436 i Flora Unveiled
The Scottish philosopher David Hume was among the first to question the infallibility of
the mind as a reliable interpreter of external reality. Contrary to Descartes and the rational-
ists, Hume argued, in Treatise of Human Nature (1739– 40) and other works, that the mind
was incapable of pure rationality and that “[r] eason is ... the slave of the passions.” Because
of the mind’s irrational tendencies, Hume cautioned that subjective bias could never be
eliminated from scientific studies. Thus, we can never fully understand anything outside
ourselves. Even our ideas about ourselves are cobbled together from fragments of memories,
which are subjective and therefore unreliable. Hume’s skepticism served to undermine the
Enlightenment’s faith in reason and science as the only paths to truth.
In Critique of Pure Reason (1781), Immanuel Kant, attempted to rescue science from
Hume’s doubts by defining a limited set of properties or patterns of the phenomenal world
that the mind was capable of comprehending. Such “categories of understanding” included
cause and effect, space and form, time, and quantity. Outside of these categories, according
to Kant, lay the “noumenal” sphere about which nothing could be known. But within the
framework of the categories of understanding, the results of science— at least physics and
chemistry, which obeyed mechanical laws— could be shielded from Hume’s skepticism.
Kant was less sanguine about the ability of scientists to comprehend living organisms,
which did not seem to obey mechanical laws, and, for this reason, he did not believe that
biology could ever become a true science. Living organisms were thus qualitatively different
from machines. They could grow, develop, and reproduce without any external input other
than food.^19 According to Kant,
[a] n organized being is ... not a mere machine: for the latter has only the power of
motion, while the former has a formative power [Bildungstrieb], of a kind that it
imparts to material not possessed of it (it organizes these materials). Hence such a
propagative power of formation cannot be explained merely through the ability of
motion that a machine has.^20Kant had borrowed the term Bildungstrieb from a young biologist at the University of
Göttingen, Johann Friedrich Blumenbach. Blumenbach had begun his career as a prefor-
mationist but had switched to epigenesis after observing the results of surgical experiments
with the fresh water polyp Hydra, similar to those Abraham Trembley had performed
decades earlier. Struck by the ability of the polyp to regenerate lost parts, Blumenbach
concluded that:
there exists in all living creatures, from men to maggots and from cedar trees to mold,
a particular inborn, life- long active drive. This drive initially bestows on creatures
their form, then preserves it, and, if they become injured, where possible restores their
form. ... I give it the name of Bildungstrieb.^21Other authors had invoked similar vaguely defined “inborn drives,” such as vis plastica
and vis essentialis, but these terms were understood to refer to occult forces. Blumenbach’s
Bildungstrieb gained greater currency for two reasons: first, because it was adopted by Kant,
and second, because both Blumenbach and Kant insisted that Bildungstrieb was not an
occult, spiritual force, but was in some way associated with the organic matter it directed.