A new study in the journal Animal Cognition says that the grass-in-ear fad has become a new cultural aspect for some chimpanzees, in much the same way that fads like Rubik’s Cubes or gladiator sandals at one point were all the rage for us humans.
“Our observation is quite unique in the sense that nothing seems to be communicated by it,” said Edwin van Leeuwen, an author of the study and a primate expert at the Max Planck Institute in Nijmegen, Netherlands.
To confirm that chimpanzees were sticking grass in their ears due to culture and not by fluke, the research team observed for one year four chimp troops at Chimfunshi Wildlife Orphanage in Zambia. They found that only one of the four troops stuck grass in their ears, even though all the observed chimpanzees lived in the same area.
The team couldn’t find any genetic or ecological factors, and concluded that the behaviour was learned through natural transmission.
The behaviour first came up in 2010 when Julie, a chimpanzee who was a role model for 11 other chimps, was spotted with the piece of grass coming out of her ear. Seven of those chimps ended up adopting the behaviour, and kept doing it even after Julie died.
The team reported that the chimps that adopted the behaviour would often stick grass in their ears before grooming or playing, and the grass remained in their ears for long periods of time before they finally removed them.
