A “singing” endangered animal reveals the evolutionary origins of music

When Chiara de Gregorio thinks of rhythm, two things come to mind: the mega-hit “We Will Rock You” by the British band Queen and endangered lemurs.

Specifically, she’s thinking of the Indri indri, an endangered lemur residing on the island nation of Madagascar. De Gregorio’s team researched musical rhythm in the Indri indri, publishing her team’s findings in the journal Current Biology on Monday.

“The two rhythmic categories we found [for the Indri indri], are exactly the same of the intro of ‘We Will Rock You,’ by the famous band Queen,” De Gregorio, lead author on the study and researcher in the University of Turin’s Department of Life Sciences and Systems Biology, tells Inverse.

The simple, well-timed beats in “We Will Rock You” made the rock banger an iconic hit, but they also speak to the universal language that humans share across cultures and languages: rhythm.

According to Gregorio’s recent study, the Indri indri is the only other creature in the animal kingdom — so far — that can replicate Queen’s iconic beat. Her findings speak to a shared rhythmic language between humans and this rare creature, suggesting humans aren’t the only mammals who enjoy a well-timed beat.

How they made the discovery — An endangered animal on the island nation of Madagascar might seem like an odd subject for a musical experiment. But the researchers decided to focus on the Indri indri as their subject for one specific reason: they’re one of the few primates in the world known for their singing abilities.

These endangered lemurs don’t just sing at random. Researchers have observed that their songs contain specific phrases — a good indication of categorical rhythms, when intervals between notes occur not uniformly, but in deliberate ways.

“Rather than defining music itself, categorical rhythms may inform the temporal organization of an acoustic signal,” De Gregorio says.

Think of the uniform intervals between the beats of a ticking clock. We probably wouldn’t categorize these uniform beats alone as music. On the other hand, we recognize the specifically timed or categorical intervals between the beats in “We Will Rock You” as music.

“Since indris’ songs are composed of notes that are organized in phrases, they were very good candidates to understand if indris would share the same categorical rhythms that are typical of human music,” De Gregorio says.

Researchers recorded the indris’ singing in the wild to scientifically confirm their hunch, then measured the intervals between the lemur’s musical notes using mathematical ratios.

“We then calculated the ratios between two subsequent notes by dividing each onset for its duration plus the duration of the following one,” De Gregorio adds.

Musical notes that have intervals of the same length would have a ratio of 1:1 — a more uniform interval similar to a ticking clock or metronome. But if a note has half the interval of a previous note, the ratio would be 1:2 — a smaller, less uniform ratio.

As the researchers write, these ratios indicate “aspects of human musicality rare in other species.” Therefore, finding these two musical ratios in a lemur’s singing would be a total gamechanger.

What they found — Through their research, scientists confirmed the Indri indri is the first non-human mammal known to display universal rhythm.

The researchers found the intervals between lemurs’ musical notes weren’t uniformly distributed, similar to the “discretely-sampled note durations found in human music,” according to the study.

The scientists also found two rhythmic categories in the lemur’s singing, matching the iconic beats of “We Will Rock You” by Queen.

“The fact that we have found two different categories is something a bit unexpected, as it indicates that indris’ songs are even more special than previously thought!” De Gregorio says.

Why it matters — Despite linguistic and cultural differences, humans across the globe speak in one shared language: musical rhythm.

We can all recognize a good beat when we hear one, and we’ll often clap along, unprompted, even when we’re hearing a song for the first time. Humans are naturally attuned to picking up and promoting rhythms, allowing us to create music.

“Categorical rhythms have been found across human music in different cultures, so they are a musical universal,” De Gregorio says.

Until now, humans thought we were alone in our ability to construct a categorical rhythm with unique musical patterns. With these findings in hand, researchers are one step closer to unlocking the evolutionary origins of rhythm itself.

“Finding in indris [a] musical universal may indicate that human music is not truly novel, but its intrinsic musical properties are more deeply rooted in the primate lineage than previously thought,” De Gregorio says.

What’s next — The research team’s findings are exciting, but they come at a critical time for lemurs. The IUCN Red List notes the Indri indri is critically endangered — the last step before a species faces extinction. Hunting, mining, and climate change all threaten the creature’s habitat.

“It is really sad to think how endangered these special primates are: at the moment, every attempt to build captive populations have failed and their habitat is vanishing very quickly,” De Gregorio says. “Once the forest is gone, they are gone too.”

De Gregorio hopes her work can extend beyond the academic realm to help save the Indri indri from extinction.

If the general public becomes aware of the animal’s rhythmic abilities, it could spur conservation efforts, similar to how whale songs propelled the “Save the Whales” movement in the 1970s.

“We hope that this exciting finding can also bring attention to indris’ critical situation,” De Gregorio.

Abstract: What are the origins of musical rhythm? One approach to the biology and evolution of music consists in finding common musical traits across species. These similarities allow biomusicologists to infer when and how musical traits appeared in our species. A parallel approach to the biology and evolution of music focuses on finding statistical universals in human music. These include rhythmic features that appear above chance across musical cultures. One such universal is the production of categorical rhythms, defined as those where temporal intervals between note onsets are distributed categorically rather than uniformly. Prominent rhythm categories include those with intervals related by small integer ratios, such as 1:1 (isochrony) and 1:2, which translates as some notes being twice as long as their adjacent ones. In humans, universals are often defined in relation to the beat, a top-down cognitive process of inferring a temporal regularity from a complex musical scene. Without assuming the presence of the beat in other animals, one can still investigate its downstream products, namely rhythmic categories with small integer ratios detected in recorded signals. Here we combine the comparative and statistical universals approaches, testing the hypothesis that rhythmic categories and small integer ratios should appear in species showing coordinated group singing. We find that a lemur species displays, in its coordinated songs, the isochronous and 1:2 rhythm categories seen in human music, showing that such categories are not, among mammals, unique to humans.