186 THE STRUCTURE OF EVOLUTIONARY THEORY
directions—up the ladder of progress, and sideways into lateral paths of adaptation.
Lamarck may never have completed his scheme with success and consistency, but
he made his desires clear to the point of redundancy. Lamarck's two-factor theory
holds the distinction of being both the first evolutionary system in modern Western
thought, and a strong argument for causal hierarchy. The two levels—in strong
contrast with modern theories of hierarchy—are both causally distinct and
contradictory for Lamarck, thus inspiring Darwin's legitimate disparagement.
Lamarck's distinction of levels, as discussed in the next section, unites hierarchy
and evolution at the starting gate of the subject's modern history.
LAMARCK'S TWO-FACTOR THEORY: THE HIERARCHY OF
PROGRESS AND DEVIATIONLamarck had separated his sets of forces in order to account for the two primary
attributes of natural order—features that seemed to play off against, or even to
contradict, each other. First, organisms form a progressive sequence from mo»ad
to man, but the sequence abounds with gaps and deviations—so some other force
must be disrupting a potentially smooth gradation. Second, organisms are well
adapted to their environments, but most adaptations, from the tiny eyes of moles to
the legendary necks of giraffes, represent particular specializations and departures
from type (with many adaptations counting as losses or degenerations); therefore,
adaptation cannot account for the sequence of progress.
Lamarck joined the two sets in a discordant union that operated more like a
tug of war than a harmony. This partnership made no pretense to equality. A
primary and dominating force—the march of progress—struggled to order
organisms in a simple and sensible way; while a secondary and disrupting force—
l'influence des circonstances, or adaptation to local environments— tore this order
apart by pushing individual lineages into lateral deviations from the main track,
thereby making the order of life rich, messy, and replete with clumps and gaps.
This clear distinction of merit—the regular vs. the deviant, the progressive vs. the
merely fit—imparts the character of hierarchy to Lamarck's uneasy marriage of
forces, with a primary factor doing its inexorable, underlying work at a higher
level, while a secondary but more immediate factor of disruption plays upon the
products of this higher level, pushing some forms into the side-channels of its
influence. Burkhardt (1977, p. 87) captures both the hierarchy and conflict of
forces in his epitome of Lamarck's system as an attempt to explain "how organisms
would develop naturally" along a chain of progress "were it not for the
constraining accidents of history" pushing lineages into side channels of
adaptation.
Lamarck worked his way slowly towards this final system of hierarchy and
relative importance. The Floreal lecture of 1800 states that the "principal masses"
of major taxonomic units "are almost regularly spaced" (1800, 1984 edition, p.
416), but designates some peculiarly adapted species as "lateral ramifications" and
"truly isolated points." But this lecture cites only environment