work to confirm this principle and lend it the support of facts. When
we look to its CAUSAL significance, perhaps it would be better to
formulate the biogenetic law thus: "The evolution of the species and
the stem (phylon) shows us, in the physiological functions of heredity
and adaptation, the conditioning causes on which the evolution of the
individual depends"; or, more briefly: "Phylogenesis is the mechanical
cause of ontogenesis."

But before we examine the great achievement by which Darwin revealed
the causes of evolution to us, we must glance at the efforts of
earlier scientists to attain this object. Our historical inquiry into
these will be even shorter than that into the work done in the field
of ontogeny. We have very few names to consider here. At the head of
them we find the great French naturalist, Jean Lamarck, who first
established evolution as a scientific theory in 1809. Even before his
time, however, the chief philosopher, Kant, and the chief poet,
Goethe, of Germany had occupied themselves with the subject. But their
efforts passed almost without recognition in the eighteenth century. A
"philosophy of nature" did not arise until the beginning of the
nineteenth century. In the whole of the time before this no one had
ventured to raise seriously the question of the origin of species,
which is the culminating point of phylogeny. On all sides it was
regarded as an insoluble enigma.

The whole science of the evolution of man and the other animals is
intimately connected with the question of the nature of species, or
with the problem of the origin of the various animals which we group
together under the name of species. Thus the definition of the species
becomes important. It is well known that this definition was given by
Linne, who, in his famous Systema Naturae (1735), was the first to