A Sense of Rhythm: Birds, Lemurs, Whales and Us

Candice Gaukel Andrews November 23, 2021 0
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Researchers recently set out to look for musical abilities in lemurs, which will allow them to build an “evolutionary tree” of musical traits and understand how rhythm originated and evolved in humans.

You probably do it in the car. Some of us do it in the shower. And when no one else is home, a good number of us might even do it in front of the mirror with an imaginary microphone.

Then, there are those who do it in the rain (I’m looking at you, Gene Kelly.)

We sing. The ability to carry a tune isn’t even all that important because the very act of singing—even off-key—makes us feel good. Singing has the power to alter our moods and conjure up memories. It provides an emotional release; a way to express our thoughts and feelings.

But is our human aptitude for music and rhythms unique in nature? Do other animals have senses of rhythm like ours? Of course, one of the most striking similarities between humans and birds is the ability to make song. And we know that dolphins and whales can create complex musical phrases; but other than those exceptions, the capacity appears to be rare in the natural world.

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For us, singing provides an emotional release; we sing to express our thoughts and feelings. Like the adage says, “Where words fail, music speaks.”

Now, however, researchers report that they may have found a sense of rhythm in another primate—and that our notions of what a “song” is may not be applicable when we look at other animal cultures.

Indri intervals

Unlike a painting or a piece of sculpture, which are compositions in space, a musical work is dependent upon time. In other words, rhythm is music’s pattern in time. Whatever other elements a given piece of music may have (such as pitch or timbre), rhythm is the one indispensable component in all music. Rhythm can exist without melody—as in the drumbeats of some indigenous music—but melody cannot exist without rhythm.

Evolutionary theory maintains that physical characteristics develop because they’re needed; because they bring their owner an advantage. But what need was there for the human throat to have evolved a larynx that can produce such musically accurate sounds, over such an astonishing range? Whatever that need, it must have existed a very long time ago to allow such a complex anatomical device to develop. It may even have existed among our far distant, humanoid ancestors before our species, Homo sapiens, appeared on Earth.

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Birds and humans share the ability to make songs. But that skill seems to be rare in the natural world.

So, do other, present-day primates exhibit senses of rhythm? An international team of researchers endeavored to find out.

For their study, the scientists chose one of the few “singing” primates, the critically endangered lemur Indri indri. Visiting the rain forests of Madagascar to collaborate with a local primate study group, the researchers investigated whether indri songs have categorial rhythm, a “rhythmic universal” found across human musical cultures. Rhythm is categorical when intervals between sounds have the same duration (1:1 rhythm) or doubled duration (1:2 rhythm). This type of rhythm makes a song easily recognizable, even if it is sung at different speeds.

Rain forest ritardando

Over a period of 12 years, the investigators recorded songs from 20 indri groups (39 animals), living in their natural habitats. Indri family group members tend to sing together, in harmonized choruses and duets. The research team found that indri songs had the classic rhythmic categories (both 1:1 and 1:2), as well as the typical ritardando (a gradual slackening in tempo) found in several human musical traditions. Male and female lemur songs had a different tempo but showed the same rhythm.

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Well over half of Madagascar’s species are found in the rain forests, which lie on the island’s east coast.

According to the study’s authors, this is the first evidence of a rhythmic universal in a nonhuman mammal. But why should another primate produce categorical, music-like rhythms? The ability probably evolved independently among singing species, as the last common ancestor between humans and indris lived 77.5 million years ago. One theory is that rhythm may make it easier to produce and process songs, or even to learn them.

Cetacean changes

While whales have been identified as one of those other, rare mammals that sing, it could be that their songs defy the human definition of a song.

Many scientists frame whale songs as similar to bird vocalizations, designed for attracting potential mates or warnings to competitors. But for the past several years, researcher Eduardo Mercado III, at the University at Buffalo in New York, has been proposing a radically different story about whale songs. In his latest study, published in the journal Animal Cognition in August 2021, he argues for a departure from treating whale songs as the underwater analog to birdsong.

Scientists deploy a hydrophone in the North Atlantic that will record sounds emitted by endangered whales and other species. ©Dave Mellinger, Oregon State University, flickr

His findings reveal the changing nature of the units within whale songs and the way they further morph through the years. These changes represent a vocal flexibility that demonstrates the inadequacy of using human labels—such as cries, chirps and moans—for a species with the capacity for much more sophisticated sound production. What the whale singers are doing seems to be much more dynamic, both within songs and across years, making it a matter of switching from thinking about whale songs as musical notes to something more free-form, such as dancing.

Current hypotheses assume whales combine sounds (units) into patterns (phrases) to construct the songs that reveal their fitness to possible mates. From this perspective, single units are like individual quills in a peacock’s tail, each functionally equal and useful only as a collective. But the units are not functionally equal, according to Dr. Mercado’s paper. The unit morphing produces some units that are much less detectable than others, a finding that challenges previous conclusions regarding fitness in favor of the songs instead signifying locations and movements, with each change making relevant units easier to hear across long distances.

There are clear differences in the units when listening to whale songs from different years, says Mercado. They’re so different that it’s like switching from one musical genre to another. In any given year, the whales use an altogether different set of sounds.

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Previously, it was assumed that whales combine sounds into patterns to create songs that advertise their breeding fitness. From this perspective, single units are like individual quills in a peacock’s tail, each functionally equal and useful only as a collective.

Could these changes be random? It’s not likely. Dr. Mercado relied on a method that collected detailed measures of variations in units produced by whale singers, and then he compared those measures to characteristics produced in different years. This approach emphasized variability in vocal behavior rather than summaries of unit types.

Dr. Mercado likened the changes to people with no preparation shifting languages several times over a 10-year span, and everyone continuing to understand everyone else despite it. So, if the whales are changing sounds, how are other whales making sense of them?

It seems that the modifications adhere to a clear set of rules, such as maintaining pitch ranges even when the sounds appear subjectively to be varying quite a bit. The morphing of these units might contribute to the overall function of the songs, possibly by increasing the number of positions from which listening whales can reliably detect, localize and track the tunes.

At least one researcher wants us to think of whale songs not as musical notes but like something more free-form, such as dancing. ©Navin75, flickr

That flexibility demonstrates the shortcomings inherent in computational or subjective methods for sorting units into discrete categories that don’t capture nuances of vocalizations. Shifts in pitch, for example, might force an incorrect recategorization of units. We might think we’re hearing something different, but the whale might be saying nothing has changed.

Humans, Mercado concludes, are not the gold standard for distinguishing sounds, and we must acknowledge and respect that when conducting research.

Songs for sensibilities

We have a lot to learn about the “songs” of other animals. In recognition of that fact, the authors of the lemur rhythm study encourage other researchers to gather data on indris and other endangered species “before it is too late to witness their breathtaking singing displays.”

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The lemur-study scientists encourage other researchers to gather data on indris and other endangered species with rhythm to learn more about the musical propensities we share before it’s too late.

Primarily, humans sing because something inside us needs to express something beyond words.

I think that may be the major reason the “others” among us do, too.

Here’s to finding your true places and natural habitats,

Candy

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