Research into one of the handful of primate groups known to “sing” has revealed that Indri indri lemurs have rhythm equivalent to our own. The discovery of musicality in these lemurs represents an exciting entry into the musical tree of life, enabling scientists to better map out how rhythm first evolved, and through which shared ancestors it spread. While such musical skill is well documented in humans and birds, this is the first evidence of categorical rhythm in a non-human mammal.
Categorical rhythm can be used to describe a song whose notes or beats exhibit consistent durations. It’s essentially what makes music so identifiable from other sounds and is why you can still recognize a song even if it’s being played at double speed.
To find out if this kind of rhythm was present in a group of singing lemurs, the study, published in the journal Current Biology, recorded the songs of 20 indri lemur groups over the course of 12 years. In total, their sample contained 39 animals, who would get together and sing in duets and choruses. Previous research has found young indri lemurs will purposefully sing out of sync to get their parents' attention, sneaky.
Analyses of the recordings showed the lemurs did indeed have a rhythmic universal with several trends becoming apparent throughout their singing. There were sex differences between singing style, as while males and females stuck to the same rhythm, their tempos differed. Songs exhibited something known in human music as “ritardando” whereby a song gradually slows down, and even fit the rhythmic category of arguably one of the most famous musical introductions in humans history.
“In human music rhythm plays a very important role, and intervals between the beginning of a note and that of the following one usually have a simple relationship,” said first author Chiara de Gregorio to IFLScience. “For example, two subsequent intervals may have the same duration, or maybe the second is twice the first one.
“These two cases correspond to two rhythmic categories, and we can find them, for example, in the intro of “We Will Rock You”, the famous song by Queen. Guess what? Those are exactly the same two rhythmic categories we discovered in the indris’ songs. This is the first evidence of the presence of a typical trait of human music in another mammal.”
Their musical talents raise questions as to how this talent makes them a better fit for their environment, and where a common ancestor (if one exists) sits in the evolutionary timeline to explain the various groups that have independently evolved the skill. According to the paper, humans’ and indris’ last common ancestor lived 77.5 million years ago, indicating that music’s roots among mammals could well run very, very deep.
“Music and rhythm are two very important aspects in our daily life,” said de Gregorio. “Still, the reason why we enjoy so much music and dancing is highly debated. Finding in indris musical universals 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.”