"In this world of a war of all against all, The Naga's added the ritual importance of head-hunting. Life was given it's central purpose by the quest for heads. Boys would not become men without the ritual tattooing only to be undertaken after a successful head-hunt; girls would not be attracted to men without the spendid head-hunting dance and decorations. Success and merit in every field depended on heads."
Extract from: http://www.alanmacfarlane.com/bamboo_naga_front/front.htm