Global cultural evolutionary model of humpback whale song

Humpback whale song is an extraordinary example of vocal cultural behaviour. In northern popula-tions, the complex songs show long-lasting traditions that slowly evolve, while in the South Pacific, pe-riodic revolutions occur when songs are adopted from neighbouring populations and rapidly spread. In this species, vocal learning cannot be studied in the laboratory, learning is instead inferred from the songs’ complexity and patterns of transmission. Here, we used individual-based cultural evolutionary simulations of the entire Southern and Northern Hemisphere humpback whale populations to formalise this process of inference. We modelled processes of song mutation and patterns of contact among popu-lations and compared our model with patterns of song theme sharing measured in South Pacific popula-tions. Low levels of mutation in combination with rare population interactions were sufficient to closely fit the pattern of diversity in the South Pacific, including the distinctive pattern of West-to-East revolu-tions. Interestingly, the same learning parameters that gave rise to revolutions in the Southern Hemi-sphere simulations gave rise to evolutionary patterns of cultural evolution in the Northern Hemisphere populations. Our study demonstrates how cultural evolutionary approaches can be used to make infer-ences about the learning processes underlying cultural transmission and how they might generate emergent population-level processes.