The Population Memetics of Bird Song
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Two basic requirements for a theory of evolution are variability and heritability in the units of change. These requirements are fulfilled in cultural systems, and therefore it is possible to construct a theory of cultural evolution. In many species of birds, song is aquired by social learning, and bird song is often cited as one of the best examples of a culturally aquired trait in animals. As such, it provides a good subject to develop a model of cultural evolution.
In this paper I examine patterns of differentiation of bird songs within an evolutionary framework. I identify analogues of the evolutionary forces responsible for frequency changes (mutation, migration, drift and selection) and adopt methods of population genetics to estimate parameters of population structure and determine the factors responsible for the origin an maintenace of song diversity within and between populations.
The levels of memetic diversity within populations in a number of songbird species seem to be consistent with a random drift-migration-mutation model. I tentatively postulate that each species has a potential mutation rate that is adjusted in different populations according to the acoustic properties of the environment. In this scenario, then, the main importance of selection is t weed out unsuitable types that appear by mutation or immigration. In general, populations will tend to diverge randomly because normal levels of meme flow are not high enough to prevent the accumulation of new variants in different populations that result from the high rates of meme mutation. If the acoustic environment changes, however, or if individuals of a given population colonize a new habitat with different acoustic properties, then directional selection can act on the neutral or nearly neutral variants already in the population.