We like to think of ourselves as being somewhat higher than the apes. While chimpanzees might be incredibly intelligent, they still kill and devour infants, chow down on ear wax, and pick through their poop to eat any undigested seeds that their body might have missed. On the surface, it seems there is little that can gross out a chimpanzee.
Well, it turns out that, broadly speaking, we’re a lot more similar when it comes to disgust then you might assume.
It is generally thought that the disgust most people show towards things like bodily fluids is an adaptive system that evolved in order to protect us against contamination from diseases and parasites that might be festering in bodily products. So strong is this feeling that it is almost a universal human response, and yet whether or not other primates show this had not actually been tested before.
“If chimpanzees and other primates can discern contamination risk via different cues, individuals with higher sensitivities to feces and other bodily fluids may be less infected, which could have important health benefits,” explained Cecile Sarabian, who led the research published in Royal Society Open Science. “Moreover, such results may have implications for animal welfare and management.”
It would stand to reason that despite some questionable behavior chimpanzees, with their impressive cognitive know-how, might have evolved such disgust reactions. To test it out, the researchers from the Primate Research Institute at Kyoto University used a mixture of visual, touch and smell to see if it altered whether chimps were likely to eat a bit of food.
The chimps were more likely to delay nibbling on food that had been placed on a lump of fake poop when compared to a control, and generally avoided the smell of poop, blood, and semen. But none of these were enough to stop the ape from eating entirely.
When it came to touch, however, the reactions were much stronger. The researchers placed the food in boxes, and while in one there was just a piece of rope in the other they put the food on some soft and moist dough. As the chimps reached in, they reacted exactly how you would expect anyone to when touching a soft, moist object, and recoiled almost immediately.
“While anyone watching the reactions of these chimpanzees in the tactile experiments can empathize with them, it's premature to say that they feel the same as we might in that situation” noted Andrew MacIntosh, senior author of the study.
What it does hint at, however, is the origin of disgust in humans, which could help us understand where this protective reaction comes from. The next step is to explore disgust further in other primates and in other animals in general.