For each of those cultural “populations,” as the paper refers to them, the researchers identified scores of specific traits and characteristics, such as loud guitar and smooth harmonies in pop songs; engine power and wheelbase length in cars; various medical subjects in the BMJ; and topics such as “English aristocracy” and “grief and sorrow” in the novels.
They the team used advanced statistical methods to track the frequencies and values of those traits over time. The paper notes, for example, that loud guitars showed “a consistently high average frequency” and were still preserved in Lenny Kravitz’s “Fly Away” in 1998.
This computer-based procedure, analogous to measuring finches’ beaks over time, enabled the researchers to determine the “evolutionary trajectories,” or rate of change, of the four cultural populations. The paper concludes that these trajectories were comparable to those of the four organic populations they looked at, which were “some of the most famous long-term studies of animal evolution in the wild.”