Human songs are not just about mating and only thus of evolutionary interest as related to survival and continuation of our species.
In the exceptionally beautiful BBC documentary series Planet Earth one episode examines humanity and oceans. The camera team followed a Polynesian man in his lonely boat when he was fishing sharks using traditional methods. He wanted to keep alive the ancient art of shark hunting that is rapidly disappearing. To entice the shark he was singing to it.
There is something definitely prehistoric about this song and indeed, it is possible that for ancient man and woman or for a community songs were centrally important in more than one way. We are all familiar with the Indian dance and their songs, some know the monotonous traditional singing of reindeer shepherds in cold tundra nights. These seem to me like something very ancient and SAN people of South Africa also sing (and dance). Archaeologists have discovered an Upper Palaeolithic flute in a cave in Germany somewhere there at the dawn of human civilization.
If I am right, our closest relative in the animal kingdom, Chimpanzee, does not sing.
So while we can appreciate the fact that music tells about the love of God towards His creation and is a wonderful gift to all of us - that is more or less the end of discussion. Let's do music, listen to music, appreciate those who sing to us love songs or encourage us on our marching to the frontier or sing healing our souls with Balm from Gilead!
However, Charles Darwin's point of view - how this fits the fight for survival, change of species, opens up interesting questions. Why we sing? And trying to answer such fundamental question about humanity some people push forward the frontiers of knowledge in scientific manner.
Divine Grace gives us music and we use it to praise Him.
Nature challenges us intellectually as we try to understand how it works and why we are what we are. Why we sing?
Good scientific theory does not necessarily explain everything. But it raises fruitful questions that advance our knowledge. In such discussion, Darwin's famed theory of evolution is probably among the most influential theories ever presented.