However, one should be careful not to make too hasty generalizations regarding the similar products in different parts of the world, for there is such universality of the traits of the human mind that, with similar stages of advancement and similar environments, man's adaptive power would cause him to do the same thing in very much the same way. Thus, it is possible for two races that have had no contact for a hundred thousand years to develop indigenous products of art which are very similar. To illustrate from a point of contact nearer home, it is possible for a person living in Wisconsin and one in Massachusetts, having the same general environment--physical, educational, ethnic, religious--and having the same general traits of mind, through disconnected lines of differentiation, to write two books very much alike or two magazine articles very much alike. In the question of fundamental human traits subject to the same environmental stimuli, in a general way we expect similar results. With all this differentiation, progress as a whole represents a continuous change from primitive conditions to the present complex life, even though its line of travel leads it through the byways of differentiation. Just as the development of races has been through the process of differentiation from an early parent stock, cultural changes have followed the same law of progressive change. Just as there is a unity of the human race, there is a unity of progress that involves all mankind. _The Study of the Uncultured Races of To-Day_.--It is difficult to determine the beginnings of culture and to trace its slow development. In accomplishing this, there are two main methods of procedure; the first, to find the products or {28} remains of culture left by races now extinct, that is, of nations and peoples that have lived and flourished and passed away, leaving evidence of what they brought to the world; also, by considering what they did with the tools with which they worked, and by determining the conditions under which they lived, a general idea of their state of progress may be obtained. The second method is to determine the state of culture of living races of to-day who have been retarded or whose progress shows a case of arrested development and compare their civilization statistically observed with that of the prehistoric peoples whose state of progress exhibits in a measure similar characteristics to those of the living races.