Seals have a sense of rhythm

Rhythm is important to human music and speech. But are we the only mammal with a sense of rhythm? In an experimental study published in Biology Letters, a team of researchers led by the Max Planck Institute for Psycholinguistics in Nijmegen and the Sealcentre Pieterburen show that seals can distinguish rhythm without prior training. The seals’ rhythmic ability may be linked to their ability to learn vocalizations, skills that may have co-evolved in both humans and seals.

Why are we such chatty, musical animals? Evolutionary biologists think our abilities for speech and music may be linked: Only animals that can learn new sounds—like humans and songbirds—seem to have a sense of rhythm. “We know that our closest relatives, nonhuman primates, have to be trained to respond to rhythm,” explains first author Laura Verga. “And even when trained, primates show very different rhythmic abilities than ours.” But what about other mammals?

Stamp rate

The researchers decided to test the rhythmic abilities of harbor seals, animals known to be capable of vocal learning. The team created sequences of seal vocalizations for the first time. Sequences differed in three rhythmic properties: tempo (fast or slow, such as beats per minute in music), length (short or long, such as the duration of musical notes), and regularity (regular or irregular, such as a metronome vs. free beat jazz). Would baby seals respond to these rhythmic patterns?

The team examined twenty young seals held in a rehabilitation center (the Dutch Sealcentre Pieterburen) before being released into the wild. Using a method from studies of human infants, the team recorded how many times the seals turned their heads to look at the source of the sound (behind their backs). Such behavior indicates whether animals (or infants) find a stimulus interesting. If seals can discriminate between different rhythmic properties, they may appear longer or more frequent when hearing a sequence they prefer.

Seals looked more often when voices were louder, faster, or rhythmically regular. This means that the one-year-old child—without training or rewards—spontaneously discriminates between regular (metronomic) and irregular (arrhythmic) sequences, short vs. long note sequences, and fast vs. slow tempo sequences.

Evolutionary origins

“Another mammal, besides us, shows rhythm processing and vocal learning,” says Verga. “This is an important advance in the debate about the evolutionary origins of human speech and musicality, which is still rather mysterious. Like human babies, the sense of rhythm we find in seals appears early in life, is robust, and does not it requires neither training nor reinforcement.”

Next, Verga and her team want to know if the seals perceive rhythm in the vocalizations of other animals, or even abstract sounds. and whether other mammals show the same skills: “Are seals special, or are other mammals capable of spontaneously perceiving rhythm?”