The two passages discuss recent scientific research on music. They are adapted from two different papers presented at a scholarly conference.

Passage A

Did music and human language originate separately or together? Both systems use intonation and rhythm to communicate emotions. Both can be produced vocally or with tools, and people can produce both music and language silently to themselves.

Brain imaging studies suggest that music and language are part of one large, vastly complicated, neurological system for processing sound. In fact, fewer differences than similarities exist between the neurological processing of the two. One could think of the two activities as different radio programs that can be broadcast over the same hardware. One noteworthy difference, though, is that, generally speaking, people are better at language than music. In music, anyone can listen easily enough, but most people do not perform well, and in many cultures composition is left to specialists. In language, by contrast, nearly everyone actively performs and composes.

Given their shared neurological basis, it appears that music and language evolved together as brain size increased over the course of hominid evolution. But the primacy of language over music that we can observe today suggests that language, not music, was the primary function natural selection operated on. Music, it would seem, had little adaptive value of its own, and most likely developed on the coattails of language.

Passage B

Darwin claimed that since "neither the enjoyment nor the capacity of producing musical notes are faculties of the least [practical] use to man . . . they must be ranked amongst the most mysterious with which he is endowed." I suggest that the enjoyment of and the capacity to produce musical notes are faculties of indispensable use to mothers and their infants and that it is in the emotional bonds created by the interaction of mother and child that we can discover the evolutionary origins of human music.

Even excluding lullabies, which parents sing to infants, human mothers and infants under six months of age engage in ritualized, sequential behaviors, involving vocal, facial, and bodily interactions. Using face-to-face mother-infant interactions filmed at 24 frames per second, researchers have shown that mothers and infants jointly construct mutually improvised interactions in which each partner tracks the actions of the other. Such episodes last from one-half second to three seconds and are composed of musical elements—variations in pitch, rhythm, timbre, volume, and tempo.

What evolutionary advantage would such behavior have? In the course of hominid evolution, brain size increased rapidly. Contemporaneously, the increase in bipedality caused the birth canal to narrow. This resulted in hominid infants being born ever-more prematurely, leaving them much more helpless at birth. This helplessness necessitated longer, better maternal care. Under such conditions, the emotional bonds created in the premusical mother-infant interactions we observe in Homo sapiens today—behavior whose neurological basis essentially constitutes the capacity to make and enjoy music—would have conferred considerable evolutionary advantage.