Sino-Tibetan homeland in the Sichuan Basin before 9000 years BP, with an associated taxonomy reflecting various outward migrations over time, first into northeast India, and later north (the predecessors of Chinese and Tibetic) and south (Karen and Lolo–Burmese). Roger Blench argues that agriculture cannot be reconstructed for Proto-Sino-Tibetan. Blench and Mark Post have proposed that the earliest speakers of Sino-Tibetan were not farmers but highly diverse foragers in the eastern foothills of the Himalayas in Northeast India, the area of greatest diversity, around 9000 years BP. They then envisage a series of migrations over the following millennia, with Sinitic representing one of the groups that migrated into China. Zhang et al. (2019) performed a computational phylogenetic analysis of 109 Sino-Tibetan languages to suggest a Sino-Tibetan homeland in northern China near the Yellow River basin. The study further suggests that there was an initial major split between the Sinitic and Tibeto-Burman languages approximately 4,200 to 7,800 years ago (with an average of 5,900 years ago), associated with the Yangshao and/or Majiayao cultures. Sagart et al. (2019) performed another phylogenetic analysis based on different data and methods to arrive at the same conclusions with respect to the homeland and divergence model but proposed an earlier root age of approximately 7,200 years ago, associating its origin with millet farmers of the late Cishan culture and early Yangshao culture. Classification Several low-level branches of the family, particularly Lolo-Burmese, have been securely reconstructed, but in the absence of a secure reconstruction of a Sino-Tibetan proto-language, the higher-level structure of the family remains unclear. Thus, a conservative classification of Sino-Tibetan/Tibeto-Burman would posit several dozen small coordinate families and isolates; attempts at subgrouping are either geographic conveniences or hypotheses for further research. Li (1937) In a survey in the 1937 Chinese Yearbook, Li Fang-Kuei described the family as consisting of four branches: Indo-Chinese (Sino-Tibetan) Chinese Tai (later expanded to Kam–Tai) Miao–Yao (Hmong–Mien) Tibeto-Burman Tai and Miao–Yao were included because they shared isolating typology, tone systems and some vocabulary with Chinese. At the time, tone was considered so fundamental to language that tonal typology could be used as the basis for classification. In the Western scholarly community, these languages are no longer included in Sino-Tibetan, with the similarities attributed to diffusion across the Mainland Southeast Asia linguistic area, especially since . The exclusions of Vietnamese by Kuhn and of Tai and Miao–Yao by Benedict were vindicated in 1954