26 



INSTINCT. 



the final cause cannot be substituted for the 

 physical in physiology any more than in other 

 sciences ; and this is what was meant by the 

 assertion of Bacon, that the doctrine of final 

 causes is sterile. The object of physiology is 

 to explain, not why, but /tow, the various func- 

 tions of life are carried on. But when the laws 

 of life are even partially ascertained, and their 

 application understood, i. e. when physiolo- 

 gical facts are referred to their physical causes, 

 they afford many proofs of design and con- 

 trivance, and so furnish a most important ad- 

 dition to the general science of final causes. 



The science, relative to living bodies, which 

 may truly be said to have its foundations laid in 

 the study of final causes, is the science of Com- 

 parative Anatomy, or of animal morphology; 

 i. e. the exposition of the modifications which 

 the general type of animal structure, and the 

 plan of the functions carried on in that structure, 

 undergo in the different classes of animals, and 

 by means of which the objects of the animal cre- 

 ation are accomplished by the laws of physio- 

 logy throughout the whole extent of creation. 

 These modifications are determined by the cir- 

 cumstances in which animals are placed on the 

 one hand, and by the purposes which they are 

 to serve in the creation on the other. Every 

 variation of structure has its use, in reference to 

 one or other of these objects, and the branch of 

 natural history which consists in the descrip- 

 tion and arrangement of these varieties cannot 

 be properly treated otherwise than by keeping 

 their uses constantly in view. 



Thus, in regard to the function of digestion 

 in the higher animals, its physiology, properly 

 speaking, consists in reference to the laws of 

 sensation, of instinct, of muscular motion, of 

 secretion, as modified by changes in the condi- 

 tion of the nervous system, of absorption, and 

 of vital affinities and assimilation so far as 

 they are known, by which the reception of 

 aliment, and the changes on the aliment re- 

 ceived into the body are effected ; in this en- 

 quiry our object is explanation, and however 

 useful the observation of the purpose served by 

 the organs of digestion may be, in suggesting 

 enquiries or experiments by which the laws of 

 which we are in quest may be made out, it is 

 an interruption, not an assistance, to refer to 

 these purposes, or to the importance of the 

 function in the animal ceconomy, as if we thus 

 obtained an explanation of the phenomena : 

 but when these different laws of vital action 

 are explained, their adaptation to the object in 

 view is properly stated as a branch of the doc- 

 trine of final causes. And when we trace the 

 modifications which the organs and function of 

 digestion undergo in the different tribes of ani- 

 mals, in the carnivorous, the herbivorous, and 

 the graminivorous, in the quadruped, the 

 bird, the fish, the insect, the polype, &c., and 

 compare these with the provisions for assimila- 

 tion and nutrition in vegetables, our object 

 is merely description, and the arrangement by 

 which we must be guided in this department of 

 natural history is clearly laid down by atten- 

 tion to the purposes which these modifications 

 are intended to serve, as adapted to the circum- 



stances and to the offices of animals, i. e. to 

 their final causes. 



As, in this science of morphology, or in 

 tracing the varieties of " metamorphosed sym- 

 metry," we do not seek to assign the physical 

 causes of any phenomena, it is no abuse of the 

 doctrine of final causes to assume it as the 

 basis of our arrangements ; and that the prin- 

 ciple of the unity of plan in the animal crea- 

 tion, without the study of the conditions of 

 existence of the different tribes of animals, by 

 which it is modified, and of the instincts ac- 

 companying each modification, is truly sterile, 

 was clearly shewn by Cuvier, and has been 

 ably illustrated by Mr. Whewell.* 



This observation is strictly applicable to the 

 instincts of animals, considered as an essential 

 element in their physiology. \\e obtain no 

 explanation of the phenomena of instinct by 

 referring to their use, or final cause ; but the 

 inferences drawn from the study of instincts, 

 as to the existence and attributes of the 

 Author of the universe, and the insight we 

 thus acquire into the arrangements of the 

 animal creation, are not, on that account, the 

 less certain or the less important. 



In order to perceive the extent and import- 

 ance of these inferences, it is necessary to con- 

 sider, as has been stated above, not only the 

 mutual adaptation of structure and instincts to 

 each other, but also the adaptation of both, in 

 the case of every animal, first, to the purposes 

 of its own ceconomy, and secondly, to the 

 purposes which it is fitted to serve in the 

 general ceconomy of nature. 



Assuming, as we may safely do, that one 

 great object, if not the most essential object, 

 of all the arrangements of organized beings is 

 to secure the greatest possible amount of sen- 

 tient enjoyment throughout the world, the 

 varying instincts and powers by which animals 

 provide themselves with food will appear on 

 consideration to be better adapted to the attain- 

 ment of this end than they could have been on 

 any other plan, consistently with the general 

 laws, that animal enjoyment depends on the 

 maintenance of organized animal structure, and 

 this on the continual appropriation and assimi- 

 lation of previously organized matter. The 

 different races of animals are widely diffused 

 over the globe by the powers which have been 

 granted them of indefinite reproduction. Those 

 of them which are immediately dependent on 

 vegetables for subsistence are naturally limited 

 by the extent of surface over which vegetation 

 is spread ; and when this limit has been at- 

 tained, the only expedient that can increase the 

 number of animals (and it may be added, one 

 which at the same time varies and multiplies 

 the kinds of animal enjoyments) is to make 

 animals prey on one another, either in the 

 living or dead state. " Such is the command 

 given," says Dr. Iloget, " to countless hosts 

 of living beings which people the vast expanse 

 of ocean; to unnumbered tribes of insects which 

 every spot of earth discloses ; to the greater 

 number of the feathered race, and also to a 



* Ib. p. 472, et seq. , 



