Seeds of Hierarchy 187
as a trigger of change. The Recherches of 1802 adds the theme of "organic
movements" forming new organs and faculties in an intrinsic sequence of advance.
By the time of his most famous work, the Philosophie zoologique of 1809,
Lamarck "was explicit in portraying the diversity of animal form as a result of two
separate processes" (Burkhardt, 1977, p. 145), and he had formulated the
arguments of hierarchy and relative importance as well. The Histoire naturelle of
1815 - 1822 then consolidates and advocates the hierarchical two-factor theory even
more strongly.
In the Philosophie zoologique, Lamarck begins by claiming that, in an ideally
simple world, a single sequence of progress would regulate all taxonomic order:
It may then be truly said that in each kingdom of living bodies the groups
are arranged in a single graduated series, in conformity with the increasing
complexity of organization and the affinities of the object. This series in the
animal and vegetable kingdoms should contain the simplest and least
organized of living beings at its anterior extremity, and ends with those
whose organization and faculties are most perfect. Such appears to be the
true order of nature, and such indeed is the order clearly disclosed to us by
the most careful observation and an extended study of all her modes of
procedure (1809, p. 59).But this principle of progress remains insufficient in our actual world, where
environmental change elicits adaptations off the main sequence: "It does not show
us why the increasing complexity of the organization of animals from the most
imperfect to the most perfect exhibits only an irregular gradation, in the course of
which there occur numerous anomalies or deviations with a variety in which no
order is apparent" (1809, p. 107).
These "anomalies and deviations" are produced by a second, and clearly
subsidiary, force—a "special factor" that thwarts the "incessantly working" source
of general progress, and riddles the chain with gaps and lateral branches: "If the
factor which is incessantly working toward complicating organization were the
only one which had any influence on the shape and organs of animals, the growing
complexity of organization would everywhere be very regular. But it is not; nature
is forced to submit her works to the influence of their environment, and this
environment everywhere produces variations in them. This is the special factor
which occasionally produces... the often curious deviations that may be observed
in the progression" (1809, p. 69).
This special factor may be identified as environmental adaptation, initiated by
changed habits and abetted by soft inheritance in the principles of use and disuse
and the hereditary passage of acquired characters: "The environment exercises a
great influence over the activities of animals, and as a result of this influence the
increased and sustained use or disuse of any organ are causes of modification of
the organization and shape of animals and give rise to the anomalies observed in
the progress of the complexity of animal organization" (1809, p. 105).