Similar results in nations and tribes can easily be supplied from the great migrations of the past. The wider movements are but due to comparatively small aggregates of adventurous men, in other words to the aggregation of many similar central nervous systems. The great Western and Southern adventures of the Scythian Tribes had many contributing causes on which the historian has much to say, and they were physically highly efficient for their new career, but, reduced to the simplest elements, it was neither their great stature, strong muscles, flaxen hair, nor blue eyes, but the cerebral constitution of a comparatively small group of them which brought part of the nation to the promised land, and left another and large part in their homes beyond and along the Danube. The subsequent story of the latter may well be compared with the invaders of Gaul and Italy in connection with initiative in evolution. The successive invasion of Britain by Low German tribes in the fifth century, and the Scandinavian hordes of Swedes, Danes, Norwegians, Letts and Finns in the eighth and ninth teach the same lesson. The later condition and development of the Northmen in France, Italy, Spain, Sicily and Britain have only to be compared for a moment with that of their races who remained in Norway, Sweden and Denmark and their descendants, to bring clearly before one’s mind the profound influence exerted by the cerebral constitution of the original Viking hosts on their career in their new environments, and, indeed, on the environments themselves; as in intermarriage with their conquered foes. These examples have been chosen for the reason that one feature is common to them all, the introduction of an individual or group into new environments by reason of the constitution of their brains, irrespective of the contributing factors. If these be sound analogies they bear closely on the matter of initiative in the evolution of new forms of life. The men in question came to their task, in their day, with a certain equipment of brain derived from many ancestors and much nurture. Unconscious arbiters of their fate and that of multitudes who should follow them, they initiated a course of physical and cerebral evolution of which we can see much revealed before our eyes. The motive power of their conduct bears a relation to their physical forms that the engines of a motor-car do to its varied forms of body. The latter are modified indefinitely to suit convenience, comfort and grace, but fundamentally they exist and are energised by the former, just as structure is modified for the performance of function.