CHARLES DARWIN—WEISMANN. 451 
nucleus. I do not mean to say that ali these were the direct result 
of the idea of evolution, but they have an indirect connection with it. 
Anthropology gained quite a new interest after it was recognized 
that man, too, was a product of evolution. A vast number of prob- 
lems presented themselves; it was necessary to investigate the gradual 
becoming not only of the body but of the mind, the evolution of 
the Psyche and all that flows from it. Before that time there had 
been a history of language, of law, of religion, of art, and so on, 
but 1t now became necessary to carry these further back—beyond 
Adam and Eve to the animal ancestors. Undoubtedly a study of 
the psychology of animals is one of the essential tasks of the future! 
I can here only give a few hints without elaborating them, but I 
must emphasize the fact that the idea of evolution, in the form in 
which Darwin presented it to us, has given an impulse to new life 
and further development in every department of human knowledge 
and thought; everywhere it acts as the yeast in cider—it sets up 
fermentation. This has already borne rich fruit, and we may hope 
for much more in the future. 
Our greatest gain from the theory of evolution has, however, been 
the evidence it affords of the unity of nature, the knowledge that the 
organic world must be referred back to the same great everlasting 
laws which govern the inorganic world and determine its course. 
Even if formal proof of this be still wanting, the probability is now 
so strong that we can no longer doubt it. 
It is not only the theory of evolution as a whole, but the active 
principle in it, the principle of selection, that is transforming and 
illuminating all our old conceptions. It is teaching us to understand 
the struggle, silent or clamant, among human races, their rivalry for 
the possession of the earth, and to understand, too, the composition 
of human society, the unconsicious division of labor among the 
members, and the formation of associations. The development of 
“classes” and their union in a State appears in a new light when 
looked at from this point of view. In this department a good deal 
has been already accomplished. 
The study of human health must be particularly influenced by the 
theory of evolution, and a beginning has already been made in this 
department also. 
But there is another and very important point in regard to which 
the theory, of selection must be our guide. If we take a survey of 
the evolution of the world of life as we know it, we see that, on the 
whole, it has been an ascending evolution, beginning with the lowest 
organisms and advancing through higher and higher to the highest 
of all, man himself. It must be admitted that at certain stages in 
this evolutionary series we find retrograde steps (as, for instance, 
