Seeds of Hierarchy 189
progress builds the regular and rising trunk; diversity snatches some items off this
upward highway and pulls them into orthogonal blind alleys— "lateral
ramifications" that peter out into "isolated points": "These irregularities ... are
found in those organs which are the most exposed to the influence of the
environment; this influence involves similar irregularities in the shape and
condition of the external parts, and gives rise to so great and singular a diversity of
species that, instead of being arranged like the main groups in a single linear series
as a regularly graduated scale, these species often constitute lateral ramifications
around the groups to which they belong, and their extremities are in reality isolated
points" (1809, p. 59). The second features Lamarck's explicit statement about
hierarchy, translated into differential taxonomic levels of attention. The broad
forces of progress set relations among orders and classes; smaller and more
immediate episodes of adaptation establish species and genera:
Nature... has really formed a true scale ... as regards the increasing
complexity of organization; but the gradations in this scale... are only
perceptible in the main groups of the general series, and not in the species
or even in the genera. This fact arises from the extreme diversity of
conditions in which the various races of animals and plants exist; for these
conditions have no relation to the increasing complexity of organization;
but they produce anomalies or deviations in the external shape and
characters which could not have been brought about solely by the growing
complexity of organization (1809, p. 58).Lamarck's increasing conviction about the distinctness, hierarchical character,
and conflicting nature of the two forces culminates in his last major work, the
Histoire naturelle of 1815-1822. The force of progress has now become a
"predominant prime cause," while adaptation ranks below as occasional and
foreign, a disturbance strong enough to disrupt but not to efface nature's deeper
law:
The plan followed by nature in producing animals clearly comprises a
predominant prime cause. This endows animal life with the power to make
organization gradually more complex... Occasionally a foreign,
accidental, and therefore variable cause has interfered with the execution of
the plan, without, however, destroying it. This has created gaps in the
series, in the form either of terminal branches that depart from the series in
several points and alter its simplicity, or of anomalies observable in specific
apparatuses of various organisms (1815, in Corsi, 1988, p. 189).ANTINOMIES OF THE TWO-FACTOR THEORYWe have seen how Lamarck formulated and intensified the two-factor theory from
his first exposition of evolution in 1800 to his last and most comprehensive works.
One might even say, following a developmental metaphor, that the two sets of
forces differentiated from an originally more inchoate conglomeration of
evolutionary ideas, gradually becoming more different and