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De Arachniden - Systematiek

The Arachnids - Systematics



Over Theorieën van Dierengedrag...


De kennis van ons eigen gedrag komt voor uit twee bronnen: we kunnen onze handelingen bestuderen bekeken door het oog van een buitenstaander, hun gevolgen voor anderen observeren en hun uitwerking op de materie nagaan; of we kunnen wat ons de redenen lijken waarom we ze verricht hebben beschouwen en het opzet, naar we geloven, waarom we ze ondernomen hebben.
Een dergelijk zelfonderzoek kan niet als een methode voor het vergaren van betrouwbare gegevens, waarop een wetenschappelijke hypothese gebouwd wordt, gebruikt worden, daar ze gelimiteerd is tot de observatie van uitsluitend onszelf, een onvoldoende basis.
Wanneer ons gedrag bovendien het observeren waard is, wanneer we bvb honger hebben, boos of verliefd zijn, dan zijn we op deze ogenblikken het minst in staat om een onbevooroordeelde en nuchtere analyse van onze motieven te maken.

De verrichtingen van andere mensen kunnen we uitsluitend van buitenaf bestuderen, een feit dat vele dramaturgen en fictieschrijvers betreuren. Toch is er zo'n opvallende gelijkenis tussen onze handelingen en de handelingen van anderen, dat het redelijk lijkt van de veronderstelling uit te gaan dat ze over een geest, die deze handelingen dicteert, en die op de onze gelijkt, beschikken. We may not be certain of this, and our uncertainty may be mildly expressed by merely remarking, as Bertrand Russell has done, that " most people would rather die than think, and in fact they usually do " ; or, it may be expressed more emphatically, as do the solipsists, who wish to deny even the existence of all persons other than themselves.

The actions of animals form a third stage. They can be studied only from without, but the resemblance between our actions and theirs is not so close. It is seen that men would not always behave as animals do in the same circumstances, and that this difference increases our doubt as to the existence of the animal mind. " It would be very difficult," writes Dale Collins, " to write a novel with the worm as hero and to get within his walls of pink skin to learn what passed there."

Some biologists do not admit any difficulty, but confidently endow the animals observed by them with co-native or with emotional or with conscious states for which there is no justification. For example, Bristowe writes of a.Spider attracted to a vibrating tuning-fork - "The owner of the web immediately rushed forth, and with considerable excitement seized upon the fork and walked up it, biting it continually and trying to find a tender spot." It is to be supposed that if we ask this observer why the Spider bit the fork so often, the answer will be, " Because it was excited." if we press the matter and ask, " How do you know it was excited ? " the only answer can be " Because it bit the fork often." In the same way, the words " trying to find a tender spot " have no real meaning. It is quite impossible to know that the Spider is trying and equally difficult to know that tenderness in the fork would induce a change in behaviour.

It may be said in defence that the writer means only that the Spider behaved as if it were excitedly seeking a tender spot; to which the obvious reply is that, since words have meanings, it is well to choose those which express what the writer wishes to convey.

There must always be an element of doubt in the interpretation of animal behaviour and a need for caution in describing what has been seen. There are three ways in which these doubts and difficulties may be diminished.

One of these is to make the naive assumption that all animals are knowing, feeling and striving subjects, similar to ourselves and differing only in degree. This is the method of vitalists, such as MacDougall, who writes, " Mind whenever and wherever it exists operates teleologically and is thus operative in all living organisms, certainly in man and probably in all animals."

The second way is to assume that organisms are mindless automata, mere physical objects governed by physico-chemical reactions, and that mind exists only in man. This is the method of all mechanists, from Descartes to Loeb and Pavlov. Its great advantage is that it. does not assume the existence of a mind where that existence cannot be proved, and it opens the way to much experimental work.

The third method is to assume that some animals are mindless automata, while some are enminded. This ought to please both sides, but it raises the difficulty of drawing the dividing line, and presents in an acute form the problem of the relation between mind and body. When these facts are considered it is not surprising that there are various theories concerned with animal conduct.

One of these is the Tropism Theory. In its extreme form the purely tropistic hypothesis cannot admit mind, or mental functions acting teleologically, as ultimate causes or governing factors in an animal's behaviour. This is the essence of mechanism. Its most confident exposition is found in the works of the late Professor Jacques Loeb, whose many experiments led him to express a theory with two principal statements:
(i) The movements of an organism to or from a centre of stimulus are caused by action of the stimulus on the receptors, and through these on the organs of locomotion, in consequence of which the animal turns until its body is symmetrically stimulated and an equilibrium obtained between the two sides.
(ii) These movements occur mechanically, as a result of physical and chemical changes in the receptors and effectors, with no real effort on the part of the organism.

Loeb endeavours to extend this conception to make it include the actions of all animals and even of human beings, an extrapolation of mechanistic biology into animal psychology, a tendency to overdrive the theory until it produces a caricature of an organism. Hence as an alternative Kühn's theory of animal taxis may be considered.

A " taxis " is a movement of an organism in response to simple external stimuli, such as light and gravity, which produce sensations in the animal. Kühn thus divided the movements of animals into four groups, named as follows:
(i) Trophotaxis: the animal directs itself symmetrically.
(ii) Menotaxis : the animal preserves a fixed direction with respect to the stimulus.
(iii) Mnemotaxis : movements in which memory plays a part.
(iv) Telotaxis : movements directed towards a goal.

It is clear that the first group of movements closely resemble the tropisms of Loeb. The distinction is based on the idea that trophotaxis involves sensation, in other words it makes the assumption that the animal has a conscious appreciation of the stimulation it receives, and turns, for example, towards the light because of the sensation of brightness and not because of the chemical changes which it produces.
Such a conception is unable to explain the fact that the behaviour of certain animals, such as Eudendrium, is in agreement with the physico-chemical law which involves the intensity of illumination. The sensation of brightness is not proportional to the intensity of the stimulus, but the concentration of the products of the photo-chemical reactions is, and the behaviour of many animals agrees with the latter, not the former.

The essential difference between the tropism theory and the taxis theory is & the former being mechanistic, the latter teleological. If difference in interpretation, a biologist can convince himself, in spite of the impossibility of obtaining direct evidence of the animal's subjective state, that the animal has a conscious appreciation of sensations, then the taxis theory will afford an acceptable appreciation of many facts.
For instance, Kühn states that flies move towards the window if they are chased and that on the theory of tropisms such a sudden change in the sign of the reaction is inexplicable, as in any other such change when it appears as a result of suddenly approaching danger.
As an innate reaction to " the simple sensation of danger," such behaviour may be intelligible.

The taxis theory cannot be accepted by those who do not admit that there is evidence for the existence of appreciation of sensations. It is, however, most interesting to perceive the similarity in behaviour of animals which move either by tropism or trophotaxis, since this may have been responsible for confusion in the past.
When similar consequences result from different causes, the difficulty of a correct explanation is greatly increased.

The modern biochemists who support the hypothesis of neo-mechanism realise, that they can only proceed in their work when they argue AS IF mechanism were true, but that in so doing they are not compelled to any dogmatic assertion as to the nature of life-processes. In the same way the behaviourists can only found a philosophically valid science in which experiment plays its proper part when they work AS IF animals are machines. They must study the results of an animal's actions and leave its purpose as unknown and unknowable.
It is in this respect that the Arachnida are the behaviourists ideal animal, for intelligence, consciousness or "mind" are practically imperceptible in all that they do.


After Th.Savory's Masterpiece "The Arachnids"


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Deze pagina's © 1999 Gie Wyckmans & Dragon Research&Development
This pages © 1999 Gie Wyckmans & Dragon Research&Development


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