Giant lemurs are the first mammals (besides us) to use musical rhythm

Mammals make all kinds of sounds, but their cries rarely sound like music. The guilty? A lack of rhythm – the temporal sequence that organizes sounds, and the pauses between them, into a repeatable pattern. Humans were previously the only known mammals to use rhythm to create music. To find out how we might have acquired this ear for timing, scientists are exploring the musical abilities of other species.

That’s why a team of researchers recently ventured into the jungles of Madagascar, armed with microphones to record the remarkable cries of the indri lemur (Indri-indri). Indris look like lanky black and white teddy bears with piercing green eyes. They often perch high in the rainforest canopy, where, despite being the largest lemur species, they can be difficult to spot. Animals are easy to hear, however; their bellowing cries are recognizable from over a mile away. In addition to their prodigious hits, the indris boast a varied vocal repertoire, including a high-pitched “song” resembling a moan that echoes in the forest.

The Indri live in family groups and their distinctive songs help the groups communicate with each other. Like a family orchestra, the adults perform painfully sounding duets before the offspring join in a cacophonous chorus. These songs are “hauntingly beautiful,” says Andrea Ravignani, a biomusicologist at the Max Planck Institute for Psycholinguistics in Nijmegen, the Netherlands.

Indri’s songs may seem chaotic at first, but University of Turin biologist Chiara De Gregorio says they start to sound less, so the more you hear them. “When you get used to it, you can really recognize a pattern in these songs,” she says. “When they start a sentence, you know what to expect, note after note.” In a new study published in current biology, De Gregorio, Ravignani and their colleagues analyzed recordings of 636 individual indri songs collected from 20 different family groups to determine whether these noisy lemurs in fact possess rhythm.

Two-month-old Indri. Credit: Bernard Castelein/Nature Picture Library/Alamy Stock Photo

Because rhythm is all about timing, the team dissected each recording into its basic elements to measure the duration of the notes and the pauses between them. The researchers compared the lengths of the intervals between each sound and found that songs often broke down into rhythmic ratios of 1:1 (when the intervals between sounds are the same length, such as singing with a metronome) or 1:2 ( when the first interval is half as long as the second). Both are common in human music.

The researchers say their study shows that indris use these patterns to structure their songs, making this the first confirmed case of a non-human mammal possessing a human-like categorical rhythm.* Their findings apply to all indris that they recorded; women and men sang to different rhythms, but both employed the same rhythmic patterns. Indris has also shown the ability to maintain a steady beat by decreasing the tempo of their songs – a process known in classical music as ritardando.

Although human indris and composers may use similar structures, each likely developed musical abilities separately. It’s been 77.5 million years since the common ancestor of humans and indris existed, a chasm of evolutionary time that makes it unlikely that rhythm was an ancestral trait. Ravignani instead suggests that similar social pressures turned indris and humans into singers at different times – an example of convergent evolution. The exact benefits this ability confers on indris are still unknown, but the authors speculate that organizing songs into repeatable patterns could make it easier for young lemurs to learn, or help indri families coordinate quickly when they need help. defend their territory or gather.

Elizabeth St. Clair, a biological anthropologist at Johns Hopkins University who studies the evolution of the primate vocal tract, says she was surprised by the rhythmic similarities between the indri and human songs. “It appears to be an individual characteristic of indris that is not seen in many other mammals or even birds,” says St. Clair, who was not involved in the new study. She suspects that gibbons, small Southeast Asian monkeys known to coordinate their calls, may also use rhythm to structure their songs.

Dissection of indri songs indicates that these animals share an underlying sense of rhythm with humans, but this raises more questions about how indris communicate. “After our recent discovery, I think these giant lemurs are hiding [even] more common traits with humans than previously thought,” says De Gregorio. She wonders how an indri’s song develops as the primate matures and what specific purposes can be served by it. communicate through repetitive sounds.

Unfortunately, the time to answer questions like these may be lacking. Deforestation and hunting have devastated indri populations (as well as gibbons); some experts believe that as low as 1,000 indris remain in the wild and all signs indicate that this number is decreasing. Madagascar’s forests are expected to decline by up to 93 percent by 2070.

Researchers hope conservation efforts will help indris survive long into the future. As scientists try to figure out why primates started using music, hearing the songs of wild indris will be crucial. “Their communication system is an indirect window into their mind,” explains Ravignani. “They have a lot of secrets hidden in their heads, and by watching their sound production, we can uncover them.”

Editor’s Note (9/12/21): A version of this article with the title “Lemur Rhythm” has been adapted for inclusion in the January 2022 issue of American Scientist. This text reflects that version, with the addition of some material that has been abridged for printing.

*Editor’s Note (04/01/22): This sentence was edited after publication to clarify the type of categorical rhythm exhibited by indris.