Biology Reference
In-Depth Information
matter. Darwin was also the author of a pangenetic theory pub-
lished in 1868 in his topic
The Variation of Animals and Plants
under Domestication
. This theory did not occupy a central place in
his work, as he was not directly interested in questions of heredity
and ontogenesis, but was, for him, more a question of filling a gap.
The theory of natural selection needed an explanation of the variations
on which selection operated, and therefore of reproduction.
Darwin's position was not as clear cut as that of the synthetic
theory of evolution which has integrated contributions from 20th
century genetics, particularly the existence of random mutations.
His concept seems implicitly to call on a theory involving random
variation which he could never formulate himself due to the stage
of development of knowledge in his time. There is evidence for this
point in the first sentence of chapter V of
The Origin of Species
,
devoted to the laws of variation:
“I have hitherto sometimes spoken as if the variations — so com-
mon and multiform in organic beings under domestication, and in
a lesser degree in those in a state of nature — had been due to
chance. This, of course, is a wholly incorrect expression, but it
serves to acknowledge plainly our ignorance of the cause of each
particular variation”
(OS p. 173).
Darwin did accept as causes of hereditary variation both the
direct influence of the environment and the use and disuse of organs
(OS pp. 173-204). These factors are usually considered to be typi-
cally Lamarckian,
46
including by the most orthodox Darwinians.
The classic example given to illustrate the effect of these factors is
the neck of the giraffe which elongates as it tries to eat leaves at
the top of the tree. The presence of these Lamarckian elements in
Darwin has already been underlined by André Pichot (Noble, 2006;
Pichot, 1993). However, Darwin also thought that in many cases vari-
ability was 'indefinite' and 'fluctuating' (Darwin, 1868). He considered
46
Incorrectly, as Lamarck, like Darwin, only conformed to the generally
accepted opinion on the subject.
