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Singing isn’t the weirdest thing the human animal does, but it’s pretty weird. Music isn’t just art, it’s a form of communication. Songs have an ability to communicate thoughts and feelings in a way that simple words can’t accomplish. Stranger still, certain elements of music appear to be universal across geographies and cultures, which suggests there’s something neurologically innate happening. Music is something we evolved to enjoy and collectively understand.
Precisely how structured musical ability evolved in humans is a question of some debate. One way to explore the question involves looking at other animals to see if they exhibit similar behaviors. Scientists supposed that musical structures like categorical rhythm might exist among species who display coordinated group singing, like some primates.
Chiara De Gregorio from the Department of Life Sciences and Systems Biology at the University of Turin in Italy, along with colleagues, spent 12 years observing a species of lemur (indri indri) in their natural habitats in Madagascar. Using microphones, they recorded solo and group vocalizations of the large black and white primates in search of universal musical structures. And they found them. Their findings were published in the journal Current Biology.
“Many animals have rhythm, a pattern of intervals between the beginning of a vocalization and that of the following one,” De Gregorio told SYFY WIRE. “For example, drumming behavior, as the generation of rhythmic sounds using hands or feet, is quite common in chimpanzees, bonobos, and gorillas. But categorical rhythms have never been really investigated in non-human animals, except for only two species of birds: they share with humans only isochrony, that is when onsets are evenly spaced. Instead, indris share with human music two different rhythms, which makes their songs quite complex and articulated.”
Common rhythms found in human music include 1:1, like the consistent tapping of a metronome, and 1:2, wherein some notes are twice as long as others. To date, indris are the only other known mammal which utilizes categorical rhythms in their music. Even those primates closely related to us, like chimpanzees, don’t display this behavior.
That they utilize complex musical structures seems to be confirmed, whether or not their songs are enjoyable is another question altogether. You can decide for yourself in the video below (but be warned: at least one cat had an absolute fit when she heard it; headphones and low volume are recommended).
That a species so distantly separated from us on the evolutionary tree should share musical structures with us could suggest that the behavior evolved independently. Alternatively, it might suggest that these structures were in place during the time of our last common ancestor with indris, and were subsequently lost by some members of our family.
“Our results can be an important piece of evidence towards our understanding of the origins of our rhythmic abilities, our love for dancing, and our passion for music. Despite being so important in our daily life, the ultimate reason for the existence of rhythm and music is still highly debated. Finding in indris musical universals may indicate that human music is not truly novel but its intrinsic musical properties were already in place more than 70 million years ago,” De Gregoria said.
It's also possible that categorical rhythmic structures do exist in other primates, and we just haven’t discovered that yet. The discovery of categorical rhythms in songbirds was only confirmed in 2020, and its existence in indris comes hot on its heels. There’s every possibility that musical universals are present in all sorts of animals and they’re out there waiting for us to hear their songs.
“I think that other primates’ songs can be perfect candidates for this kind of investigation,” De Gregoria said. “Gibbons and titi monkeys might possess rhythmic categories, as their displays are similar in terms of function and structure to the indris.”
The team would like to continue studying indris to learn more about their musical abilities. Specifically, they hope to discover if the rhythmic structures are present from birth or a learned behavior. But the opportunity to complete those studies is threatened, as the indri is critically endangered. Estimates of the remaining populations in the wild vary from 1,000 to 10,000, and conservation efforts are challenging.
“At the moment, every attempt to build captive populations have failed and their habitat is vanishing at a very fast rate,” De Gregorio said. “They still have so much to teach us, and our research group is working very hard also for their conservation. We hope this exciting finding can also bring attention to their critical situation.”
That’s a message worth playing on repeat. If we’re not careful, the incredible songs of the indris might be replaced with the haunting sound of silence.