A section of cave bear bone was found in an archeological dig of a Neanderthal campsite that has in it four holes which line up quite closely to the holes that would be needed to make a diatonic scale for a flute. This has lead many to proclaim this the earliest know musical instrument, including its discoverer, Dr. Ivan Turk. There is some doubt of whether this bone fragment was actually a flute, but it would be impossible to ever truly know. A musicologist named Bob Fink uses this flute as evidence to his thesis that there is a natural foundation to the diatonic scale.
Though it would be the earliest if confirmed, there are a number of other flute-like instruments from that era of humanity which have been confirmed, including 9000 year old flutes discovered in China that are still playable, and other bone flutes from France which are about 32,000 years old.
This points to a very interesting conclusion about the human urge to create music. Noam Chomsky solidified the idea that language is inate to humans. That idea is being extended to music, which is similar to language in many ways, but also occupies distinct ares of the brain. Now consider that drums probably would have existed long before this flute, since they are easier to make and simpler in concept. It seems likely that music developed alongside language in our species.