Humpback whales sing the way humans speak

New York: The English language is full of wonderful words, from “anemone” and “aurora” to “zenith” and “zodiac”.

But these are special-occasion words, sprinkled sparingly into writing and conversation. The words in heaviest rotation are short and mundane. And they follow a remarkable statistical rule, which is universal in human languages: the most common word, which in English is “the”, is used about twice as frequently as the second most common word (“of”, in English), three times as frequently as the third most common word (“and”), continuing in that pattern.

An international, interdisciplinary team of scientists has now found that the intricate songs of humpback whales, which can spread rapidly from one population to another, follow the same rule, known as Zipf’s law.

Male humpback whales sing long, elaborate songs, which are composed of a variety of sounds strung together in repeated phrases and themes.Credit: Jonas Liebschner/Whale Watching Sydney

The scientists are careful to note that whale song is not equivalent to human language. But the findings, they argue, suggest that forms of vocal communication that are complex and culturally transmitted may have shared structural properties.

“We expect them to evolve to be easy to learn,” said Simon Kirby, an expert on language evolution at the University of Edinburgh and an author of the new study. The results were published on Friday (AEDT) in the journal Science.

“We think of language as this culturally evolving system that has to essentially be passed on by its hosts, which are humans,” he said. “What’s so gratifying for me is to see that same logic seems to also potentially apply to whale song.”

Zipf’s law, named for American linguist George Kingsley Zipf, holds that in any given language, the frequency of a word is inversely proportional to its rank.

There is still considerable debate over why this pattern exists and how meaningful it is. But some research suggests that this kind of skewed word distribution can make language easier to learn.

If these word distributions evolved because they helped learning, scientists might also expect to find similar patterns in other complex, culturally transmitted communications.

“And whale song is a great place to look,” said study co-author Inbal Arnon, an expert on language acquisition at Hebrew University in Jerusalem.

Male humpback whales sing long, elaborate songs, comprising various sounds in repeated phrases and themes. All the males in a particular humpback population sing the same song, but that song evolves over time – either gradually or instantaneously.

“We have song revolutions, and that’s when a song is introduced from a neighbouring population,” said co-author Ellen Garland, an expert on humpback whale songs at the University of St Andrews in Scotland.

“So the song type turns up, and then it completely takes over.”

Precisely how that happens remains a mystery, and whale song researchers face a challenge that human language researchers don’t: they’re not native speakers.

So the scientists’ first challenge was to divide the songs into meaningful units, determining where one “word” ended and another began. To do so, they took inspiration from human babies. Infants, research suggests, use basic statistical reasoning to identify discrete words in a continuous stream of human speech; syllables that occur together are likely to be part of the same word.

Whale song does not carry the same semantic meaning that human language does, says Ellen Garland, a co-author of the paper.Credit: Fairfax Media

The researchers transformed humpback whale songs, recorded over eight years near New Caledonia, into long sequences of basic sound elements, including various types of squeaks, grunts, whistles, groans and moans. They identified “sub-sequences” of sounds that frequently occurred together – such as a short ascending whistle, then a squeak – and that might be roughly analogous to a word.

The frequency with which these sub-sequences were used followed Zipf’s law, the researchers found. In 2010, for instance, groan-groan-moan was the most common sub-sequence, appearing about twice as often as the next most common sequence, which was a moan followed by three ascending cries. The most frequently used sub-sequences were also generally shorter than the rarer ones.

Humans and humpback whales were not closely related, and whale song did not carry the same semantic meaning that human language did, Garland said. But both means of communication were culturally transmitted, learnt from others in the community and passed down over generations.

“So this really points to the crucial role of learning and transmission in the emergence of structure,” she said.

Shane Gero, a marine biologist who was not involved in the research, said he found the study elegant and convincing. The results raised the possibility that linguistic laws derived from studies of human communication might actually be broader biological principles, he said.

“Anytime we look deeper and listen longer, we find interesting complexity.” said Gero, a scientist-in-residence at Carleton University in Ontario, Canada.

The next step is to determine whether the phenomenon extends to other animals with similar communication systems.

“We should find these statistical properties in any culturally transmitted system of sequential signalling,” Arnon said. “So we have bats to look at, we have songbirds to look at, we have elephants, maybe, to look at.”

The findings dovetail with another paper published last week, which found that the vocalisations produced by 11 species of dolphins and whales followed one of the efficiency rules observed in human language. The rule, known as Menzerath’s law, holds that the longer a sequence becomes, the shorter its individual components tend to be; long sentences, for instance, tend to have shorter words.

The study, published in Science Advances, documented this same pattern in a diverse array of cetaceans, including humpbacks, which produce melodic songs; sperm whales, which issue sequences of clicks; and bottlenose dolphins, which are known for their whistles.

“Regardless of what their vocalisations are used for, they all seem to try to communicate as efficiently as they can,” said study author Mason Youngblood, a postdoctoral researcher at the State University of New York.

The pattern, also documented in birds and non-human primates, may have evolved as a way to reduce the costs of communication.

“Things like bird song and whale song are very hard to learn,” Youngblood said.

“And then when you sing, it’s very energetically costly. It can attract the attention of predators. And so because of that, you would expect communication systems to evolve to cut those costs wherever it’s possible.”

This article originally appeared in The New York Times.

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