Why are we such gregarious, musical creatures? According to evolutionary biologists, speech and musical abilities may be related because only animals that can learn new vocalizations, like humans and songbirds, appear to have a sense of rhythm. First author Laura Verga says, “We know that non-human primates—our closest relatives—need to be trained to respond to rhythm. Even when trained, primates exhibit rhythmic abilities that are quite different from ours. What about other mammals, though?
Seal rhythm
The scientists made the decision to examine the rhythmic aptitude of harbour seals, which are known to be vocal learners. The group initially recorded seal vocalization sequences. Three aspects of the rhythm in the sequences varied: regularity, pace (rapid or slow, like the beats per minute in music), and length (short or long, like the duration of musical notes) (regular or irregular, like a metronome vs. the rhythm of free jazz). Would young seals respond to these recurring rhythms?
Prior to their release into the wild, the researchers tested twenty juvenile seals housed at the Dutch Sealcentre Pieterburen. The team counted the number of times the seals rotated their heads to look at the sound source using a technique from studies on human infants (behind their backs). Such eye-gazing behavior reveals whether an object is attractive to animals or young children. If seals can tell the difference between different rhythms, they may search longer or more often when they hear a sequence they like.
When vocalizations were longer, quicker, or rhythmically regular, the seals turned their heads more frequently. In other words, the 1-year-old seals spontaneously distinguished between regular (metronomic) and irregular (arrhythmic) sequences; sequences with short vs. long notes; and sequences with fast vs. slow tempo, all without any training or rewards.
Evolutionary origins
Apart from us, another mammal exhibits rhythm processing and vocalization learning, according to Verga. “This represents a substantial advancement in the discussion surrounding the still somewhat enigmatic evolutionary origins of human speech and musicality. “Similar to young children, seals develop a strong sense of rhythm early in life without any teaching or reinforcement.”
Verga and her team’s next goal is to determine whether seals can detect rhythm in animal vocalizations or even in abstract sounds. Whether or not other mammals exhibit the same abilities, Are seals unique, or are other mammals also able to sense rhythm on their own?
