The aboriginal peoples of the region thus described fall into a number of groups of exceptional interest to the ethnologist. In the Chaco, to the north, are to be found, to this day, tribes practically untouched by the influence of civilization--tribes in the state which for untold centuries must have been that of the peoples of central South America. Some of them show signs of having been under the influence of the cultured peoples of the Andean regions, preserving in their fabrics, for example, figured designs strikingly like those of Incaic Peru. It has even been suggested that the region is in no small part peopled by descendants of Indians who in former times fled from the west, first before the armies of the Incas, later before the advance of Spanish power.
This constant pressure, which can in a measure be followed in historic times, has had its effect in pushing southward peoples whose origin must be sought in the central region. Such a people are the Abipone--a group of tribes which owe their especial fame among South American Indians perhaps more to the fact that they were so faithfully pictured by Father Dobrizhoffer, during the period in which they were gathered in missions, than to their own qualities, striking as these are. In any case, the Abipone, who in the eighteenth century had become an equestrian people of the open country, had, according to their own tradition, moved southward out of the forests, bearing with them many of the traits still to be found among the tribes of the Chaco.
The Calchaqui civilization, of the Andean region just north of latitude 30º was one of the latest conquests of the Inca power, and represents its southerly extension. The actual dividing line, as recorded by Garcilasso, was the river Rapel, latitude 34º, where, according to the historian, the Inca Tupac Yupanqui was held in his southward advance by the Araucanian (or Aucanian) tribes who formed the population of Chile and west central Argentina. The Araucanians enjoy the proud distinction of being to this day an unconquered people; for they held their own in long and bloody wars with the Spaniards, as before they had held against the aggressive Incas. Further, in their general culture, and in intellectual vigor, they stand at the head of the peoples of southerly South America.