Ninth Annual Meeting. 65 



THE INFLUENCE OF FOOD -SELECTION UPON THE EVOLUTION OF 



ANIMAL LIFE. 



BY DR. A. H. THOMPSON, TOPEKA, KANSAS. 



The influence that food-selection exercises in directing the course of the development 

 of animal life, is a factor of the principle of evolution that has scarcely received the at- 

 tention at the hands of naturalists and physiologists that its importance deserves. Its 

 potency is manifested in such a marked manner as to be, under some circumstances, a 

 prime factor in the determination of great changes in the phenomena of animal life, even 

 of catastrophes, and yet it has been relegated by most philosophic biologists, when recog- 

 nized at all, to a second or third place in the order of forces. Many are the theories that 

 have been woven and elaborated in regard to the origin and evolution of life, in the name of 

 the developmental principle, and many are the factors that go to make up the argument in 

 favor of each one. But in the table of forces acknowledged, direct, indirect and acci- 

 dental, food-selection rarely tinds a place under any name, and is still more rarely reck- 

 oned as more than an accidental influence. 



By the term food-selection we designate that power which each particular substance 

 used as food exercises in causing certain species of animals to employ it for sustenance; 

 i. e., it directs the choice of animals towards itself for sufficient reasons to induce them 

 to use it for food, such as convenience, adaptability, etc. If a given species in a certain 

 district be surrounded by a constant supply of its proper food, it is drawn towards it, 

 employs it, and lives; — the food-environment favors life. But it may not be thus per- 

 manent and favorable to the perpetuation of a certain stage in the life of a species. In 

 fact, it rarely is so, but may be changeful and inconstant. In this case, the food imposes 

 upon the animal organization employing it, the necessity of ever changing in conformity 

 to the new conditions ever being presented. The power of food to induce change in the 

 animal organism, and maintain or alter it at its own caprices, is the selection which 

 dictates change. 



The dependence of animals for life upon the food-supply, is the most apparent fact of 

 their existence. Every process of their physiology, the movement of every muscle, the 

 production of every bone or other tissue, the action of every gland or nerve-cell, the won- 

 derful processes of origin, growth and reproduction, depend for their maintenance and 

 success upon the completeness of the nutritial supply. Nutriment for the tissues, the 

 mysterious pabulum that upholds life, is derived from the food eaten, and consecpient 

 upon the acquisition of food is the continuance of life with all its ph*iomena, as well of 

 the species as of the individual. All animal life, throughout all time, has been thus de- 

 pendent, and the variation of the quantity or quality of food has caused some modiflcation 

 of all the forms that ever lived upon the earth. Its importance as a potent modifying 

 influence can scarcely be over-estimated, and is, perhaps, second only to cosmical influ- 

 ences in the potency of its eflects upon animal life. The pursuit and procurement 

 of food is the one occupation of all animals; their one object in life being the obtaining 

 of it, that life may be maintained and transmitted. Much force is expended by animals 

 in the augmentation of the species, and success in this depends altogether upon the com- 

 pleteness of the food-supply, and its proper assimilation. One of the flrst indications of 

 insufficiency of food among all animals, man included, is decrease of reproduction. 



This paramount dependence of the animal organism upon food, necessitates the adap- 

 tation of the organs of the economy that procure, reduce and assimilate it for the nutrition 

 of the tissues, to the kind of food employed. Upon this proposition rests the theory of 



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