for such derivation
were forthcoming. Cuvier and von Baer, as we have seen, combated the
current evolution theories on the ground that the evidence was
insufficient, but von Baer at least had no rooted objection to
evolution. In an essay of 1834, entitled _The Most General Law of Nature
in all Development_,[348] von Baer expressed belief in a limited amount of
evolution. In this paper he did not admit that all animals have
developed from one parent form, and he refused to believe that man has
descended from an ape; but, basing his supposition upon the facts of
variability and upon the evidence of palaeontology, he went so far as to
maintain that many species have evolved from parent stocks. In the
absence of conclusive proofs he did not commit himself to a belief in
any extended or comprehensive process of evolution.

Imbued as he was with the idea of development von Baer saw in evolution
a process essentially of the same nature as the development of the
individual. Evolution, like development, was due to a _Bildungskraft_ or
formative force. The ultimate law of all becoming was that "the history
of Nature is nothing but the history of the ever-advancing victory of
spirit over matter" (p. 71). In a later essay (1835) in the same volume
he says that all natural science is nothing but a long commentary on the
single phrase _Es werde!_. (p. 86).

As we shall see, von Baer adopted in later years the same attitude to
Darwinism as he did to the evolution theories in vogue in his youth.

Although in the twenty or thirty years before the publication of the
_Origin of Species_ (1859) no evolution theory of any importance was
published, and although the great majority of biologists believed in the
constancy of species, there were not wanting some who, like von Baer,
had an open mind on the subject, or even believed in the occurrence of
evolutionary processes of small scope. Isidore Geoffroy St Hilaire, the
son of the great Etienne Geoffroy St Hilaire, seems to have held that
species might be formed from varieties. The law which L. Agassiz thought
he could establish,[349] of the parallelism between palaeontological
succession, systematic rank, and embryological development, tended to
help the progress of evolutionary ideas. J. V. Carus, who afterwards
became a supporter of Darwin, seems already, in 1853, to have inferred
from Agassiz's law the probability of evolution.[350]

But no evolution theory was taken very seriously befo