Music and language are not single faculties. Each is a collection of smaller mental processes, some shared and some not. Comparing two such abilities side by side shows which parts they share and which they don't, and so reveals how the mind builds rich communication out of simpler building blocks.
Music usually organizes time around a regular, repeating pulse. Speech rhythm has no such pulse; it is a by-product of how stress, syllables and grouping interact. The mind can still organize timing patterns without a beat, and once you look at that non-periodic timing, a language's speech rhythms turn out to leave their mark on the music of the same culture.
Learning the sound system of your native language or music builds a mental grid of sound categories, and that grid then filters everything you hear. These categories are far fewer than the ear could tell apart: scales use only a handful of tones per octave even though people can distinguish many more. The narrowing comes from learning, not from the limits of hearing.
The brain may keep the rules of grammar and the rules of musical harmony in separate networks. The resources that pull those stored rules into play and fit each new element into a growing structure may still be shared between the two. So the two skills can look independent when damaged in one way and interfere with each other when both are working hard at once.
A behavior found in every culture is not automatically a product of natural selection. Language shows strong signs of having been shaped by evolution, while music may be a human invention, like fire, that spread everywhere because it transforms life and even rewires the brain. The best test is whether a capacity like moving to a steady beat exists without being taught.