THEORY: Where do genders come frm?

OK, I just read the section of Greville Corbett's _Gender_ about the
origin of gender systems, and I thought I'd try to summarize for the
curious.

Verb gender agreement comes from subject/object pronouns which become
obligatory, even when they are redundant with a full noun phrase
subject, and later become reanalyzed as part of the verb.

But where do the subject pronouns distinguishing gender come from?

Well, subject pronouns tend to come from demonstratives.  So they'd
come from demonstratives which distinguish gender.  Demonstratives
which distinguish gender can also turn into explicit gender markers on
nouns, so there's another element of it.

But where do you get demonstratives which distinguish gender?  From
classifier systems.  Classifier systems distinguish different groups
of nouns,and when they spread, they tend to attach themselves to
demonstratives first, which can result in demonstratives which
distinguish gender.

(Another source may be anaphoric pronouns which have specialized forms
used only for animates -- this may spread and result in an
animate/inanimate distinction.)

So classifiers can attach to or replace demonstratives, giving rise to
demonstratives which distinguish gender, and they can also be repeated
within the noun phrase, giving rise to gender agreement within a noun
phrase.

But where do classifiers come from?  That's easy and well established:
nouns.  Specifically nouns which are general and lend themselves to
classification, like "man," "woman," "thing," "animal," and whatnot.
Indeed, some languages allow a noun to classify itself: in addition to
"the woman Mary" you can have phrases like "the woman woman" ("ix ix"
in Jacaltec).

So the ultimate source for gender distinctions is simply nouns, which
I guess is what you'd expect.

It's worth noting that the abovementioned processes can occur
repeatedly, and their effects can be obscured by phonological
attrition of the resulting markers, so that it's rarely simple and
obvious to see where the genders came from.