I. Haeckel and His Opponents

The monistic doctrine of evolution, however, is in complete agreement with the fact of self-observation. If the human soul has evolved itself slowly and step by step along with the organs of the soul out of lower conditions, then it is self-evident that we can explain its development from below scientifically, though we can discover the inner nature of that which emerges from the complex structure of the human brain only from the contemplation of this very nature itself. Had spirit been always present in a form resembling the human, and had it at last created its likeness in man alone, then we ought to be able to deduce the human spirit from the All-spirit; but if man's spirit has arisen as a new formation in the course of natural evolution, then we can understand its origin by following out its line of ancestry; we learn to know the stage at which it has at last arrived when we contemplate that spirit itself.