People singing together provides an experience that probably dates back to the dawn of humanity itself:
Not only can humans make more sounds, but we also can control how we string them together. And that is because of our amazing and precise breath control. Monkeys can't control their inhale and exhale the way we can -- they can only make short sounds a few seconds long before they have to take another breath.
And the process seems to bind groups of people together - vide sports venues, battlefields, religious gatherings.