Our distant primate relative, the Indri indri, is a critically endangered species of lemur found only in Madagascar. These black-and-white primates are the weight of a small dog and look like a cross between a cat and a koala. And they sound — depending on whom you ask — like the shriek of a balloon quickly releasing air.
Andrea Ravignani, a cognitive biologist at the Max Planck Institute for Psycholinguistics in the Netherlands, disagrees with the balloon part.
“Every scientific discipline has its concept of beauty, but I think their vocalizations are beautiful,” he said. “And also quite complex.”
Dr. Ravignani and his colleagues investigated that complexity and found that, although the last common ancestor between humans and indris lived over 77 million years ago, we’re more similar than you may think, at least when it comes to singing. They published their findings on Monday in Current Biology.
Singing and rhythm in other animals have intrigued scientists for decades, in part because they can provide us insight into our own evolution.
“We can infer things about when, and how, we acquired certain key aspects of musicality, like our ability to move to a beat or coordinate our pitch with others’,” said Aniruddh Patel, who was not involved in the study but whose research at Tufts University focuses on music cognition in humans and other species, like Snowball the cockatoo. You may have seen Snowball bopping to the beat of “Everybody (Backstreet’s Back)” by the Backstreet Boys in a late-2000s YouTube video.
Following Snowball, there were rhythm findings in other organisms — like parakeets and a California sea lion named Ronan. But the rhythmic capabilities of our closer relatives, especially as they related to singing, remained more mysterious.
“Only a few primate species sing, so they are precious resources in our search for the evolutionary origins of human musicality,” Dr. Patel said.
Researchers from Madagascar and the University of Turin recorded songs from 20 indri groups (39 animals total) for over 12 years and searched those songs for rhythmic features found in human music. They discovered two examples of humanlike rhythm in the lemur songs: a 1:1 rhythm, in which intervals between two sounds have the same duration, and a 1:2 rhythm, in which the second interval is twice as long as the first one. They also noticed a gradual decrease in tempo, a common feature in human music called a “ritardando.”
This is the first time these categorical rhythms have been identified in a nonhuman mammal. The findings suggest that the lemurs have a sense of the beat, the repeating pulse that allows us — OK, some of us — to move in time with music.
“When you’re listening to a musical piece and dancing to it, you’re basically processing this very complex stream of sounds, extracting some regularities from it, and then predicting what’s coming next,” Dr. Ravignani said. “If an indri had some sort of metronome in its head going ‘tac, tac, tac,’ then they would likely produce what we see. It’s so close to human music — it’s quite astonishing.”
Whether this musical overlap between humans and indris is a case of common ancestry or convergent evolution — where our rhythmic abilities evolved independently — remains unclear. The researchers suspect it’s a combination of the two.
“It is easy to suggest that rhythmic categories may have followed the same evolutionary trajectory in singing species such as songbirds, indris and humans,” said Chiara De Gregorio, a researcher at the University of Turin and study co-author. “But we can’t rule out that human music is not truly novel but possesses intrinsic musical properties that are more deeply rooted in the primate lineage than previously thought.”
Exploring our commonalities with indris is helping to demystify the evolutionary origins of human music, but it is also bringing much-needed attention to these lemurs who are of incredible cultural importance to the Malagasy people.