Stewart Brand's HOW BUILDINGS LEARN:  WHAT HAPPENS AFTER THEY'RE BUILT
includes a chapter entitled VERNACULAR:  HOW BUILDINGS LEARN FROM EACH
OTHER.  In it, Brand refers to vernacular building design as evolutionary,
and says:

"In terms of architecture, vernacular buildings are seen as the opposite of
whatever is 'academic,' 'high style,' 'polite.'  Vernacular is everything
not designed by professional architects -- in other words, most of the
world's buildings, ranging in assigned value from now-precious Cotswold
stone cottages and treasured old Cape Cods to the despised hordes of
factory-built mobile homes.  In the eyes of tastemakers, old vernacular is
lovely.  New vernacular...is unlovely."

"The heart of vernacular design is about form, not style.  Style is time's
fool.  Form is times' student." (132)

Tons have been written on vernacular architecture, alot of it in the field
of material culture studies (Henry Glassie's a standard).   Try the library,
Chris.

PS  I really enjoyed this book.

Maura