PARIS - Of all the music styles to emerge in the last 50 years, none took the world by storm quite like hip-hop, said researchers Wednesday who tracked pop's evolution with cold, hard stats.
More than disco, funk or heavy metal, hip-hop and its spinoff rap appear "to be the single most important event that has shaped the musical structure of the American charts in the period that we studied," said their report.
Born as a form of expression for disenfranchised youth in New York City's borough the Bronx, the arrival of hip-hop creates a large spike on a series of graphics illustrating the research findings, carried by the journal Royal Society Open Science.
It peaks in 1991, when artists like LL Cool J burst onto the scene.
"Hip-hop just sort of blasts out of nowhere," lead study author Armand Leroi, an evolutionary biologist with Imperial College London, told AFP.
"In retrospect it was there all along, it was there since the '80s bubbling underneath the chart down there wherever hip-hop came from in the streets of New York and Los Angeles. And then suddenly it goes mainstream and it's all over the charts."
Leroi and Matthias Mauch, an informatics researcher at the Queen Mary University of London, used algorithms and computer analysis to observe changing trends in pop music from 1960 to 2010.
They used about 17,000 songs on the US Billboard Hot 100, analysing characteristics like the frequency of certain chords, instruments or voice types, whether a song was calm or energetic, and whether it used speech or singing vocals.
Songs scored "average" from different years were compared to one another to see how much they differed.
"Actually for the most part, unsurprisingly, the songs of one year are usually pretty much like the songs of the next year," said Leroi.
"But there are some times when that distance, that difference, becomes bigger and you have a bunch of years suddenly all sorts of things are changing and those are the years around which we identify the revolutions."
Three such "revolutions" were pinpointed -- in 1964, 1983 and 1991 -- and the last was by far the biggest.
"We ask what's happening there, and for '91 it's very clear: it's hip-hop that's happening," Leroi said -- with a spike in songs featuring "no chords" and "energetic speech".
The 1964 revolution was marked by the expansion of several styles at once, said the study -- soul, rock and doo wop among them.
And the 1983 spike was marked by new wave, disco and hard rock.
For Mauch, the study provides rare scientific data on the evolution of pop.
"It is a mainstay of pundits and some scientists that music has become more uniform," he said. "On our particular dataset, we could not observe this."
The researchers' method could be used to measure the evolution of any form of cultural expression that can be digitised -- texts, paintings or films -- in order to analyse and understand trends.
"Culture is not anymore about music critics and art critics telling us the way it was, its going to be about scientists telling us about what the actual patterns are," said Leroi.
"From here, we want to understand the forces that have actually shaped things. Now that we get a grip on patterns, we want to know... why."