A new paper in Current Biology, published today has revealed that the songs of Humpbacked Whales are passed through the ocean by mechanisms of cultural transmission.
Cultural transmission is defined as the social learning of information or behaviours either over generations or via peers. It has been seen to occur in primates, cetaceans and birds.
Cultural transmission over generations, i.e. parent passing socially learnt traits to their offspring, is known as vertical transmission and cultural transmission via peers, unrelated individuals from within generations, is known as horizontal transmission. In humans, languages and memes are transmitted, learned and (in a lot of cases) evolved in this manner.
Male humpback whales have a repetitive and evolving ‘song’ which acts as a vocal sexual display. This song is highly repetitive and is used, by mechanisms of social sorting and attraction, to allow for sexual selection within the whale population. All males within a population are known to conform to the current version of the display (song type), and similarities have been seen to exist among the songs of populations within an ocean basin.
The study being discussed presents very strong evidence for patterns of horizontal transmission, whereby song types spread unidirectionally and rapidly in the pacific ocean eastward through populations in the western and central South Pacific. The study was done over an 11-year period. This is the first documentation of a repeated, dynamic cultural evolution occurring across multiple populations at such a large geographic scale and across such a large time scale.
The patterns of cultural transmission seen in these whales songs are analogous to the same mechanisms we see in humans given that the songs are subject to mistakes and changes which are replicated. This causes the same mechanisms we see in the cultural transmission of language. The authors note that the level and rate of change seen in the whales is unparalleled in any other nonhuman animal and involves culturally driven change at a vast scale.
They also state that:
Investigating the underlying mechanisms of song evolution may yield powerful insights into the transmission of cultural traits and the evolution of culture and plasticity in sexually selected traits.
They also observed that at least one of the song types was transmitted between two different ocean basins, the Indian and South Pacific Ocean. It’s amazing to think how far a single song type can be horizontally transmitted.
Humpback whale song is unique among the animal kingdom due to the conformity to the current norm. This is coupled with high plasticity in the trait (ability to change their song based on whatever the new ‘norm’ is). Why both plasticity and conformity might be selected, how these interact with sexual selection, and how cultural evolution influences both are intriguing questions in need of consideration.
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