>>After all, with conversation - whether direct or by telephone - we can
usually tell the gender of the speaker by the sound of his/her voice

When I was reading lots of written examinations (hundreds of students) I was trying to guess the sex from the way in which they write (by hand - the keyboard make us more similar).
There were a lot of not predictable sexes - but 2 extremal behaviours: round, ordered, clean, sometimes with small circles (instead of the dot) over the "i" was always female; in the other part, the most confused, hardly readable was always male (like refusing any rule). I was wondering how much this difference was given or forced by education.
Ciao
Emanuela