> but then what's the advantage for women to have a higher pitched voice?

Living in a neighborhood with a lot of teenagers, I will dare a guess; this loud, high pitched scream was probably a very efficient call for help.

But I see your point, and I agree that the answer could be just as simple as randomness of genetics. It just feels rather unsatisfactory for a change who must have taken far more than one single mutation to be that common. Feels like someone winning the lottery a dozen times in a row.