Over the past few hundred years, the English choral tradition had an insoluble problem.
Who should sing the soprano line?
All answers were a compromise.
Most churches used young boy trebles for the soprano line and either just-pre-pubsecent boys or adult male falsettists (counter-tenors) to sing the alto line.
The result was a homogeneous blending of male tones, but there were obvious limitations from having boy trebles - especially in terms of their childish and inexperienced level of musicality, and from the limited power and dynamic range of a boy's voice.
Experiments to solve this problem included castratos ('nuff said), adult male falsettists screeching up to the soprano line (eek!), and using adult women (who were potentially of much greater musicality, power and dynamic range than boys - but who sang with a warbling femininity which spoiled the purity of blend).
Then came the adult female treble: a woman who was trained to sing like a boy - with a pure, minimal vibrato, treble tone.
The first I heard of these creatures was in a mid 1970s recording of Tallis by David Wulstan conducting the Clerkes of Oxenford.
My understanding is that when Oxford and Cambridge colleges began to go co-educational, some the organists such as Wulstan (in English cathedrals the organists also train and conduct the choir) began to train the female undergraduates to sing like boys.
And it worked very well... very well indeed.
If Wulstan was indeed the pioneer - he deserves much greater recognition than he is currently accorded.
The Clerkes of Oxenford seem to have been the pioneers, but the heights were scaled by the likes of the Tallis Scholars (Peter Phillips) and The Sixteen (Harry Christophers) - then came along some adult women treble soloists such as Emma Kirkby - and the process was complete.
The problem was solved.
There is no compromise in the results of the best choirs using adult women trebles.
They achieve perfection in musicality, dynamics, volume - and even in that holy grail: tonal blend.