Data from: Directional cultural change by modification and replacement of memes

Evolutionary approaches to culture remain contentious. A source of contention is that cultural mutation may be substantial and, if it drives cultural change, then current evolutionary models are not adequate. But we lack studies quantifying the contribution of mutations to directional cultural change. We estimated the contribution of one type of cultural mutations – modification of memes - to directional cultural change using an amenable study system: learned birdsongs in a species that recently entered an urban habitat. Many songbirds have higher minimum song frequency in cities, to alleviate masking by low-frequency noise. We estimated that the input of meme modifications in an urban songbird population explains about half the extent of the population divergence in song frequency. This contribution of cultural mutations is large, but insufficient to explain the entire population divergence. The remaining divergence is due to selection of memes or creation of new memes. We conclude that the input of cultural mutations can be quantitatively important, unlike in genetic evolution, and that it operates together with other mechanisms of cultural evolution. For this and other traits where the input of cultural mutations might be important, quantitative studies of cultural mutation are necessary to calibrate realistic models of cultural evolution.有关文化演化的研究范式至今仍颇具争议。争议的核心焦点之一在于：文化突变（cultural mutation）的幅度可能十分可观，若其驱动了文化变迁，则现有的演化模型已不足以适配相关研究。但目前学界尚缺乏量化突变对定向文化变迁贡献度的相关研究。本研究借助新近进入城市生境的某一鸟类物种的习得性鸣唱这一易于开展研究的实验体系，对一类文化突变——即模因（meme）的修饰——在定向文化变迁中的贡献度进行了估算。诸多鸣禽在城市环境中的最低鸣唱频率更高，以此缓解低频噪声对鸣唱的掩蔽效应。我们估算发现：城市鸣禽种群中，由模因修饰所带来的文化输入，可解释该种群鸣唱频率分化程度的约一半。此类文化突变的贡献度虽较为显著，但仍不足以完全解释种群的整体分化。剩余的种群分化则源于模因的选择或新模因的产生。本研究得出结论：与遗传演化不同，文化突变的输入量可在量化层面发挥重要作用，且其与其他文化演化机制协同运作。针对此类以及其他可能受文化突变输入量影响显著的性状，开展文化突变的量化研究，对于校准贴合实际的文化演化模型而言至关必要。