April 4, 2013 | 2
Ronan is the name of a the California sea lion (Zalophus californianus) who can bob her head in time to music. She apparently dances to Boogie Wonderland, and the Backstreet Boys song Everybody. She can move her head in rhythm with the beats of a metronome. She’s in the news this week because a new study from the University of California, Santa Cruz, where she lives after being rescued by the Long Marine Lab, announced that she displays evidence of “rhythmic entrainment,” or the ability to sync the movements of one’s body with an external source of sound or music. I’ve written about this before:
Many species like the bird of paradise have various sorts of mating rituals, which could be described as “dances” by analogy. But dancing means something more specific: the “rhythmic entrainment to music.” Dancing requires that an individual moves his or her arms, legs, and body in sync with a musical beat. All human cultures ever encountered can do this, and until recently we thought this talent or ability was unique to our species. Until, that is, a celebrity parrot named Snowball knocked us off our place of perceived prominence.
This could be really big news. Why?
“…People thought that vocal mimicry might actually be a necessary precondition for rhythmic ability,” the researcher explains in the video abstract above. “But our findings with Ronan, who as a sea lion is not a vocal mimic, challenge that theory.”
Indeed, the prevailing theory is that it isn’t just humans that can dance, but any species capable of vocal learning, which also includes elephants, some bats, songbirds, parrots, hummingbirds, cetaceans like dolphins and whales, and seals. It was Aniruddh D. Patel who forumulated this hypothesis in 2006, writing:
…the foregoing observations can be condensed into a specific and testable hypothesis, namely that having the neural circuitry for complex vocal learning is a necessary prerequisite for the ability to synchronize with an auditory beat. This “vocal learning and rhythmic synchronization hypothesis” predicts that attempts to teach nonhuman primates to synchronize to a beat will not be successful.
Subsequent attempts to look for rhythmic entrainment in rhesus monkeys have indeed not been successful. It was thought that this was because humans are the only primates who have vocal learning. Chimpanzees don’t, bonobos don’t, and neither do gorillas, orangutans, or any of the many monkey species.
In general, sea lions are not considered to be vocal learners. However, operant conditioning experiments with California sea lions conducted in the 1960s showed that sea lions are able to learn and modify vocal responses to external stimuli, and produce or inhibit certain calls in a fairly flexible way. Most vocal calls are thought to be innate and reflexive, not subject to modification by learning nor to subjective control.
“Virtually all marine mammals can be very easily trained to vocalize on command, in stark contrast to any primate or most terrestrial mammals,” Tecumseh Fitch, an expert on the evolution of language and bioacoustics, told me by email. And that is “probably about the need for breath control during diving.”
It’s worth pointing out that part of the confusion may stem from sea lions’ slippery cousins, the seals. “True” or “earless” seals are members of the family Phocidae which includes the famous harbor seal Hoover. They are vocal learners. But another group of pinnipeds is the family Otariidae, or “eared” seals, which includes sea lions and fur seals. The otariids are not typically considered vocal learners, and neither are members of the third group of pinnipeds, the walruses (Odobenidae).
In other words, “true” seals and “eared” seals, which confusingly includes sea lions, diverged around 35 million years ago. That, according to Fitch, means that they are “about as different as cats and dogs.” True seals are vocal learners.
So are sea lions vocal learners or aren’t they? We’ll come back to that in a moment.
First, I would be remiss if I did not point out that while it might make for a snappy headline, Ronan is by no means the first non-human mammal to show evidence of dancing. A 2009 paper by animal cognition researchers found dancing in at least four Asian elephants. Sorry, Ronan.
Still, Ronan’s performance is – potentially – a big blow to Patel’s “vocal learning and rhythmic synchronization hypothesis.” But not as big a blow as a chimpanzee named Ai.
Research published last week in the open-access journal Nature Scientific Reports provided convincing evidence that a 36-year-old female chimpanzee named Ai was able to tap her finger in sync with a beat. Two other chimpanzees, 12-year-old male Ayumu and 12-year-old female Cleo, were unable to sync their tapping with a beat. Still if Patel’s hypothesis was right, then Ai shouldn’t have been able to do this.
The truth is, though, that Ai’s performance was a bit weak. For one thing, she wasn’t able to to synchronize her finger tapping at multiple rates. Humans, for example, are able to synchronize their tapping to rates between 200 and 1800 milliseconds, while Ai was only successful at 600 ms. And while it passed statistical significance, her accuracy wasn’t as good as it could have been.
Most damaging, however, was that there wasn’t conclusive evidence that Ai’s synchronized tapping was the result of entrainment of her motor system to the beat, because the keyboard she was tapping made sounds when the keys were tapped. That means it is possible that Ai just synchronized the sound of the piano with the rhythm, much like musicians do with a metronome, rather than explicitly synchronizing her behavior itself with the rhythm.
What of Patel’s vocal learning and rhythmic synchronization hypothesis? Neither Ronan nor Ai is enough to completely shatter it. Here are some possibilities.
First, Ronan and Ai may simply be extraordinary individuals from among their respective species. Perhaps they’re even capable of vocal learning, at least in a limited way. While this is unlikely, it would leave Patel’s hypothesis intact.
Second, perhaps any animal with sufficient training can learn rhythmic entrainment. While damaging to the vocal learning hypothesis, it would just shift the goalposts slightly – what is it about humans, songbirds, parrots, and the rest that allows them to do this so easily and so flexibly, without extensive training?
There’s a third possibility. I promised to return to the question of whether sea lions are vocal learners, and here is the answer. Perhaps the distinction between vocal learners and non-learners needs to be re-thought. Indeed, the strict dichotomy between vocal learners and non-learners is probably a bit too simplistic to describe biological variation anyway. Perhaps sea lions and chimpanzees (and mice?) lie somewhere in between complete non-mimics like rhesus monkeys and true vocal learners, like humans, parrots, elephants, and the rest of their dance partners. If this is the case, and I believe it is, then the question becomes how sophisticated must vocal learning be before a given species is able to predictably demonstrate dancing ability?
No single scientific experiment provides the last word on anything. Ronan and Ai don’t completely eviscerate Patel’s vocal learning hypothesis, but combined they pose a challenge that must be addressed. That’s how science works. Someone puts forth a hypothesis, and others vigorously try to break it. If they succeed, then after multiple independent replications, the hypothesis needs to be modified. And that’s a far more interesting story than “sea lion learns to dance.” It’s one that plays out over generations with multiple protagonists and plot twists.
Cook P., Rouse A., Wilson M. & Reichmuth C. (2013). A California Sea Lion (Zalophus californianus) Can Keep the Beat: Motor Entrainment to Rhythmic Auditory Stimuli in a Non Vocal Mimic., Journal of Comparative Psychology, DOI: 10.1037/a0032345
Hattori Y., Tomonaga M. & Matsuzawa T. (2013). Spontaneous synchronized tapping to an auditory rhythm in a chimpanzee, Scientific Reports, 3 DOI: 10.1038/srep01566
Patel A.D. (2006). Musical Rhythm, Linguistic Rhythm, and Human Evolution, Music Perception, 24 (1) 99-104. DOI: 10.1525/mp.2006.24.1.99
For more on music and dancing:
Are Humans The Only Species That Enjoy Dancing
Singing Mice Might Join Humans and Songbirds as Vocal Learners
Adventures in Pedantry: Fringe’s Captain Windmark Can’t Be A Toe-Tapper
Day Old Chickens Prefer The Same Music That You Do
For more on pinnipeds:
Forget Elephants. Sea Lions Never Forget!
Ronan photo via Pinniped Cognition and Sensory Systems Laboratory