Graham said that while she and her colleagues are always careful to keep their distance from the wild primates they are studying, sometimes their inquisitive subjects break that intended barrier.
She recalls a young bonobo named Natsuko who would teasingly run up to the researchers, shake branches, and then run away. Bonobos appear to do this amongst themselves to get attention.
"'Object shake' is a somewhat ambiguous gesture, so I don't know what she wanted from us, but it definitely wasn't for us to ignore her," Graham said.
Robert Seyfarth is one of the world's leading experts on primate communication and other primate social behaviors. He and his wife Dorothy Cheney have conducted decades of fieldwork on various non-human primates. The pair were mentored by Robert Hinde (1923–2016), the noted animal behaviorist who supervised Jane Goodall's dissertation on the behavior of chimpanzees in the mid-1960s.
Seyfarth told Seeker that he was not surprised by the discovery that bonobos and chimps share many gestures, and that physically similar gestures in the two species have roughly the same meaning.
"Chimps and bonobos, after all, share many things: They live in similar habitats and have similar anatomy, social organizations, and social relationships," Seyfarth explained.
RELATED: Chimps and Six-Year-Olds Want to Mete Out Punishment — Even If It Comes at a Cost
He said that the similarities could have evolved in a few different ways. The gestures might have evolved before the shared lineage of chimps and bonobos separated, or they could have converged after separation, or a bit of both.
"Given the results of this paper, it would be interesting to compare the gestures of gorillas with those of chimps and bonobos," he said, explaining that gorillas are not as closely related to chimps and bonobos as the latter two primates are to each other.
Byrne indicated that this additional research was on the horizon.
He said, "We have yet to compare the meanings of gestures of the chimpanzee and bonobo with those of the gorilla, but that species too has a repertoire of gestures that are very similar in physical form, and I would predict that they too will prove to be closely similar in meaning."
Gorilla DNA suggests that human primate forbearers and gorillas last shared a common ancestor around 10 million years ago. If gorillas do share certain gestures with humans, bonobos, and chimps, then those gestures could have been present in the human primate lineage for millions of years.
The researchers hint that the likely inherited longstanding skill helps to explain why people may understand non-human primate gestures so well.
"We have just finished an online experiment with over 15,000 participants assessing whether humans can understand chimpanzee and bonobo gestures," Graham said. "We showed people videos of chimpanzee and bonobo gestures and asked what they think the gestures mean. We're analyzing the results now and it looks really exciting, but that's about all we can say for the moment."