Lamarck, as is well known, formulated a definite theory of evolution at
the beginning of the nineteenth century, exactly fifty years before
the Darwin-Wallace principle of selection was given to the world.
This brilliant investigator also endeavoured to support his theory by
demonstrating forces which might have brought about the transformations
of the organic world in the course of the ages. In addition to other
factors, he laid special emphasis on the increased or diminished use
of the parts of the body, assuming that the strengthening or weakening
which takes place from this cause during the individual life, could be
handed on to the offspring, and thus intensified and raised to the rank
of a specific character. Darwin also regarded this LAMARCKIAN PRINCIPLE,
as it is now generally called, as a factor in evolution, but he was not
fully convinced of the transmissibility of acquired characters.
As I have here to deal only with the theory of selection, I need not
discuss the Lamarckian hypothesis, but I must express my opinion that
there is room for much doubt as to the cooperation of this principle in
evolution. Not only is it difficult to imagine how the transmission of
functional modifications could take place, but, up to the present time,
notwithstanding the endeavours of many excellent investigators, not
a single actual proof of such inheritance has been brought forward.
Semon's experiments on plants are, according to the botanist Pfeffer,
not to be relied on, and even the recent, beautiful experiments made
by Dr Kammerer on salamanders, cannot, as I hope to show elsewhere,
be regarded as proof, if only because they do not deal at all with
functional modifications, that is, with modifications brought about by
use, and it is to these ALONE that the Lamarckian principle refers.