CHICAGO -- Why dogs can't dance but sea lions can came under intense scrutiny by a panel of experts at the AAAS Annual Meeting.
"Understanding to what extent different animal species can move in time to a musical beat may help us better understand how our own capacity to enjoy music evolved," said Annirudh Patel, an associate professor of psychology at Tufts University, who spoke at a symposium  on 15 February.
Humans have moved in time to music since the age of hunter-gatherers. English naturalist Charles Darwin proposed that a sense of rhythm is inherent to all living organisms. "[It] is probably common to all animals, and no doubt depends on the common physiological nature of their nervous systems," he wrote in The Descent of Man, and Selection in Relation to Sex.
Yet recent research has challenged this view, suggesting that the capacity to "entrain" is more limited. While animals rather distant from humans, such as parrots, have shown a knack for it, the rhythmic capabilities of humans' closest relatives, including other apes, remain intensely debated.
Patel is part of the first research team to show that a nonhuman organism can beat-match to a melody. He worked with Snowball, a dancing cockatoo, and his findings support the so-called "vocal learning and synchronization hypothesis." It suggests that only those species that vocally mimic, like cockatoos, are capable of aligning their movements to music. This is because the same neural pathways that evolved to support vocal mimicry allow animals to perceive and move to music, or so the hypothesis goes.
If true, this hypothesis has broad implications, suggesting that the capacity for music cognition isn't common across all species, based on a fundamental part of brain anatomy. Rather, it evolved separately in different species, such as humans and cockatoos, through series of neural changes.
Scientists have had difficulty disputing this hypothesis, because until recently there was no published evidence of animals that aren't vocal mimics tapping in time to a beat. Last year, however, Emory University comparative psychologist Peter Cook published a paper showing that a sea lion -- an animal with no vocal mimicry -- abilities, could entrain to music.
"She really liked dancing to Boogie Wonderland," Cook said. In one experiment, he changed the tempo of Boogie Wonderland five times, and in each instance, Ronan, the sea lion he trained, could bop along. This is the first case of a non-human mammal demonstrating such a capacity. "It suggests the ability to move to a beat may be more widespread in the animal kingdom than we thought," Cook said.
Though Cook's find is in a non-vocal mimic and thus seems to bring the vocal learning and synchronization hypothesis into question, Patel doesn't think it conclusively refutes it. "We need further studies to test the hypothesis," he emphasized.
Further studies are indeed happening in this young field, including studies aimed to more rigorously test whether a mammal can synchronize its movements to sounds at different tempos.
Patricia Gray, director of the biomusic program at the University of North Carolina at Greensboro, is working with bonobos. "They are among humans' closest living relatives, with similar brain mechanisms, so it makes sense to study their rhythmic perceptions," she said.
Dr. Gray is teasing out tempos at which bonobos match their drumbeats to those of humans drumming. She went to great lengths to ensure the correct conditions for this research, something previous experiments have neglected.
"To gain and sustain the bonobos' interest," she said, "we worked with the Remo Drum Company to design a drum that is ergonomically appropriate for these animals. We didn't just use inverted buckets like previous research attempts."
Using new methods and techniques, Dr. Gray is gaining new insights into bonobos' temporal coordination abilities. She's learning that the social aspect - bonobos learning alongside a human counterpart who demonstrates what to do - is critical to these animals' success. "This work could contribute greatly to our understanding of social cognition and the evolution of speech and music," she said.
Connecticut University's Edward Large, a professor in the department of psychology and physics, also works with bonobos. He aims to show what factors, including frequencies of auditory information, are most important in the evolution of animal communication systems.
These and other studies may help scientists better grasp how animals evolved to process complicated sounds, shedding light on animal communication systems, including human speech.