aring for the one above.
Thus all nature, and especially the realm of life, implies a ladder of
"evolution." What is "potentially" inherent in the lowest form of life has
in the highest, as in man, become actual or "realised" through a
continuous sequence of phases, successively more and more evolved. This
view in its earlier forms was very far from implying that each higher step
was literally "descended" from the one below it, through the physical and
mental transformation of some of its representatives. As the world, in
Aristotle's view for instance, had existed from all eternity, so also had
the stages and forms of life, each giving rise again to its like. Indeed,
the essential idea was that each higher step is simply a development, a
fuller unfolding of the lower stage, and finally that man was the complete
realisation of what was potentially inherent in the lowest of all.

This doctrine of evolution was in modern times the fundamental idea of
Leibnitz and Kant, of Goethe, Schelling and Hegel. It brought unity and
connectedness into the system of nature, united everything by steps,
denied the existence of gaping chasms, and proclaimed the solidarity of
all the forms of life. But to all this the idea of actual descent was
unnecessary. An actual material variation and transition from one stage to
another seemed to it a wooden and gross expression of the evolution idea,
an "all too childish and nebulous hypothesis" (Hegel).

All the important results of comparative morphology and physiology, which
the modern supporters of the doctrine of descent so confidently utilise as
arguments in its favour, would have been welcomed by those who held the
original and general evolution idea, as a corroboration of their own
standpoint. And as a matter of fact they all afford conclusive proofs of
_evolution_; but not one of them, including even the fundamental
biogenetic law and the inoculated chimpanzee, is decisive in regard to
_descent_. This contention is sufficiently important to claim our
attention for a little. Let us take the last example. Transfusion of blood
between two species is possible, not necessarily because they are
descended from one another or from a common root, but solely because of
their systematic (ideal) relationship, that is to say because they are
sufficiently near to one another and like one another in their
physiological qualities and functions. If, assuming descent, this homology
were disturbed, and the sy