We have seen that they seem to have been of the Nordic type, but this statement needs qualification. We are accustomed to speak of Nordics, Alpines and Mediterraneans, and to describe their physical characters in considerable detail. We are well aware that the population of every country in Europe is mixed, and contains many examples of at least two of these types and a larger number of individuals who resemble one type in this feature and another in that; there are also many who display intermediate characters. But from this mass of heterogeneous material we believe that we have isolated these types, which we consider pure, and we treat the bulk of the population as a mixture of these, varying in its components and their proportions in each region. This postulates that there was a time, the race-making period of some writers,[482] when each of these races was living, pure and unmixed, in some area of isolation. That this position has led to clear thinking and has advanced the science of physical anthropology is undoubted, but we have to consider whether it represents a condition which has actually occurred. That such a pure and homogeneous type would evolve if a community were isolated from all others for a sufficient length of time is probable, but we have no clear evidence that such a state of isolation has been preserved for a sufficient period in any part of Europe, or for that matter in the world. The Andamanese have for long kept themselves in fairly complete isolation in a small group of islands, yet their type seems to show evidence of admixture. The same is more true of the Australian aborigines, although the island continent has almost succeeded in keeping out other placental animals. It is true that as we go back into the past, especially into early neolithic times, the skulls in any given region appear more homogeneous than is the case at later periods. After the forests had appeared in Magdalenian times, and until the metal trade arose, communities seem to have been more isolated than either before or after. This was, apparently, the race-making period postulated by McDougall. But the communities who settled at that time in these regions of isolation were to some extent of mixed ancestry, and their isolation was not of sufficient length to insure absolute homogeneity, though we find a closer approximation to it then than has occurred since.