188 THE THEORY OF THE LIVING ORGANISM

one of the alternative or supplementary theories of evolution which
have been put forward—for instance, Lamarckian inheritance,
or some directing agency guiding the course of evolution to a distant
goal. There may well be some factor operating in evolution no
more suspected at present than in pre-Newtonian days gravitation
was suspected as providing an explanation of the paths of the
planets.

4. Lamarckian inheritance

It must be with some distaste that a biologist approaches the
controversy over the Lamarckian factor in evolution, the 'inherit-
ance of acquired characters/ Some discussion of it is necessary
however, since, in disagreement with the views here maintained,
many biologists, psychologists and philosophers who have adopted
a psychobiological interpretation of vital processes have regarded
it as affording a basis for Lamarckian inheritance and so providing
a rational explanation of evolution; the dynamic factor in evolution
is conceived by them as inherited experience.

The history of this controversy during the last fifty years is
not one of which biologists can be proud. Histories of biological
science written a century hence will surely depict it as a discredit-
able episode in the development of the science. Confused reasoning,
misunderstanding of the problem involved, and bad experimenta-
tion, have all contributed to this situation. The term 'acquired
characters' has itself added to the confusion. As has often been
pointed out, this phrase is meaningless except in the special and
arbitrary sense in which it is used in this connection. We cannot
study the inheritance of 'characters/ but only of <li(Terences of
characters. Substituting the word 'difference/ the phrase 'acquired
differences' is inoffensive if it is understood that 'acquired' means
acquired during the lifetime of the organism. An acquired di iTcrenee
is a difference between two phenotypes of identical genotype; the
zygotes started with identical potentialities of development, but the
phenotypes are different owing to these potentialities having been
actualized in different environments. An innate, as contrasted with
an acquired, difference is a difference due to different constitution
of the zygotes; that is to say, of genotype. According to the
Lamarckian theory, acquired differences become transformed into
innate differences. The use of the expression 'acquired characters*
has, however, become so ingrained in biological literature that we