of genetic history or at least followed in the footsteps of those who
fully grasped the genetic point of view. But their aim has been to
collect and sift evidence, and determine particular facts; com-
paratively few have given serious thought to the lines of research and
the speculations which have been considered in this paper. They
have been reasonably shy of compromising their work by applying
theories which are still much debated and immature. But historio-
graphy cannot permanently evade the questions raised by these
theories. One may venture to say that no historical change or trans-
formation will be fully understood until it is explained how social
environment acted on the individual components of the society (both
immediately and by heredity), and how the individuals reacted upon
their environment. The problem is psychical, but it is analogous to
the main problem of the biologist.

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