I can't imagine myself being a-rhythmic. Music necessarily has a pulse like speech and the placement of accents tends to fall into repeated patterns. Not only is rhythm often the most compelling part of music, but quite often that's all there is. It would seem that rhythmic music taps directly into the system of motor control. I believe that performance is an important part of any search for meaning in music.
Music is something that is produced to be heard and responded to.
A virtuoso performance can be seductive, intimidating, or applauded by a significant and influential portion of the community, thus giving the wood thrush mating opportunities, the redwing territorial control, or the pop star social status - which comes back around to mating opportunities, particularly opportunities with the potential of good genetic outcomes. Darwin felt that human music grew out of our ancestor's mating calls. That would suggest that music actually was an adaptation and therefor evolved qua music. Steven Pinker doesn't think so. He sees no Darwinian goals such as long life, grandchildren, or increased ability to predict or understand the world.