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LAMARCK, JEAN BAPTISTE PIERRE ANTOINE
DE MONET DE (b. Bazentin-le-Petit, Picardy,
France, 1 August 1744; d. Paris, France, 28 December
1829), botany, invertebrate zoology and paleontology,
evolution.
Lamarck has been credited with introducing a
branching family tree into evolutionary theory. It is
true that in his major evolutionary works he often
spoke of branchings below the level of the “masses,”
but he regarded these branchings as exceptions to the
general rule of increasing structural complexity. In the
Philosophie zoologique, Lamarck argued for a unilinear
series of classes in each kingdom. In an addition at the
end of the work, however, he presented a branching
arrangement for animal classes in what is now a well-known
diagram. It is significant that he was never able
to integrate this new order with his evolutionary
theory. The same discontinuity occurs in the 1815
“Introduction”; in the body of the work he assume a
linear series of the “masses,” and in a supplement he
presents a diagram of branching classes (different
from the 1809 version) which he labels as the presumed
order of formation. These evolutionary trees were
Lamarck's acknowledgment of advances in comparative
anatomy and natural classification. That he could
not include them with his two-factor theory shows his
strong lifelong commitment to a philosophical idea:
the chain of being and its modified version of a
hierarchical unilinear series of classes in the two
kingdoms.
The above example indicates a very important
aspect of Lamarck's evolutionary theories. They were
put forth by a philosopher-naturalist and not a
positivist scientist. From his earliest scientific work,
Lamarck was always more interested in the broad
picture of nature and in general interrelations than in
the details. While he did give scattered examples to
support his theories, he was never systematic, always
promising more evidence in a forthcoming work and
never producing it. Lamarck felt that his theories were
so obvious that they did not need extensive proof.
In addition he was paranoid with respect to the
French scientific community because of their attitudes
toward his work in chemistry; he was convinced that
he never could win over his enemies, so he did not try.
With all his work in botany and invertebrate zoology,
he would have had abundant examples if he had
wanted them. He always separated his theories and
his detailed classificatory work. Although he spent
years carefully determining, describing, and classifying
species, in his evolutionary views he maintained that
species were almost irrelevant, exceptions to the
general natural law of evolution.
Origins of Lamarck's Theory.
Lamarck was fifty-five
when, in 1800, he made his first public statement
of evolution. Until the late 1790's he had believed in
the fixity of species. Thus the question has always
been why he changed his mind. Various answers have
been and still are being put forth. They range from
different influences from his own work to the particular
influence of individuals. Among the former
explanations, Lamarck's work in geology, invertebrate
classification, paleontology and the problem of
extinction, and chemistry have all been seen as the
crucial factor. Individuals who have been held to have
exerted the decisive influence on Lamarck's change
of mind include Lacépède, Cabanis, Cuvier, and such
earlier speculative thinkers as Buffon, Diderot, De
Maillet, and Robinet. A study of the origins of
Lamarck's theory of evolution must be broadened
beyond the issue of the fixity of species. He also
changed his views on other issues. Not only should we
look at the changes, but we should also look at the
continuities. Many aspects of Lamarck's evolutionary
theory are found in his earlier works in different fields;
some components of the theory, however, are new.
Burkhardt, who recognizes the importance of continuities,
has recently studied certain factors which he
thinks were the immediate causes of Lamarck's
evolutionary thought. In an article (1972) he presents
a convincing argument to show that Lamarck changed
his views on two important subjects (spontaneous
generation and the mutability of species) between the
spring of 1799 and the spring of 1800 and that in
both cases the changes came about as a result of
confronting the question of extinction. In the section
on invertebrate paleontology, we summarized
Burkhardt's position. Lamarck was faced with the
extinction question in his study of fossil shells. Since
an acceptance of extinction would have violated his
view of nature, and since the migration theory was not
really a satisfactory explanation, Lamarck was left with
the choice that species change gradually with time.
Lamarck's acceptance of the possibility of spontaneous
generation came via a more circuitous route
but one which was also related to the study of invertebrates
and to the extinction question. Burkhardt
suggests that Lamarck's study of the invertebrates
led him to a new definition of life. For Lamarck, the
simplest organism demonstrated the minimum conditions
necessary for life; lacking any specialized
organs, they depended entirely on the movement of
subtle fluids in the environment to maintain their
organic movements. The next logical step was to
move to a belief in spontaneous generation. If the
subtle fluids could maintain this simple form of life,
why could they not also create it when the circumstances
were right? The extinction issue came in when
Lamarck realized that these organisms were killed in
bad weather. The only way he could account for their
reappearance was by spontaneous generation. A belief
in spontaneous generation was necessary for a
theory of evolution, unless one wished to invoke a