The making of models, so much a part of all the
natural
sciences, and increasingly of the social sciences, has
been a
central feature of the development of biology.
Indeed, modern biology
springs from that ur-model,
the bête-machine, described in 1637 by René Descartes:
If there were a machine that had the organs and the external
features of a monkey, or some other dumb animal, we would
have no
way at all of knowing that it was not, in every
aspect, of the very
same nature as those animals
(Discours
de la méthode,
Part V).
For Descartes, even man would be indistinguishable
from such an automaton if
it were not for his power
of communicating and apprehending complex
thoughts
by means of speech. Even this exception to the machine
model
of living organisms was challenged early in the
history of biology with the
publication of La Mettrie's
L'Homme machine (ca. 1750).
The machine-animal, and its extension the machine-
man, are more than simply examples of model and
metaphor in
biology; they are at the basis of all model-
making, for they are a statement of an underlying
relation
between effects and causes in living organisms.
It was precisely the
element of will and the infinite
variety of personal and idiosyncratic
response to exter-
nal conditions that led
Descartes to exempt man from
the constraints of such a model. Animal
behavior
seemed to him stereotyped, without variety, and totally
predictable from external conditions, so that for beasts
the relation
between cause and effect was unbroken.
Not so for man, whose essential
nature lay in his free
will. It seems reasonable, on the other hand, that
it
was La Mettrie's Jansenist training, with its heretical
denial of
free will, that made possible his inclusion of
man in the realm of
automata. As we shall see, the
Cartesian view of cause and effect, while an
integral
aspect of model-making for a large part of modern
biology,
has been replaced, for some problems, by a
weaker form of relationship
among events. These are
the so-called “stochastic”
theories in which the rela-
tionships
between events are described by probability
statements rather than by exact
one-for-one corre-
spondence. The
influence of Cartesianism is very
strong, however, and stochastic theories
are admitted
only slowly, grudgingly, and with a certain condescen-
sion toward those
“inexact” fields of biology that seem
to require
them. As in nineteenth-century physics, some
feel that uncertainty in a
system is a reflection of
epistemological rather than ontological
properties so
that with the aid of a “Laplace's
demon” it would be
possible to reformulate stochastic theories
in com-
pletely deterministic form. Thus, after 300 years,
Descartes'
original metaphor maintains its powerful
influence on model-making in
biology.
