Male humpback whales (Megaptera novaeangliae) produce population-specific songs that evolve rapidly and are socially transmitted, ensuring song conformity at any time. While the evolution of song has been well described across many populations, the mechanisms driving this remain unclear. The rapid social learning of evolutionary changes, however, may be assisted if it follows rules for temporal change. Here, we test this hypothesis by examining structural changes during song evolution in two humpback whale populations from western and eastern Australia. We quantified and compared songs over 9 years. On multiple occasions, song themes spread from the western to eastern population, then continued to evolve independently, allowing comparison of the evolution of the same themes in two different populations. Phrases (repeated song segments comprised of different units) were analysed for changes in (1) the number of units, (2) unit types, and (3) duration. Additionally, we examined whether individual units within shared themes retained acoustic similarities as they evolved. Shared themes diverged markedly between populations, suggesting that song evolution is not guided by a set of rules. These findings highlight the flexible, dynamic nature of vocal production learning in humpback whales. Understanding these processes is key to uncovering the broader mechanisms underpinning the evolution of complex communication systems.
Williams et al. (2025) studied this question.