The year of the monkey continues with news that is far less terrifying (and perhaps more relatable) than hearing about primates learning how to fish or stealing buses or other assorted evolutionary milestones. Scientists at the Leiden University in the Netherlands have discovered chimpanzees really like butts, and they cannot lie. Chimpanzees are so butt-focused, in fact, that they can recognize a set of chimp buttocks in the same way a human can remember familiar faces as long as the picture isn’t flipped upside down (the inversion effect).
They published their research in PLOS One with the title Getting to the bottom of face processing. (Nice.)
While the importance of buttocks in chimpanzee society is well-known — the anogenital region of chimpanzee buttocks swells and reddens around the time of ovulation, for example — it wasn’t known if they processed characteristics of individual buttocks in the same way as humans process faces. The so-called inversion effect means that humans process information about faces in a totally different way to how they process information about other objects.
The researchers found chimpanzees do remember butts the way humans remember faces, and they have even more difficulty recognizing inverted images. The researchers speculated the human ability to recognize faces may have evolved from an earlier reliance on looking at butts for “socio-sexual signalling” (as if we don’t still look at butts). I don’t know about their speculation. Seems like they kind of pulled it out of… a hat. Surely there could be other reasons chimps are so good at remembering butts. Maybe because they’re living their best life. Have the scientists considered that?