with the _absolute_ certainty
of the general theory of descent. It is now ten years since I first
explicitly stated (in my "Natural History of Creation," vol. ii. p.
358): "The pedigree of the human race, like that of every animal or
plant, remains in detail a more or less approximate general
hypothesis. This, however, in no way affects the application of the
theory of descent to man. In this, as in all researches into the
derivation of our organism, we must distinguish between the _general
theory_ of descent and the _specific hypothesis_ of descent. The
general theory of descent claims full and permanent value, because it
is inductively based on the whole range of common biological phenomena
and on their internal causal connection. Each special hypothesis of
descent, on the other hand, is conditional as to its specific value on
the existing state of our biological information, and on the extent of
those objective empirical grounds on which we deductively found the
hypothesis, by our subjective inferences." And I must here
emphatically add that I have on every opportunity repeated that
reservation, and have always insisted on the difference which exists
between the absolute certainty of transmutation in general and the
relative certainty of each individual specific pedigree. So that when
Semper and others of my opponents assert that I teach my specific
genealogies as "infallible dogmas," it is simply false. I have, on the
contrary, pointed out on all occasions that I regard them only as
_heuristic or provisional hypotheses_, and as a means of investigating
the actual relations of cognate races of organic forms more and more
approximately.

Since the conception of the natural animal system as a hypothetical
genealogical tree, and the phylogenetic interpretation of
morphological affinity which that conception involves, afford in fact
the only rational interpretation of that affinity in general, my first
genealogical attempts soon found many imitators, and at the present
time numerous industrious labourers in the different departments of
systematic zoology are endeavouring to find in the construction of
such hypothetical genealogies the shortest and completest expression
of the modern conception of structural affinity. If Virchow had not
been as ignorant of the true significance and method of systematic
morphology as he is of its progress and scientific contents, he must
certainly have known this, and then he would surel