Christoph von Furer-Haimendorf 
The Apa Tanis and their Neighbours [PDF ebook] 
A primitive society of the Eastern Himalayas

Inhabiting a secluded valley in the Eastern Himalayas, the Apa Tanis remained virtually unknown to the outside world until 1944-45 when the author spent several months in their villages, studying their internal social structure as well as their political and economic relations with neighbouring tribes.
The economy of the Apa Tanis, who knew neither the principle of animal traction nor the wheel, resembled that of certain Neolithic societies, but the methods used in the exploitation of their natural environment were far from primitive, and a developed agriculture enabled a population of some 20, 000 to live in one valley of 20 square miles.
Originally published in 1962.