For two million years there had been "human" species, many of them with our unique characteristics like an upright stance, bipedal locomotion, opposable thumbs, and large brains. Anatomically modern humans - our own species, homo sapiens - appeared in Africa around 150,000 years ago. However, there is no evidence that any of these homo species behaved in a distinctly human way.
Then, it seems, something strange happened. Sometime between 75,000 and 25,000 years ago, homo sapiens began to think in a completely different way than any creature that had come before. Not only did humans begin making compound tools, but decorative objects with no practical purpose at all. They began to wear not only animal skins to keep warm, but cosmetic ornaments like beads and necklaces. Ancient caves were decorated with elaborate paintings, they began to bury the dead, and we see at this time the first musical instruments.
This was a difference in kind, and not merely degree. All animals can interact with the environment in a simple stimulus-response pattern. Some very advanced animals can communicate through signal-response, using calls and displays to guide behavior. Neither of these accounts for abstract reasoning or symbolic thinking. Logical reasoning, thinking about meaning, or considering truth and beauty go beyond simply interacting with the environment. (cf. Lost in the Cosmos by Walker Percy, pg. 85-126.) However, it is this type of thinking that is prerequisite for art, language, literature, religion, mathematics, science, and of course, music.