of habits and environment, of use and
disuse, to account for the origin of the appendages, while we attributed
the origin of the metamorphoses of insects to change of habits or of the
temperature of the seasons and of climates, particularly the change in
the earth's climates from the earlier ages of the globe, "when the
temperature of the earth was nearly the same the world over, to the
times of the present distribution of heat and cold in zones."

From further studies on cave animals, published in 1877,[220] we wrote
as follows:

"In the production of these cave species, the exceptional phenomena
of darkness, want of sufficient food, and unvarying temperature,
have been plainly enough _verae causae_. To say that the principle of
natural selection accounts for the change of structure is no
explanation of the phenomena; the phrase has to the mind of the
writer no meaning in connection with the production of these cave
forms, and has as little meaning in accounting for the origination
of species and genera in general. Darwin's phrase 'natural
selection,' or Herbert Spencer's term 'survival of the fittest,'
expresses simply the final result, while the process of the
origination of the new forms which have survived, or been selected
by nature, is to be explained by the action of the physical
environments of the animals coupled with inheritance-force. It has
always appeared to the writer that the phrases quoted above have
been misused to state the cause, when they simply express the result
of the action of a chain of causes which we may, with Herbert
Spencer, call the 'environment' of the organism undergoing
modification; and thus a form of Lamarckianism, greatly modified by
recent scientific discoveries, seems to meet most of the
difficulties which arise in accounting for the origination of
species and higher groups of organisms. Certainly 'natural
selection' or the 'survival of the fittest' is not a _vera causa_,
though the 'struggle for existence' may show us the causes which
have led to the _preservation_ of species, while changes in the
environment of the organism may satisfactorily account for the
original tendency to variation assumed by Mr. Darwin as the
starting-point where natural selection begins to act."

In our work on _The Cave Animals of North America_,[221] after stating
that Darwin in his _Origin of Species_ attributed the loss of eyes
"wholly to disu