CONCLUSIONSThe basic problems of mechanical model-making to simulate a living system
arise from the general situation that one is trying, with a completely or partly
stable model, to reproduce a completely unstable circumstance. No engineer
would consider constructing a bridge, or the frame of a vehicle, or an aeroplane, as a mechanism with loose joints and actuators, and then maintain the
required configuration by a multitude of stress and deflection recorders
backed by a computor; yet this is the situation which exists in most, if not
all of the living structural systems. It would not, for example, be possible to
make an accurate working model of a gliding bird without fitting it with an
automatic pilot to alter the shape of the wings in flight. The living system,
with no vertical fin behind the centre of gravity, has no inherent stability in
yaw; without continuous control it would be unable to regain a stable flight
path after any disturbance. This instability is in fact demonstrable in a model
glider if the fin is removed. A real mechanical model can be valuable when
used to test or demonstrate a theory of animal function, but a successful model
provides no proof of the correctness of the theory as applied to the animal.
Hypothetical models, such as the hydraulic analogues which have been used
in the explanation of bird behaviour, can be dangerous, because one can
easily become tied to ones model, and because one will tend to strain both
the properties of the model and the interpretations of experiments, rather
than face the fact that the model is, and can never be more than, a crude
representation of some particular feature of a complex system. One tends to
forget that the model was originally conceived as a tangible analogue in order
to facilitate description.Ideally ones mechanical analogue should never be needed, except for
demonstration, in other than hypothetical form, since if its design is complete
its properties are entirely predictable. In practice there may be so many
variables that theoretical analysis is impractical, and it is profitable to construct a real model and then examine its properties. One should, in most
cases, examine the model with the aim of finding differences between its properties and those of the animal. There follows then the decision as to whether
these differences are due to special features of the model or imperfections in
the theory. The best one can hope for, in most cases, is that the model will
reveal unexpected properties which are paralleled by similar features of the
living mechanism not previously noticed.
| BOETTIGER E. G. ( 1952). Biol. Bull., Woods Hole. 102, 200-211.|
| GRAY SIR JAMES. ( 1946). J. Exp. Biol. 23, 101. ( 1953) How Animals Move. Camb. Univ.
| GROVE A. J. &
NEWELL G. E. ( 1936). Annals and Mag. Nat. Hist. Ser. 10, 27, 280.|
| HARRIS J. E. ( 1936). J. Exp. Biol. 13, 476.|
| HOLST E. VON. ( 1943). J. fur Ornith. 91, 406.|
| PRINGLE J. W. S. ( 1938). J. Exp. Biol. 25, 144.|
| PRINGLE J. W. S. ( 1957) Insect Flight. Camb. Univ. Press.|
| TAYLOR SIR GEOFFREY ( 1951). Proc. Roy. Soc. A. 209, 447.|
Questia, a part of Gale, Cengage Learning. www.questia.com
Book title: Models and Analogues in Biology.
Contributors: Society for Experimental Biology - OrganizationName.
Publisher: Academic Press.
Place of publication: New York.
Publication year: 1960.
Page number: 82.
This material is protected by copyright and, with the exception of fair use, may
not be further copied, distributed or transmitted in any form or by any means.