It has been the general assumption that all the oldest New World cultures were direct importations from Asia–more specifically, from Siberia–and that the prototypes for their distinctive features must be sought in this latter area. A number of successive migrations by very different groups have been taken for granted to account for the varied archaeological picture in Palaeo-Indian times, to say nothing of the subsequent linguistic and physical diversity, but any contacts with the Old World on the Neo-Indian horizon have been generally viewed with suspicion. No specific evidence in support of this viewpoint has ever been adduced, it is true, but so long as Siberia remained a terra incognita, it was assumed that the proofs must be there, awaiting only the spade of the excavator. The proposition was argued, as it were, on the grounds of historical necessity.