For all the world’s linguistic diversity, human languages still obey certain universal patterns. These run deeper than grammar and syntax; they’re rooted in statistical laws that predict how frequently we use certain words and how long those words tend to be. Think of them as built-in guardrails to keep language easy to learn and use.
Now scientists have found some of the same patterns in whale vocalizations. Two new studies show that humans and whales have converged on similar solutions to the problem of communicating through sound. “It strengthens the view that we should not be thinking about human language as a completely different phenomenon from other communication systems but instead we should be thinking about what it shares with them,” says Inbal Arnon, a psychologist at the Hebrew University of Jerusalem and co-author of one of the studies.
For a paper in Science, Arnon and her colleagues analyzed humpback whale songs recorded over eight years in New Caledonia in the South Pacific and found that they closely adhered to a principle called Zipf’s law of frequency. This mathematical power law, a hallmark of human language, is observed in our word-use frequencies: the most common word in any language shows up twice as often as the second-most common, three times as often as the third, and so on.
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Listen to the humpback whale songs:
But before the researchers could analyze the recordings, they had to identify the segments that were analogous to words (though without semantic meaning) in a stream of otherworldly grunts, shrieks and moans. The scientists found themselves in the same predicament as a newborn baby—so, naturally, that’s where they turned for guidance. Human infants “get this continuous acoustic signal,” Arnon says, “and they have to figure out where the words are.”
A human baby’s strategy is simple: listen for unexpected combinations of sounds in adult speech. Whenever you identify one, you’ve probably located a boundary between words, because those uncommon transitions are less likely to occur within words.
When the researchers segmented whale songs based on these “transitional probabilities”—just as a human infant would—Zipf’s law of frequency fit the sounds like a glove. And 1,000 arbitrarily shuffled elements of the data came nowhere near a match, strongly suggesting the transitional-probability results weren’t a product of random chance. “We were all dumbfounded,” says co-author Ellen C. Garland, a whale-song expert at the University of St. Andrews in Scotland. “There was the possibility of discovering these same structures. Did we think we would? Hell, no.”
Why would the same communicative behaviors evolve independently in whales and humans, whose last common ancestor was a potentially shrewlike creature that lived roughly 100 million years ago? Word distribution according to Zipf’s law of frequency seems to help infants grasp language—and some linguists theorize that such learnability leads to the distribution’s development. “When things are organized that way in your input, you’re going to learn them better,” says study co-author Simon Kirby, a cognitive scientist at the University of Edinburgh.
In other words, the structure of language may be largely a product of how it gets passed from one generation to the next. So the team reasoned that Zipf’s law of frequency might appear not just in human language but also among any other animals whose sequential vocal signals are culturally learned (transmitted between individuals). That group encompasses what Kirby calls “a strange, ragtag bunch of species,” including songbirds, bats, elephants, seals, dolphins and whales. Most other animals that communicate vocally—from dogs to frogs to fish—are thought to use signals that are genetically programmed, not learned.
We now know that whales, at least, share a key ingredient of our own communication system, a finding that fits with the growing attitude among scientists that we aren’t as unique as we once thought. Instead our linguistic capacity rests on a smorgasbord of physical and cognitive traits, many of them spread throughout the animal kingdom.
In a separate paper published in Science Advances, Mason Youngblood, a postdoctoral fellow at Stony Brook University, reports evidence of two more language laws in whale vocalizations: One is the brevity law, which, when applied to human language, states that the more common a word is, the shorter it tends to be, and vice versa. The other is Menzerath’s law, which says the longer a linguistic construct (such as a sentence) is, the shorter its constituent parts (such as a sentence’s clauses) will be.
Youngblood found that both patterns were especially strong in humpback song but showed up in other whale species, too. These laws describe how animals “maximize the amount of information they convey in the least amount of time and with the least amount of energy,” he says.
As tempting as the comparisons with human language may be, the researchers caution against reading too much into these parallels. “Whale song is not a language,” Garland says flatly. Although whale calls clearly carry some kind of meaning, she notes that most experts see little resemblance to the depth and complexity of human language. Most important, humpback sounds can’t be recombined in endless different ways to express new ideas—an entire song clearly conveys something, but the “words” within it seem to lack independent meaning. In that way, whale song is more like music, which also happens to follow Zipf’s law.
But the similarities are still striking. Luke Rendell, a biologist at the University of St. Andrews, who was not involved with either study, says these findings could be “telling us something kind of profound about how evolution can either converge at or, perhaps, be constrained to certain types of learning.” That is, they might inform us about the range of possibilities for complex communication in any species.
By the same token, Kirby suggests that Zipf’s law, and perhaps other linguistic laws, could be “a kind of fingerprint of these culturally evolved systems,” present wherever animals have crossed the threshold of cultural learning. “It’s probably a very fundamental feature of the organization of cognitive systems,” he adds.