The Tea and Horse Caravan Trail

Tibetans drinking tea earlier than the Chinese?  Importing that tea from southern Yunnan along mule trails cut into the Hengduan Mountains? There is a history extending back for the birth of Christ about the trade of tea in Tibet.  My father-in-law's profession trading tea and horses has a long history indeed, only recently discussed and as poorly understood as the lives of the people (whose nationalities have not even been categorized yet).