e
St. Hilaire and Lamarckian schools, as containing the more
fundamental causes of variation, and adds those of geographical
isolation or segregation (Wagner and Gulick), the effects of
gravity, the effects of currents of air and of water, of fixed or
sedentary as opposed to active modes of life, the results of strains
and impacts (Ryder, Cope, and Osborn), the principle of change of
function as inducing the formation of new structures (Dohrn), the
effects of parasitism, commensalism, and of symbiosis--in short, the
biological environment; together with geological extinction, natural
and sexual selection, and hybridity.

"It is to be observed that the Neolamarckian in relying mainly on
these factors does not overlook the value of natural selection as a
guiding principle, and which began to act as soon as the world
became stocked with the initial forms of life, but he simply seeks
to assign this principle to its proper position in the hierarchy of
factors.

"Natural selection, as the writer from the first has insisted, is
not a _vera causa_, an initial or impelling cause in the origination
of new species and genera. It does not start the ball in motion; it
only, so to speak, guides its movements down this or that incline.
It is the expression, like that of "the survival of the fittest" of
Herbert Spencer, of the results of the combined operation of the
more fundamental factors. In certain cases we cannot see any room
for its action; in some others we cannot at present explain the
origin of species in any other way. Its action increased in
proportion as the world became more and more crowded with diverse
forms, and when the struggle for existence had become more unceasing
and intense. It certainly cannot account for the origination of the
different branches, classes, or orders of organized beings. It in
the main simply corresponds to artificial selection; in the latter
case, man selects forms already produced by domestication, the
latter affording sports and varieties due to change in the
surroundings, that is, soil, climate, food, and other physical
features, as well as education.

"In the case also of heredity, which began to operate as soon as the
earliest life forms appeared, we have at the outset to invoke the
principle of the heredity of characters acquired during the lifetime
of lowest organisms.

"Finally, it is noticeable that whe