20 R. 0. HOSKINS 



Evolution of Hormone Control 



A consideration of the action of the various hormones suggests an 

 interesting speculation: Have the chemical products been evolved to 

 govern the reactions and growth changes to which they give rise, or have 

 these latter been secondarily evolved in relation to the hormones? The 

 latter is the more probable assumption, and in case of certain of the non- 

 specific metabolites has been definitely proved. For instance, carbon 

 dioxid production occurs in animals at the very bottom of the scale of 

 life, whereas respiratory movements which are regulated by this com- 

 pound appear much later. It is not unlikely that in case of the internal 

 secretions, proper, evolution has taken a similar course. Certain body cells 

 we may suppose, in carrying out their peculiar life processes, have come 

 to form unusual products. The body has then developed adaptive reac- 

 tions to these products. The possibility that epinephrin formation may 

 be merely one phase of a detoxication reaction in relation to which the 

 phenomena postulated in Cannon's "emergency theory" have been sec- 

 ondarily evolved, has been discussed in a preceding paragraph. At any 

 rate, it is true that in certain animals are found substances capable of 

 exerting a marked influence in organs which these particular animals do 

 not possess. Thus it has been found that extracts of the hypophysis of 

 fishes or birds have a marked influence on lactating mammary glands, 

 an influence due apparently to a substance identical with that found in 

 extracts of the hypophyses of mammals, but obviously a galactagogue can 

 be of no use to a fish or a bird. 



Starling has suggested the probability that hormone control of body 

 functions was first evolved and that nervous control was later superim- 

 posed. In forms even as low as the sponge there are found cells that 

 migrate from one part of the body to another in response to changes in 

 the chemical state of the tissues. In higher animals the migration of 

 leucocytes to a locus of infection is a similar reaction. In favor of 

 Starling's hypothesis may be cited the fact that hormones do affect more 

 particularly the primitive functions, such as growth, digestion, and 

 reproduction. 



In case of many bodily activities chemical control would be inadequate. 

 For example, if a missile were rapidly approaching the eye there would 

 bo little use in an arrangement whereby some chemical product were dis- 

 charged into the blood stream and then carried to the muscles to stimulate 

 them to activity. The impending injury would have occurred before 

 any protective reaction could take place. Moreover, the muscles as a 

 whole would be affected rather than those few necessary to avoid the 

 missile. To meet the more sudden vicissitudes of life, therefore, nervous 

 reflex control has been evolved. 



