Scientists have long pondered why humans are such chatty, musical animals. Evolutionary biologists believe that our capacities for speech and music may be linked, since only animals that can learn new vocalizations, such as humans or songbirds, appear to have a sense of rhythm.
Now, a team of researchers led by the Max Planck Institute for Psycholinguistics has tested the rhythmic abilities of harbor seals, a species of animals known to be capable of rhythmic learning. The analyses revealed that seals also have a sense of rhythm, being able to discriminate between rhythmic and non-rhythmic sequences early in life, without any training or rewards.
The researchers tested 20 young seals from a rehabilitation center in the Netherlands, before they were released in the wild. First, the team created several sequences of seal vocalizations which differed in three rhythmic properties: tempo (fast or slow, such as beats per minute in music), length (short or long, like the duration of musical notes), and regularity (regular or irregular, as in the case of a metronome versus the rhythm of improvisational jazz). Then, by using a method derived from human infant studies, the scientists recorded how many times the seals turned their head to look at the sound source – a behavior indicating whether animals find a stimulus interesting.
The seals looked at the stimulus more often when vocalizations were longer, faster, or rhythmically regular. This suggests that one-year-old seals can spontaneously discriminate between regular (metronomic) and irregular (arrhythmic) sequences, as well as between sequences with short versus long notes, and sequences with fast versus slow-paced tempo.
“Another mammal, apart from us, shows rhythm processing and vocalization learning,” said study lead author Laura Verga, a postdoctoral fellow in Comparative Bioacoustics at Max Planck. “This is a significant advance in the debate over the evolutionary origins of human speech and musicality, which are still rather mysterious. Similarly to human babies, the rhythm perception we find in seals arises early in life, is robust and requires neither training nor reinforcement.”
In future studies, Dr. Verga and her colleagues aim to explore whether seals perceive rhythm in vocalizations of other animals, or even when hearing abstract sounds, as well as whether other mammals have similar capacities.
The study is published in the journal Biology Letters.
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