There was another reason also why racial type should be held liable to easy change. The Greeks themselves, and most of their neighbours, were mongrel peoples, for reasons which we have just seen; and there is no doubt that climate and mode of life were actually resulting in ruthless and rapid elimination of intrusive types, wherever these were intolerant of Mediterranean conditions. Now in most of the states of Ionia the blood of the citizens was mixed beyond hope of disentanglement, even by family tradition; for family tradition, as Professor Murray has shown us,[102] was for the most part shattered in the migrations. Yet the external conditions were the same for all; and men saw their blonder kinsmen and townsmen fade and cease out of the land, without fully realizing that what needed explanation was not their failure to survive, but their presence in those latitudes at all. The result, for ethnology, was to encourage a belief that mankind in itself was a pure-bred species, one and indivisible like any other natural kind; and that the marked variations between white and black, straight-haired and woolly-haired peoples, were exclusively the result of climatic, if not human, selection. Yet another consideration drove men’s thoughts inevitably in the same connexion. One of the best inheritances of Greece from the Minoan world was an elaborate apparatus of cultivated plants and animals: our evidence from dogs, and olive-kernels, begins, I think, to justify this view.[103] And in so minutely subdivided a region, special breeds of local origin were bound to result at an early phase of industry; and to be compared and discussed in the markets and on the quays. Every one knew, in fact, that domesticated animals and plants, under human direction, were tolerant of almost infinite and very rapid alteration: and Man himself is the most highly domesticated of all. It is no wonder then that in the fourth century Socrates is represented as arguing habitually as if Man were a domesticated animal, whose breed could be improved at will, and in any direction, physical or psychological. For even psychological breeding had long been reduced to an art, both with horses and with dogs. Demonstrable migrations of men, therefore, and demonstrable mutations both of men and of animals, offered evidence of a kind which it was difficult to overlook, that natural characters were variable, and also that acquired ones could become hereditary. It was, in fact, not because the Greeks knew so little, but because on certain crucial points they already knew so much, that they formed the views they did as to the instability of human varieties. How far these views were pressed to their conclusions will be seen best, I think, from a glance at the teaching of Hippocrates, which we may safely take to be near the highwater-mark of fifth-century thought on immediately pre-Socratic lines.