An updated version of my paper about the evolution of progressive aspect in Central Zapotec languages has just been posted on my page at Academic.edu.
My essential argument is that progressive aspect marking with ca- is innovation in Central Zapotec, and you can still see the early stages of this in Colonial Valley Zapotec. In the 16th century texts, ca- isn't yet an obligatory marker of progressive (as it is in modern languages in this group).
The Central Zapotec languages include the ones shown in this tree (some branches omitted for visibility), using the classification of Thom Smith Stark (2007):
My essential argument is that progressive aspect marking with ca- is innovation in Central Zapotec, and you can still see the early stages of this in Colonial Valley Zapotec. In the 16th century texts, ca- isn't yet an obligatory marker of progressive (as it is in modern languages in this group).
The Central Zapotec languages include the ones shown in this tree (some branches omitted for visibility), using the classification of Thom Smith Stark (2007):