north. Speakers from different points within any of the three regions can generally understand one another reasonably well. There are nonetheless significant local-level differences across each. (Wanka Quechua, in particular, has several very distinctive characteristics that make the variety more challenging to understand, even for other Central Quechua speakers.) Speakers from different major regions, particularly Central or Southern Quechua, are not able to communicate effectively. The lack of mutual intelligibility among the dialects is the basic criterion that defines Quechua not as a single language, but as a language family. The complex and progressive nature of how speech varies across the dialect continua makes it nearly impossible to differentiate discrete varieties; Ethnologue lists 45 varieties which are then divided into two groups; Central and Peripheral. Due to the non-intelligibility among the two groups, they are all classified as separate languages. As a reference point, the overall degree of diversity across the family is a little less than that of the Romance or Germanic families, and more of the order of Slavic or Arabic. The greatest diversity is within Central Quechua, or Quechua I, which is believed to lie close to the homeland of the ancestral Proto-Quechua language. Family tree Alfredo Torero devised the traditional classification, the three divisions above, plus a fourth, a northern or Peruvian branch. The latter causes complications in the classification, however, as the northern dialects (Cajamarca–Cañaris, Pacaraos, and Yauyos–Chincha) have features of both Quechua I and Quechua II, and so are difficult to assign to either. Torero classifies them as the following: Quechua I or Quechua B, aka Central Quechua or Waywash, spoken in Peru's central highlands and coast. The most widely spoken varieties are Huaylas, Huaylla Wanca, and Conchucos. Quechua II or Quechua A or Peripheral Quechua or Wanp'una, divided into Yungay (Yunkay) Quechua or Quechua II A, spoken in the northern mountains of Peru; the most widely spoken dialect is Cajamarca. Northern Quechua or Quechua II B, spoken in Ecuador (Kichwa), northern Peru, and Colombia (Inga Kichwa) The most widely spoken varieties in this group are Chimborazo Highland Quichua and Imbabura Highland Quichua. Southern Quechua or Quechua II C, spoken in Bolivia, Chile, southern Peru and Northwest Argentina. The most widely spoken varieties are South Bolivian, Cusco, Ayacucho, and Puno (Collao). Willem Adelaar adheres to the Quechua I / Quechua II (central/peripheral) bifurcation. But, partially following later modifications by Torero, he reassigns part of