Culture was once thought to be what distinguishes humans from other animals. However, research by a University of St Andrews-led team of scientists studying behavior of humpback whales and other animals tells a radically different story.
Humpback whales (Megaptera novaeangliae) in the South Bank, Dominican Republic. Image credit: Christopher Michel / CC BY 2.0.
Adult male humpback whales (Megaptera novaeangliae) produce a long, complex, and stereotyped song on low-latitude breeding grounds. They also sing while migrating to and from these locations, and occasionally in high-latitude summer feeding areas.
All males within a population adhere to the current content and arrangement of the song.
The song is organized in a nested hierarchy: single sounds are termed ‘units,’ a sequence of units is grouped into a ‘phrase,’ phrases are repeated to form a ‘theme,’ and a number of different themes are usually sung in a set order to form the ‘song.’
In an earlier study, Dr. Ellen Garland from the University of St Andrews School of Biology and co-authors discovered an extraordinary cultural phenomenon in the humpback whale songs.
Around Australia, some new songs would emerge and quickly become popular, being shared by all nearby whales.
This new song would then be transmitted eastwards across the South Pacific Ocean, traveling right across to French Polynesia over the next year.
In later years, more songs followed in this way, passing in waves across the ocean.
Now, the team has been able to track exactly how the change from old to new songs occurs, revealing details of how evolution works within such animal cultures.
The researchers investigated rare cases of song hybridization, found among thousands of hours of song from the South Pacific, where parts of an existing song were spliced with a new one, and likely prior to an individual whale totally adopting the new song.
“Song unit sequences were extracted from over 9,300 phrases recorded during two song revolutions across the South Pacific Ocean, allowing fine-scale analysis of composition and sequencing,” they explained.
The authors identified two different kinds of structural rules guiding song change.
In one, a whale sings some of the old and some of the new song, making a transition between them with a kind of short hybrid ‘phrase.’
In the other approach they may splice into their current song a whole ‘theme’ from the new song others are beginning to sing.
“These rare glimpses into the underlying learning mechanisms show that songs appear to be learnt as segments, reminiscent of the way children acquire language,” Dr. Garland said.
“Humpback whales provide a unique perspective for understanding of animal culture,” the scientists said.
“Their mammalian heritage also makes them particularly important to our understanding of structurally arranged vocal communication and the potential origins of human language.”
“In this study, by investigating rare cases of song hybridization, where parts of an existing song are spliced with a novel, revolutionary song, we have unearthed a number of underlying structural rules governing song change, including segmentation and transition/substitution of themes based on the similarity in sound sequences.”
“These rules likely assist humpback whales in rapidly learning their complex and ever-changing songs, and provide insights into the evolution of human language and culture,” they concluded.
The findings appear in a special edition of the Proceedings of the National Academy of Sciences, ‘The Extension of Biology through Culture,’ published this week.
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Ellen C. Garland et al. 2017. Song hybridization events during revolutionary song change provide insights into cultural transmission in humpback whales. PNAS 114 (30): 7822-7829; doi: 10.1073/pnas.1621072114
