I
The old physiologists believed that the mind of brutes only obeyed two stimuli—pain and pleasure, and that all processes of their organism had as aim to avoid the bad and procure the good. Albrecht von Haller combated this opinion in the last century. 'This theory’, he says, 'does not in any way accord with the phenomena. If you consider the movements of an animal during fear, in imminent danger, as having preservation of life for their object, is there anything more absurd than the trembling of the knees and the sudden weakness which befalls it? I am persuaded that all phenomena of fear common to animals are not aimed at the preservation of the timid but rather at their destruction. In order to preserve a just balance it is necessary that the more prolific animals should be destroyed by the less prolific, therefore necessary that those animals destined to be the prey of others should not be able to defend themselves easily’.[15]
I think Charles Darwin must not have been acquainted with this explanation of trembling, as I am convinced he would otherwise have tried to combat it, or would at least have mentioned it in his writings. He was much too conscientious to ignore an objection made to his theories.
Here we have the example of another phenomenon which seems to contradict certain hypotheses of Spencer and Darwin. If it is true that, in the struggle for existence, animals have always perfected those capabilities which are most useful to them in defending themselves, and have gradually left behind, with the generations that have succumbed, all dispositions of the organism which were pernicious to the preservation of the species, why have they not succeeded in freeing themselves from trembling? Why, on the contrary, in critical, decisive moments, when danger confronts them, when their existence is threatened, when nothing is more imperative than flight, attack or defence, do we see animals paralysed with trembling, incapable of struggling, and perishing without their strength having in the least profited them? As Haller’s hypothesis is not sufficient to justify such a serious imperfection in organisms, we must seek the reasons and causes of this phenomenon elsewhere.