The results of the evolution of western pop music, spanning from 1960 to 2010, was published in The Royal Society Open Science Journal. The scientists who looked at more than 17,000 songs found three music revolutions – in 1964, 1983 and 1991. In 1964 the invasion of British bands introduced a radical new rocky sound. Synthesisers, samplers and drum machines, drove a second major style shift in 1983. The third, in 1991, came about when rap and hip-hop went mainstream. The team also refuted claims that pop music was starting to sound the same.