This is just my theory, but I'm sure that it is true. It just makes so much sense to me.
In early Christian churches, all the singers were usually guys.
Why?
Because early Christian music sounds especially great sung in a specific way- unstrained and pure, in a register that is away from the middle of your ear's natural range, so that it sounds otherworldy, but in the unstrained middle of the voice's natural range so that it is unstrained and pure.
For this you need a voice whose natural unstrained middle is away from the ear's natural middle range. Two types of people have such a voice: men, whose unstrained middle range is way down in the baritone range, and children, whose unstrained middle is way up in the mezzo range. Women, on the other hand, have voices whose natural unstrained middle is exactly where the ear's natural middle range is. Women cannot sing in that way.
The old master choir directors knew all about these kinds of subtle affects of vocal range. They were very good at what they did. They were, after all, masters with centuries of experience to learn from.
Thus, outside of nunneries, all the adult church choir singers in the old days were men, simply because a male baritone voice is so beautifully suited to that kind of singing.
And so is a child's voice.
And the children's choirs were training the next generation of adult singers. So the children's choirs were boy's choirs, so that they could train the next generation of adult singers- the next generation of male baritone singers.
And that's why we have boy's choirs. Because men's voices and children's voices are so beautifully suited to traditional Christian music, and the children's chiors were training the next generation of adult singers.
Have fun and know that God loves you!
Sincerely,
David S. Annderson
P.S. I just came from a YouTube video by an incredible boy's choir named Liberia (after the Liberia Me section of the Requiem Mass) singing Carol of the Bells. Such incredible discipline and prescision! It is incredible that such discipline and prescision is found in a children's choir! You can do anything you want if you put your mind to it- if God wants you to!