Like cat videos, it's pretty easy to stumble over dancing animal videos online. Are these animals really hearing the music and keeping a beat, or are they merely moving around at someone else's behest?
The question has turned into a burgeoning scientific field—one that looks at everything from boy-band-loving cockatoos to head-bobbing sea lions—with implications for how and why music evolved in people.
Every human culture through time that we know of has evolved some kind of music, says Aniruddh Patel, a cognitive neuroscientist at Tufts University in Medford, Massachusetts, who spoke at a presentation during the ongoing American Association for the Advancement of Science (AAAS) conference.
But how deeply rooted our penchant for music is still eludes researchers. It could be that music is simply an extension of our ability to imitate sounds, while others including Charles Darwin have proposed that a sense of rhythm is common in all animals as a consequence of similar wiring in our nervous systems. (See "Why Did Humans Invent Music?")
It wasn't until 2009 when researchers got their first glimpse into the ability to keep a beat in animals. Patel received a link to a video of Snowball the cockatoo dancing to "Everybody" by the Backstreet Boys.
The researcher contacted Snowball's owner to see if he could run the bird through tests designed to see if the cockatoo was simply following a human dancer off-camera, or if the bird was truly keeping a beat.
It turned out that Snowball could adjust his dance moves when Patel slowed the song down or sped it up. That flexibility is key to determining whether animals can follow a melody like people can, Patel explains.
Since then, scientists have demonstrated that a similar, if less flexible, ability exists in bonobos and chimpanzees. And a captive sea lion at the University of California, Santa Cruz has become quite proficient at bobbing her head in time to "Boogie Wonderland."
National Geographic caught up with Patel at AAAS to talk about the perception of rhythm and music in people and in animals.
How long have people have been looking at the ability of other animals to follow a beat?
In biology, there's been a long interest in synchrony among certain species. It's well known for example that there are certain fireflies that will flash synchronously. And this has been studied since the 70s.
But in terms of animals' sensitivity to musical beats and being able to synchronize to an auditory beat in the way that we do, which is very flexible—being able to slow down and speed up and extracting that beat from music—that's very recent.
The first paper was the paper I published in 2009 [on Snowball]. It's the earliest example of another species having that capacity.
What other animals can do this?
We're talking about sensitivity to an auditory beat and moving to the beat synchronously, but also being able to do it at a broad range of different tempi like a human can. So far only parrots and a sea lion—Peter Cook showed that a sea lion could do this.
There's also video evidence that some elephants can do it. But that's still a little uncertain, I would say. But the parrots are pretty solid and the sea lion work is pretty solid.
What about nonhuman primates?
There is one published study by a researcher in Japan, Yuko Hattori, who should be here speaking today, showing that chimpanzees can synchronize to a metronome at one tempo, near their spontaneous tempo—[which] is the tempo that they like to tap anyway. But they don't show this flexibility where if you slow it down or speed it up, they spontaneously match it.
But it's a young field. Maybe with a little bit more training and experience, [the chimpanzees] will show it.
When do we gain the ability to synchronize to a beat?
We know kids around four or five can do it. Younger kids can do it too, but usually only at one tempo close to their preferred tempo. And then as you grow older you broaden the tempi at which you can do this. But I would say it emerges between three and five.
You mention that there are different parts of our brain involved in our ability to move to a beat. Which ones are they?
So when we just perceive a beat—this is just sensing a beat in music, even when we're not moving—there seems to be a widespread network involving auditory regions [and] the motor planning regions of the brain. Regions that are normally involved in planning movements, which is interesting because you're not moving or even intending to move. But those regions are playing some sort of role in analyzing the rhythmic structure.
Deep brain structures like the basal ganglia, the cerebellum—they're known to be important for timing. Parts of the parietal cortex, which are thought to be important in integrating different brain regions and mapping between them.
And so you see this broad network, which suggests that it's not a simple function of some little brain area. It actually requires a lot of coordination, which is one reason why it might not be that easy for many other species and takes a while to develop [in people] and is related to other aspects of cognition and so forth.
Has anyone looked at what areas of the brain are involved in animals?
Hugo Merchant, the neurobiologist from Mexico is here. He has been studying tapping to a beat in monkeys. He's actually measuring from parts of their brains while they do this. So he is the person to ask about what brain regions [are involved]—in monkeys, anyway. But they don't seem to quite do it the way we do it.
So following a rhythm has been seen in parrots, a sea lion, maybe in elephants, bonobos, and chimps. What does that mean in terms of its adaptive value, or importance in evolution?
The theory that I propose is that somehow, it's a consequence of being able to imitate sound. We can imitate complex sounds unlike any other primate. And that means you have to have special connections between your hearing centers and your movement centers in your brain. I felt that laid the groundwork for this other ability, which is also a connection between hearing and movement.
If that's true, then in a sense, this ability [to follow a rhythm] was a byproduct in evolution. And that's why I tested the theory with the parrot and why I'm so interested in the monkey work.
So far the theory's held up except for the sea lions, which are not known to be vocal learners. But, on the other hand, they're not known not to be either, so it's a little bit up in the air with them.
It may be a byproduct of something else that we do, or, if Darwin's theory is right, it's just a deep aspect of brain function that music builds on.
In terms of its adaptive value, people have speculated that it played some role in social bonding in humans. Moving in synchrony makes people feel connected socially and emotionally.
Is this kind of behavior seen in animals that aren't social?
Well, the insects. Fireflies, they're not really social. The flash, they'll be near each other when they're doing this behavior, but they don't live socially and cooperate when they're foraging or anything like that.
What animals would you like to see tested next?
Horses. Absolutely. I just published a paper with a method for testing horses and whether or not they synchronize to the beat of music. Because, they are definitely not vocally flexible, they're not related to any vocally flexible animals.
One of the ambiguities of the sea lion work is they're related to seals that we know are vocally flexible, whereas horses don't have any vocally flexible near-relatives.
And people will occasionally tell me [horses] spontaneously entrain to the beat of music, and that would really be a conclusive refutation of my hypothesis. So, I would love for somebody to test horses.
This Q&A has been edited and condensed.
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