70 THE EVOLUTION THEORY 



occurred, although it was not demonstrable, and, indeed, not even 

 theoretically conceivable. This is the standpoint of the adherents of 

 the Lamarckian principle at present. 



They say there are a great number of transformations which are 

 simply and easily explained, if we regard them as the eifeets of 

 inherited use or disuse, but which admit only of a strained explanation, 

 and sometimes of none at all, on the basis of natural selection, and 

 these are not a few isolated cases, but whole categories of them. 



I will submit a few of these, and show at the same time why I 

 cannot regard them as convincing, even if it be the case that we are 

 not at present in a position to explain them without the aid of the 

 Lamarckian principle. But let me hasten to add that it is my belief 

 that we can do this, although certainly not without first giving 

 a somewhat extended application to the principle of selection. 



It has often been maintained that the existence of animal 

 instincts is in itself enough to prove that the Lamarckian principle 

 is operative. In one of the earlier lectures I showed that at least the 

 greater number of instincts must have originated in purely reflex 

 actions, and therefore, like these actions themselves, can only be 

 explained through natural selection. A reflex action, such as cough- 

 ing, sneezing, shutting of the eyelids, and so on, differs from an 

 instinctive action in the lesser complexity and shorter duration of the 

 series of movements liberated by a sense-impression, and also in that 

 it does not require to enter into consciousness at all ; but no very precise 

 boundary can be drawn between the two, and, in any case, both 

 depend, as we have already seen, on a quite analogous anatomical 

 basis. It is only a diiference in degree whether, at the sight of 

 a rapidly approaching object, the muscles of the eyelids contract, and 

 by shutting the lids, protect the eye, or whether the fly, which we 

 intend to seize with our hand, is impelled by the sight of the rapidly, 

 approaching shadow of the hand to fly quickly up. The action of the 

 fly may be regarded as reflex, or equally well as instinctive. But 

 there is also only a difference in degree, not in kind, between this 

 simple action and the complex and protracted behaviour of a mason- 

 bee, the sight of whose colony impels her to fly out and fetch clay, with 

 it gradually to build a neat cell, to fill this with honey, to lay an egg 

 in it, and finally to furnish the cell with a roof of claj^ Since all reflex 

 mechanisms, and all the natural instincts of animals, contribute to the 

 maintenance of the species, and are therefore useful, their origins 

 must be referable to natural selection, and we have only to ask 

 whether they must be referred to it always, and to it alone. 



It cannot be doubted that, in Man, and in the higher animals 



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