Much like the origin of language, the origin of music has been a topic of great speculation and debate for centuries. Charles Darwin thought that “some early progenitor of man” started singing crudely, “as do some of the gibbon-apes at the present day”, “during the courtship of the sexes”. In other words, Darwin thought songs and musical expressions appeared and then proliferated because our ancestors noticed music could get them laid.

Others suggest that music is merely an adaptation from an ancestral trait, such as territorial calls and signals. A new study adds weight to this line of thinking. Researchers at the University of Warwick, the University of Torino, and the Max Planck Institute for Psycholinguistics, found that Madagascan lemurs — small black-and-white primates — make rhythmic “honks” during their alarm calls. It sounds a bit like a car horn.

These lemurs can also sing on a beat — a very rare trait in the animal kingdom with only humans, songbirds, and gibbons in this exclusive club. In 2016, researchers found that lemurs co-sing certain parts of their song with other group members, effectively forming a choir.

These primates got rhythm

The finding that these “singing lemurs” also produce rhythmic calls suggests that the ability to produce and perceive rhythm is more ancient than previously thought. The discovery also provides an evolutionary pathway that may explain the origin of music, showing “the foundational elements of human music can be traced back to early primate communication systems”.

“It (the sense of rhythm) is deeply rooted in our evolutionary journey and may have evolved for other reasons than just music,” said Dr. Chiara De Gregorio, from Warwick’s Department of Psychology.

De Gregorio and colleagues analyzed recorded calls produced by 51 indri lemurs (Indri indri) in five rainforests across Madagascar. Over 15 years the researchers gathered this singing data. And, using acoustic analysis software, they examined the rhythmic patterns.

The lemurs sang when they needed to locate other family groups or send alarm calls when spotting a predator. They used rhythmic honks when spotting a land predator and roars for eagles and other birds.

Overall, the researchers identified three distinct types of rhythm: 1:1 (or isochrony) where the notes are evenly spaced; 1:2 where the gap between one note is twice as long as the previous one; and 2:1 where the second note is twice as long as the first.

Singing and survival on a timer

Rhythmic isochrony, a beat similar to the ticking of a clock, is rare in human speech but common in music. Its presence in indri vocalizations suggests it might be an ancient feature shared by the common ancestors of both humans and primates. The feature might have been naturally selected for its role in social communication, particularly in territorial advertisement.

Humans and indris last shared a common ancestor some 77 million years ago. So, the researchers speculate that the ability must have evolved independently.

“This discovery positions indris as animals with the highest number of vocal rhythms shared with the human musical repertoire — surpassing songbirds and other mammals,” said De Gregorio.

Unfortunately, indri lemurs are critically endangered due to habitat destruction, primarily driven by deforestation for agriculture and logging. There are fewer than 10,000 individuals left in the wild. Conservation efforts are underway to protect their dwindling populations. The focus is on habitat preservation and local community involvement to ensure these unique lemurs continue to sing through the forests of Madagascar.

“We are very worried. If people want to see [this species], they should go to Madagascar now, because we cannot assure that in 50 years’ time, they will still be there,” said De Gregorio.

The findings appeared in the Annals of the New York Academy of Sciences.