The ubiquity of musical behavior in several phylogenetically distinct taxa in the animal kingdom and throughout every society in the human species is one of the greatest unsolved mysteries in biology. I have incorporated knowledge of human musical universals into a measurable working (rhythm absent) definition of melody: essentially variation and repetition of (tonal) intervals. I hypothesized that repetition and variation in melody have evolved as honest signals of underlying quality of precision and range (respectively) of distance gauging abilities. I predicted that melodic display would be positively correlated with remote targeting behaviors such as projectile locomotion (jumping, brachiation, or arm-swinging). Quantitative locomotor distributions and spectrographic vocal repertoires of primates were collected and my spectrogram analysis R-package, [melody], was used to split, match, and score each vocalization type. Four linear least squares regression models of (percent) projectile locomotion vs melodic score (as measured by the number of repeated interval groups per vocalization) were run: on both species level data and the corresponding phylogenetically controlled independent contrasts with and without control from additional behavioral and environmental variables. Percent projectile locomotion was statistically significant at the .01 level but failed to explain more than 20% of the variance in melodic display. This work is an important first step in both investigating possible selection pressures in a currently neglected corner music origins research and, more generally, quantifying the formerly qualitative task of assessing musicality.
