The two passages discuss recent scientific research on music.
Main Point (Passage A)
Music, it would seem, had little adaptive value of its own, and most likely developed on the coattails of language (lines 25–27).
Passage Map (Passage A)
P1 - A question about music and language is posed. P2 - Music and language are compared. P3 - An answer to the question is offered—music developed on the coattails of language.
Main Point (Passage B)
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 (lines 32–37).
Passage Map (Passage B)
P1 - A hypothesis is offered about the origins of music. P2 - A phenomenon is described. P3 - An explanation of that phenomenon is offered, which supports the hypothesis.