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. After we have thus considered the influences of heredity and environment, so far as they determine the characteristics of distinct types of man, it remains to add a few words on the individuals constituting each type, and on the different distribution of individuals in distinct types.