I've found what the famous musicologist Henry Paul Lang had to say about gender and the soprano voice, covering the subject of castrati, and the reasons for the use of boy voices in church. It is very interesting and enlightening, but will take me an hour or so to translate (ironically, I'm going to translate to English the Spanish translation of the original in English). May be tomorrow night I come back. (First I'll search the Web, it is possible that the original version is somewhere in the net).
Un abrazo - Andrés