ROBERT SIEGEL, HOST:
Now a pop lesson - the evolution of pop music.
(SOUNDBITE OF SONG, "THE TWIST")
CHUBBY CHECKER: (Singing) Come on, baby. Let's do the twist.
SIEGEL: When you do the twist, it's to the dominant seventh chord which was a very dominant chord in the 1960s.
MELISSA BLOCK, HOST:
A research team at Queen Mary University of London analyzed pop music the way evolutionary biologists study organisms. To do this, they studied more than 17,000 songs that made the U.S. Billboard Hot 100 from 1960 to 2010.
MATTHIAS MAUCH: If you look at the charts as an ecosystem, we can see that the charts change all the time. They change in terms of harmony, in terms of timbre, sound color.
SIEGEL: That's Matthias Mauch, one of the authors of the study. His team noticed that certain chords would disappear as certain genres rose and fell in popularity - disco and rock, for example. He says it's similar to natural selection in the biological world.
MAUCH: Essentially, what's happening is that some musical ideas for one reason or another seem more appealing than others to composers and songwriters to reuse in their next song.
BLOCK: So when Elvis was singing the blues, that dominant seventh chord was largely in play. Mauch had his guitar ready to demonstrate for us.
(SOUNDBITE OF MAJOR CHORD ON GUITAR)
MAUCH: This is the major chord and if I change something...
(SOUNDBITE OF DOMINANT SEVENTH CHORD ON GUITAR)
MAUCH: ...Then I get the seventh that makes this chord a dominant seventh chord. And you get (singing) I feel so bad.
(SOUNDBITE OF SONG, "I FEEL SO BAD")
ELVIS PRESLEY: (Singing) I feel so bad, I feel like a ballgame on a rainy day.
SIEGEL: But then came the British invasion.
(SOUNDBITE OF SONG, "GET OUT OF MY CLOUD")
THE ROLLING STONES: (Singing) Hey, you, get out of my cloud.
MAUCH: We noticed that in '63, there was a lot of more aggressive guitar sounds coming in and also more major chords being used instead of the bluesy chords.
BLOCK: And soon after, enter the dreaded disco era.
MAUCH: And then we see a lot of minor seventh chords because they are very prominent in disco recording such as the Bee Gees "Night Fever." So, you know, that (singing) night fever, night fever.
(SOUNDBITE OF SONG, "NIGHT FEVER")
BEE GEES: (Singing) Night fever, night fever. We know how to show it.
BLOCK: By the time rap and hip-hop came on the scene, those chords have faded. Remember Tone Loc?
(SOUNDBITE OF SONG, "WILD THINGS")
TONE LOC: Let's do it.
MAUCH: What we see in rap recordings is obviously that they do not use very much harmony at all.
SIEGEL: As in nature, Mauch says earworms will keep on evolving. The next revolution could come at any time.
MAUCH: I don't know when it will happen. I don't even know actually whether it's already underway.
SIEGEL: And we all know that throwbacks are back in style.
(SOUNDBITE OF SONG, "HAPPY")
PHARRELL WILLIAMS: (Singing) It might seem crazy what I'm about to say.
MAUCH: The song "Happy" by Pharrell Williams uses a lot of minor seventh chords. Those are the ones that were introduced by disco essentially in the '70s, so they're still around.
(SOUNDBITE OF SONG, "HAPPY")
WILLIAMS: (Singing) Hot air balloon that could go to space.
BLOCK: Who are we kidding? Disco will never die.
(SOUNDBITE OF SONG, "HAPPY")
WILLIAMS: (Singing) With the air, like I don't care, baby, by the way because I'm happy.
SIEGEL: You're listening to ALL THINGS CONSIDERED from NPR News. Transcript provided by NPR, Copyright NPR.