Asian archaeology. Comment on "Agriculture facilitated permanent human occupation of the Tibetan Plateau after 3600 B.P. ".

Chen et al. (Reports, 16 January 2015, p. 248) argued that early Tibetan agriculturalists pushed the limits of farming up to 4000 meters above sea level. We contend that this argument is incompatible with the growing requirements of barley. It is necessary to clearly define past crop niches to create better models for the complex history of the occupation of the plateau.