662 The American Naturalist. [August, 
acquired by the individual are hereditary. This, then, is La- 
marckism—that the controlling factor or process in evolution 
is functional, and that acquired characters are readily trans- 
missible. It is important that I still repeat Lamarck’s belief 
in the transmission of a character obtained by any individual 
during its own lifetime, for this is the starting point of the 
definition of an “ acquired character” concerning the heredi- 
tability of which the scientific world is now rent. “All that 
nature has caused individuals to acquire or lose through the 
influence of the circumstances to which their race has been 
fora long time exposed," says Lamarck, * it preserves," etc. 
And again, “ Every change acquired in an organ by a ħabi- 
tual exercise sufficient to have brought it about, is preserved 
thereafter through heredity,” etc. We shall presently observe 
how far this definition of an acquired character has been main- 
tained by recent philosophers. 
Just fifty years after the publication of Lamarck's theory, 
Darwin proposed a hypothesis which has had a greater influ- 
ence upon the habit of scientific thought than any enunciation 
since the promulgation of inductive philosophy. Darwin, like 
Lamarck, saw that all forms of life vary; and like him, too, 
he perceived that there must be a fierce struggle for place or 
existence amongst the individuals of the rapidly succeeding 
generations. This variation and struggle are particularly 
apparent in cultivated plants; and Darwin saw that the gar- 
dener selects the best, and thereby “improves” the breed. “Can 
it, then, be thought improbable,” says Darwin, “seeing that 
variations useful to man have undoubtedly occurred, that 
other variations useful in some way to each being in the great 
and complex battle of life, should occur in the course of many 
successive generations? Ifsuch do occur, can we doubt (remem- 
bering that many more individuals are born than can possibly 
survive) that individuals having any advantage, however slight, 
over others, would have the best chance of surviving and of pro- 
creating their kind?" “This preservation of favorable indi- 
vidual differences and variations, and the destruction of those 
which are injurious, I have called Natural Selection, or the 
Survival of the Fittest.” This, then, is Darwinism—that the 
