Overview of the research
The highland from the north part of Yunnan through the west side of Sichuan, extending to the Qinghai–Tibet Plateau in northwest China where the average of altitude is over 3,000 meters above sea level, forms the eastern edge of the Himalayan Plateau. The upper streams of great rivers such as the Mekong, Huanghe, and Changjiang flow through the steep mountainous district, where Tibetans and many ethnic sub-groups live in the valleys and halfway up the mountains. The rivers flow from north to south in this district, and many roads run along the streams through the valleys; they have long been routes for ethnic migration and social exchange between agricultural people and nomadic people. These routes are referred to as “the ethnic corridor of Southwest China,” and dozens of minor Tibeto-Burman languages are spoken there. These languages are so different that their speakers cannot understand each other, even though they have common typological features in their phonology, lexicon, and syntax, and share many cognates. Scholars recognize that these languages are related to one another because they have transmitted more than a few features of the old Tibeto-Burman languages until the present. In this study I describe the features of the modern Sino-Tibetan languages and dialects used in the ethnic corridor, and analyze their structure and grammatical functions based on field research. I also have been conducting a series of studies that included comparative research on the modern dialects, searching for correspondences between modern dialects and historical records and trying to reconstruct their earlier stages to trace the process of historical development. The goal is to investigate the mechanism of development of the typological structures among the languages in the ethnic corridor based on their cognates and shared innovations, and the structural correspondences of their grammatical constructions.