In modern societies, cultural change appears to be continuous. The flow of fashion is especially evident for folk music. While much has been written about the origin and development of pop music, most claims about its history are anecdotal rather than scientific in nature.

We investigated the US Billboard Hot 100 between 1960 and 2010. Using musical information retrieval and text mining tools, we analyze the musical properties of approximately 17,000 recordings that appeared in charts and show quantitative trends in their consistency and timelines Properties. We then use these characteristics to produce an acoustic classification of musical styles and to study the evolution of musical diversity and variance, and to test and reject many classic theories of cultural change.

Finally, we investigate whether pop musical development was gradual or choppy. We show that although the pop music has continuously evolved, it did so that particularly quickly during three stylistic “revolutions” around 1964, 1983, and 1991. We conclude by discussing how our study points the way to the quantitative science of cultural change.

The history of the popular music has long been debated by philosophers, sociologists, journalists, bloggers, and pop stars. Although their accounts are rich in lively musical traditions and aesthetic judgments, they lack what scholars want: rigorous tests of clear hypotheses based on data and quantitative statistics. Economics sociologists who study the history of music have done better, but are less interested in music than the means by which it is marketed. The contrast with evolutionary biology—a historical science rich in quantitative data and models—is striking, especially since cultural and organic diversity are considered to be the result of modifications by lineage. In fact, linguists and archaeologists, who study the evolution of languages   and material culture, apply the same tools that evolutionary biologists use when studying the evolution of species.

Until recently, the biggest impediment to a scholarly account of musical history was the lack of data. That has changed with the advent of large, digital collections of audio recordings, notes, and lyrics. Quantitative studies of musical development followed quickly. Here, we use a collection of digital music to research the history of American popular music. Drawing inspiration from studies of organic and cultural evolution, we look at pop music history as a “fossil record” and ask the kinds of questions a paleontologist might have: Has the diversity of popular music increased or decreased over time? Is evolutionary change in popular music continuous or sporadic? And if it is intermittent, when did the interruptions occur?

Like previous studies of pop music history, ours is based on features extracted from sound rather than findings. However, as these early studies focused on technical aspects of sound such as loudness, vocabulary statistics, and sequential complexity, we have attempted to identify features with musical meaning. To this end, we have adopted an approach inspired by recent developments in text mining. We began by measuring our songs for a series of quantitative phonemic features, 12 descriptors of tonal content and 14 timbres (electronics supplementary material, M2–3). They were then categorized into ‘words’ resulting in a harmonic lexicon (H lexicon) for chord changes, and a timbre lexicon (T lexicon) for timbre combinations (Supplementary Electronic Material, M4).