to novel pictures of faces. Tests with morphed pictures of faces revealed that the monkeys used facial morphology to discriminate between males and females. Our results suggest that Japanese monkeys have sexual dimorphism in facial shape and they can use the morphological differences to discriminate conspecific sex. NOV/25/2009
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