1. Crises of the Chain of Being: The Controversies
over the Notion of Species.
We have said that for Kant
the empirical use of ideas such as that of
continuity
and of the plenitude of forms (plenum
formarum) was
illegitimate and could only make for
contradictions and
controversies. His conclusion seems to be, and
indeed
is, in part, a commentary on the eighteenth-century
discussions
of continuity and plenitude in the biological
world.
At first the new instruments of scientific research do
not seem to
contradict the idea of a Scale of Creatures.
Indeed, the already widespread
use of the microscope
makes it possible to observe the world of the
infinitely
small; and in 1739 the discovery of Trembley's Hydra
is hailed as the discovery of the missing link between
the vegetable and animal worlds. Even the skeptical
“Pyrrhonism” of men of science, or their awareness
of
the limitations of experimental research, echoes
Leibniz' vision of a
universal “plenum” of which we
have a partial vision
only. No, it is rather the debate
over the notion of biological species
that challenges
the foundations of the Chain of Being, and in
particular
the principle of plenitude. In order to salvage this
principle it was necessary to attribute only a conven-
tional, not real, value to biological classifications:
sub-
division into species would in fact
have created in
nature a too nicely spaced series, letting precisely
those
imperceptible gradations escape which assure conti-
nuity and plenitude in the natural world.
The conventionality of species is affirmed in Buffon's
Discours sur la manière d'étudier et de
traiter l'Histoire
naturelle, which prefaces the first volume
of his Histoire
naturelle (1748). The methods
or “systems” of classifi-
cation are, to be sure, indispensable but artificial: as
against
the nuances of natural reality we have an arbi-
trarily articulated series. The error of all classification
rests on the inability to grasp the processes of nature,
which are always
realized by degrees, by imperceptible
nuances, thus escaping all division.
In short, only indi-
viduals exist in
reality; genera or species do not.
But Buffon wholly reversed his position in the course
of his research,
prompted by the now general recogni-
tion of
species as a genetic entity. In fact, in Volume
XIII of the same work
(1765) he affirms that the only
true beings in nature are species and not individuals.
Robinet, a firm advocate of the principle of pleni-
tude, was quite clear about the dangers inherent in
classifications: if we accept the separation of nature
into orders of this
kind, the Chain of Being is fatally
broken (
De la nature [1766], IV, 4-5).
Doubtless the
introduction of the idea of species as a genetic entity
contributed decisively to this crisis of the principle of
plenitude: since
two individuals are said to belong to
the same species if they are capable
of producing a
fertile offspring and of transmitting to it their own
hereditary characteristics, it is hard to imagine a
“full”
concatenation among the diverse species.
Actually, in
the second half of the eighteenth century, the notion
of
species is already established and operative in the
biological sciences.
The controversies—accelerated by
the always growing body of
empirical data, and par-
ticularly by the
data of the new science of paleon-
tology—had to do rather with the fixity or nonfixity
of
the species (taken now as established entities).
