When did the word "guys" begin to include people of both sexes? I seem to remember that when I was in high school (1960s) young women would recoil at being referred to as guys, even as a part of a group that included both boys and girls. Nowadays you rarely hear "gals", but "guys" is everywhere (alas!) when referring to men and women of any age.
I remember seeing some discussion of that 10 or 20 years ago. Why don't you try some Google or Books.google searching and limit it to the time frame between 1960 and 2000?
Emmett
I think it's a regionalism. I grew up in Nevada in the 70s and 80s hearing "you guys" used to mean plural you, regardless of gender, but I've seen cases where that causes confusion elsewhere.
I, too, was in high school in the sixties but my experience with guys comes from my elementary school days. In Fort Worth, Texas (born and raised) calling people "guys" was something only "yankees" did. The only people we heard it from were some who moved from the north and they called both sexes "guys" (this is in the fifties). When I visited my cousins in El Paso I discovered that it was common out there to use "guys" for both sexes. This spoiled my belief that it was only something from the north. By the time I was in high school, it was starting to be common in Fort Worth as well.
It makes perfect sense to me, since the male gender is used as the neuter gender as well.
I find it ironic that "guys" is OK for both genders (accepting the male as neuter), but we hear constructions like "chairwoman" or "chairperson." "Chairman" is not a gender-specific noun, so why change it?