In social heredity the transmission is not determined by consanguinity, and therefore extends to members of alien races when they are incorporated in the social organization.

While the transmission of biological inheritance to each offspring is inevitable and complete, that of social inheritance is largely voluntary.  It is also more or less complete, according to the knowledge, purpose, and effort of the individuals concerned.  The transmission of acquired social and psychic characteristics even from parents to offspring depends on their association, and the imposition on their offspring by parents of their own modes of life.  Sharing with parents their bodily activities, their language and their environment, both social and psychical, the offspring necessarily develop psychic and social characteristics similar to those of the parents.

Evolution takes place through the transformation of inheritance.  The evolution of innate physiological, anatomical, and psychical characters takes place through the transformation of biological inheritance; and the evolution of society and of acquired characters chiefly through the transformation of social inheritance.

Nearly all biologists admit that change in the form of natural selection is one of the principles transforming biological inheritance; but whether the acquired characters of parents are even in the least degree inherited by the offspring, thus becoming innate characters, is one of the important biological problems of recent years.  Into this problem we have not entered, though we recognize that it must have important bearings on sociological science.  Briefly stated, it is this:  Do social and psychic characteristics, acquired by individuals or by groups of individuals, affect the intrinsic inherited and transmissible psychic nature in such ways that offspring, by the mere fact of being offspring, necessarily manifest those characteristics, regardless of the particular social environment in which they may be reared?  Into this problem, thus broadly stated, we do not enter.  Limiting our view to those advanced races which manifest practically equal physiological development, we ask whether or not their differentiating psychic characteristics are due to modifications of their inherited and intrinsic psychic nature, such that those characteristics are necessarily transmitted to offspring through intrinsic biological heredity.  Current popular and scientific sociology seems to give an affirmative answer to this question.  The reply of this work emphasizes the negative.  Although it is not maintained that there is absolutely no difference whatever in the psychic nature of the different races, or that the psychic differences distinguishing the races are entirely transmitted by social heredity, it is maintained that this is very largely the case—­far more largely than is usually perceived or admitted.  Such inherent differences, if they exist, are so vague and intangible as practically to defy discovery and clear statement, and may be practically ignored.