The former of these two modes of change, substitution, has undoubtedly been effected on a large scale, producing in certain instances radical changes in the racial quality of the populations of some countries; that is to say, there has been more or less gradual substitution of one race for another, while the nation as a geographical and political entity, with its language and much of its laws, institutions, and customs, lives on without complete breach of continuity, and the people, although by blood radically changed, continues to regard itself as the same people, accepting as its own the traditions of those predecessors whom they mistakenly regard as their ancestors. Perhaps the most striking and complete change of this sort in European history was the change of racial character of the Greek people. It is now pretty well established that the Greek population of the classical age was an incomplete blend of two of the three great European stocks, namely _Homo Europaeus_, the northern, fair, long-headed type of tall stature, and of _H. Mediterraneus_, the short dark long-headed type of the Mediterranean coast lands. The Pelasgians, who, as we now know, had achieved a civilisation of a type that was widely spread through southern Europe as long as three thousand years or more before our era, seem to have been of this Mediterranean race. Rather more than a thousand years before our era, the Pelasgian population of Greece and the neighbouring regions began to be overrun and conquered by tribes of the fair Northern race which came in successive invasions, the Thracians, the Hellenes, the Achaeans, the Ionians, and later the Dorians. Just as, at a later period, men of the Northern race established themselves as a military aristocracy over the Celtic peoples of western Europe, so these invading tribes established themselves as a military aristocracy over the populations of Mediterranean race; and, as in the former case, so here, they intermarried largely with the people they conquered and formed an imperfectly blended population, in the upper social strata of which the fair type was predominant, in the lower strata the dark type. From this happy blending of two races was formed the people which, under the favourable geographical and social conditions of that time and place, evolved the civilisation that culminated after six hundred years in the Athenian culture of the time of Pericles. And then, after a very short time, the whole of that splendid civilisation faded away, and the Greek people sank to a position of slight importance from which it has never again risen. After having displayed in several departments of the intellectual life a power and originality such as have never been approached by any other people, they became a people of very mediocre capacities, devoid of power of origination and purely imitative.