Flip through Rolling Stone, and you'll read about a lot of "revolutions" in popular music: Rock'n'roll and punk, disco and new wave. But for Matthias Mauch—an engineer at Queen Mary University of London—the qualitative analysis of musical evolution—the music critic's take—left him wondering: "Is there some way in which we could take this sort of pub conversation, and make it more quantifiable?"

So he and his colleagues analyzed fragments from more than 17,000 songs on the Billboard Hot 100, from 1960 to 2010. They processed the audio to extract information about timbral and harmonic qualities—tagging the files for attributes like "orchestra/harmonic" [mashup sample] or "calm/quiet/mellow." [mashup sample] Then they used those tags—which they compare to a musical "fossil record"—to tease out trends about musical evolution over time. 

Turns out, from 1960 to 2009, the dominant seventh chord [Elvis Presley—"I Feel So Bad"] all but disappeared in what they call the death of blues and jazz on the pop charts. But as dominant sevenths faded, the minor seventh came into its own… [KC and the Sunshine Band—"That's The Way (I Like It)"]... more than doubling in frequency between 1967 and '77. "We can really see the influx of funk, which is really turning into disco." [Bee Gees—"Night Fever"]

But next—as you know—come the '80s. Dominated by a rise in musical tags like "percussive" [The Cars—"Tonight She Comes"] and "guitar/aggressive" [Bon Jovi—"Bad Medicine"], the '80s were a low point for musical diversity. In fact 1986 stands out as the year that chart-topping songs sounded most alike.

"Then obviously the charts got saved in terms of diversity, by this new kid on the block, [Tone Loc—"Wild Thing"] the rap and hip-hop coming in. And then suddenly, boom: [LL Cool J—"Mama Said Knock You Out"] the diversity's back up and actually higher than before." The study appears in the journal Royal Society Open Science. [Matthias Mauch et al, The evolution of popular music: USA 1960–2010]

Of course, this big-data approach to pop culture probably won't overturn years of music scholarship. But the analysis does show that in the evolution of popular music, there really have been long periods of stasis, punctuated by periods of rapid change—musical revolutions—particularly in 1964, 1983 and 1991. And the more you study it, Matthias says, the more musical evolution starts to resemble plain old species evolution. "You take something that exists. And that in biology would be genes. But it's not genes here. You just take some styles. You recombine them, like genes are recombined, and you change them as well—a bit like mutation."

Who knows—maybe that might have been a better argument against copyright infringement for Robin Thicke and Pharrell Williams. "It's just evolution, your honor." [Marvin Gaye—Got to Give It Up / Robin Thicke—"Blurred Lines"]

—Christopher Intagliata 

[The above text is a transcript of this podcast.]