| Generation | Theoretical Number | Actual Number | |
|---|---|---|---|
| I | 2 | 2 | |
| II | 4 | 4 | |
| III | 8 | 8 | |
| IV | 16 | 14 | |
| V | 32 | 24 | |
| VI | 64 | 44 | |
| VII | 128 | 74 | |
| VIII | 256 | 116[[2]] | |
| IX | 512 | 177[[2]] | |
| X | 1024 | 256[[2]] | |
| XI | 2048 | 342[[2]] | |
| XII | 4096 | 533[[2]] |
A series of forty royal families gives the following averages:—
| Generation | Average Number | |
|---|---|---|
| I | 2.00 | |
| II | 4.00 | |
| III | 7.75 | |
| IV | 13.88 | |
| V | 23.70 | |
| VI | 40.53 |
When we compare these conditions in the thickly populated parts of modern Europe and of America, with their unstable population, with the conditions among primitive tribes, it becomes at once apparent that the total number of ancestors of each type in small communities must be much less than the number of ancestors in the modern states just referred to. A characteristic example is presented by the Eskimo of Smith Sound in North Greenland. From all we know, it seems extremely unlikely that this community ever consisted of more than a few hundred individuals. From what we know about the history of Eskimo communities, we might much rather assume that originally it consisted of a very few families only. The community has been cut off from the outer world for very long periods; and while there may have been accessions of new individuals from outside once each century, on the whole it has remained completely isolated. It is therefore obvious that the ancestry of this group cannot contain anything like the million of people required by the theory, but that all the individuals must be interrelated through their remote ancestry.
Considering, now, the laws of inheritance as outlined before, it would appear that in a community of this type, the members of which number little more than two hundred individuals, the ancestor of every single individual from the eighth generation back must have been the same, because the eighth generation would require theoretically two hundred and fifty-six individuals,—a greater number than are actually found in the community; and the occurrence of any individuals who have not a good many near and remote ancestors in common with the whole rest of the community is highly improbable, if not impossible.
It follows from this at once that the variability of the whole series around its typical average must be rather small, because all the members of the group will have a certain amount of family resemblance. This uniformity of type will, of course, be the greater, the more uniform the ancestral group.
On the other hand, these conditions bring about another peculiar characteristic of the isolated group. Owing to the constant recurrence of the same ancestral types among the whole group, the type of the whole people becomes very similar to the characteristic traits of the small ancestral group; and the smaller this group, the stronger will be the probability of the type of the local group being quite distinct from the type of the whole people to which they belong.
It seems to my mind that these conditions explain to a considerable extent the occurrence of distinct local types in primitive races. When we find, for instance, that in North America a very marked type belongs to the Arctic coast of the continent, that a quite distinct type is found in the Mackenzie basin, still others in well-defined localities on the Pacific coast, again others in the Mississippi basin, one in the southeast, and one along the Rio Grande and in Mexico,—it seems plausible to ascribe their origin to the increase of small isolated groups, which, as we have seen, must necessarily lead to differentiation of type.
This view of the origin of local races is quite in accord with the remarkable results obtained by Johannsen in his studies of heredity. He repeated artificially the conditions which prevail in a small community, and exaggerated them by selecting types of equal form, and by propagating them by self-fertilization. He raised in this way bean-plants from beans of equal weight, and was able to restrict variation of the type, so that practically any kind of bean of particular weight and particular form could be bred true to the type of its ancestor, and without perpetuating the accidental variations of the ancestors. In cases where the ancestry goes back to a limited number of individuals, as among our isolated tribes, the variation will, of course, not be restricted to the same extent; but the characteristic development of a stable type is quite analogous to the experiment made by Johannsen.
Another phenomenon may be pointed out here which is still little investigated, but which deserves careful attention. We have seen that in stable communities in sparsely settled countries the relationship between members of a tribe will be quite close, and that this relationship will necessarily affect the type and its variability. In course of time two areas whose population has thus developed may be thrown into contact, and numerous intermarriages may occur. It will be seen at once, that, although the differences between the two types may be apparently only slight, a complete disturbance in the forms of heredity will result, because a great number of individuals of distinct ancestry are thrown together. To give an example. The South Italians and the Spaniards represent two types not very distinct in physical features, but separated for centuries. The small village communities of Italy, as well as those of Spain, have all the characteristics of communities in which endogamic marriages have been continued for a long period. In the Argentine Republic these two types come into contact and intermarry frequently. We have no observations on the result of this mixture upon physical characteristics, but it has been noted that the distribution of male and female births is quite different from that prevailing in families in which both parents are either Spanish or Italian (Pearl). It is also conceivable that this may be one of the elements bringing about the change of type of urban populations when compared to rural populations in Europe, and that it may have been active in the change of type observed among the descendants of European immigrants in America; for, although the observations have been made on pure types, in America cases of intermarriages of natives of different villages are much more common than in Europe.