As to how this came to be, I need to take you on a short tour through the history of popular vocal music.

For a very long time, high singing voices have been associated with heroes, sex symbols, and so forth. This ancient convention is still embodied in grand opera, where the hero is almost always a tenor (1) and the heroine normally a soprano (2). In opera, low voices are generally used for characters who are older--the hero's father, for example, is usually a baritone or a bass; the old wise woman is typically an alto--or for bad guys. Sidekicks are often in the middle voice ranges.

This was still true as late as the 1920s; just listen to the Disney movie Snow White and the Seven Dwarfs. (As the father of an eight-year- old, I do this regularly.) Snow White is a soprano (actually a Betty Boop voice) and her prince is a typical pop-music tenor voice of the time. Popular songs of that time were definitely in the tenor/soprano range--unlike today, when popular sheet music is barely singable by women who lack that rarest of voices, contralto.

Disney movies still follow Broadway, which keeps the high- voice-equals-love-interest equation. See below.

Sopranoes hung on in pop music until probably the 1950s or 1960s, but "low voice = sultry love goddess" was the equation throughout that period--and earlier; it probably dates to Mae West or before--and pop divas started following it by about 1965. Speaking in an alto voice, even if one is a soprano, became de rigeur at the same time, probably earlier.

By now, the pop-music convention is that sexy women have alto voices. Sopranoes are often thought of as ditzy--or innocent, which is for some reason considered the same thing.

This is NOT necessarily true on Broadway. Bernadette Peters is a soprano, as is the great Julie Andrews; and both of them have had stage roles that were neither ditzy nor innocent.

For some reason, this never really caught on for men. Tenor, or at least high baritone ("Broadway baritone"), is still the voice of choice for leading men, especially singing leading men. And this is also true of male pop stars. I can count baritones, who sing in their real voice range AND get into the pop music top forty as solo artists, on the fingers of one hand. Solo pop-music basses don't exist.

So again, male and female pop singers (especially the "boy bands" and "girl bands" put together for mass consumption) sound the same because they sing in the same voice range. The boys sing high, the girls low, and high for a man is low for a woman.

A word about my qualifications: I did one of my undergraduate degrees in vocal performance--and I'm a baritone.

1. In Russian opera, the heroes are typically baritones or basses. I guess Russians don't think tenors are very manly.

2. In some less formal operas like Carmen, the heroine may be a mezzo-soprano--but she is never an alto.