The ideas by which the genius of Karl Marx completed in the domain of social economy the revolution effected by science are in number three.

The first is the discovery of the law of surplus-labor.  This law gives us a scientific explanation of the accumulation of private property not created by the labor of the accumulator; as this law has a more peculiarly technical character, we will not lay further stress upon it here, as we have given a general idea of it in the preceding pages.

The two other Marxian theories are more directly related to our observations on scientific socialism, since they undoubtedly furnish us the sure and infallible key to the life of society.

I allude, first, to the idea expressed by Marx, as long ago as 1859, in his Critique de l’economie politique, that the economic phenomena form the foundation and the determining conditions of all other human or social manifestations, and that, consequently, ethics, law and politics are only derivative phenomena determined by the economic factor, in accordance with the conditions of each particular people in every phase of history and under all climatic conditions.

This idea which corresponds to that great biological law which states the dependence of the function on the nature and capacities of the organ and which makes each individual the result of the innate and acquired conditions of his physiological organism, living in a given environment, so that a biological application may be given to the famous saying:  “Tell me what you eat and I will tell you what you are,”—­this sublime idea which unfolds before our eyes the majestic drama of history, no longer as the arbitrary succession of great men on the stage of the social theatre, but rather as the resultant of the economic conditions of each people, this sublime idea, after having been partially applied by Thorold Rogers[78] has been so brilliantly expounded and illustrated by Achille Loria,[79] that I believe it unnecessary to say anything more about it.

One idea, however, still appears to me necessary to complete this Marxian theory, as I remarked in the first edition of my book:  Socialismo e criminalita.

It is necessary, indeed, to rid this impregnable theory of that species of narrow dogmatism with which it is clothed in Marx and still more in Loria.

It is perfectly true that every phenomenon, as well as every institution—­moral, juridical or political—­is simply the result of the economic phenomena and conditions of the transitory physical and historical environment.  But, as a consequence of that law of natural causality which tells us that every effect is always the resultant of numerous concurrent causes and not of one cause alone, and that every effect becomes in its turn a cause of other phenomena, it is necessary to amend and complete the too rigid form that has been given to this true idea.

Just as all the psychical manifestations of the individual are the resultant of the organic conditions (temperament) and of the environment in which he lives, in the same way, all the social manifestations—­moral, juridical or political—­of a people are the resultant of their organic conditions (race) and of the environment, as these are the determining causes of the given economic organization which is the physical basis of life.