Chimps Recognize Butts That Are Upside-Down, Too

A new study builds on prize-winning do-chimps-recognize-buttocks research, adding an upside-down appraisal:

Getting to the Bottom of Face Processing. Species-Specific Inversion Effects for Faces and Behinds in Humans and Chimpanzees (Pan Troglodytes),” Mariska E. Kret and Masaki Tomonaga, PLOS ONE, November 30, 2016. The authors, at Leiden University, the Netherlands, and Kyoto University, Japan, build on work, by other researchers, that won an Ig Nobel Anatomy Prize:


“In four different delayed matching-to-sample tasks with upright and inverted body parts, we show that humans demonstrate a face, but not a behind inversion effect and that chimpanzees show a behind, but no clear face inversion effect. The findings suggest an evolutionary shift in socio-sexual signalling function from behinds to faces, two hairless, symmetrical and attractive body parts.”


Leiden University issued a press release that gives further colorful details.

The 2012 Ig Nobel Prize for anatomy was awarded to Frans de Waal and Jennifer Pokorny, for discovering that chimpanzees can identify other chimpanzees individually from seeing photographs of their rear ends. They describe that research, in the study “Faces and Behinds: Chimpanzee Sex Perception“, Frans B.M. de Waal and Jennifer J. Pokorny, Advanced Science Letters, vol. 1, 2008, pp. 99–103.

Frans de Waal was pleased to see his Ig Nobel-winning research confirmed by this new study, he told the Dutch newspaper de Volkskrant: ‘Ik ben blij dat deze nieuwe studie dat bevestigt‘.

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