806 



SCIENCE 



[N. S. Vol. XL. No. 1040 



the individual have been coordinated for the well- 

 being of that individual. Such coordination has 

 taken place in two ways: (1) a chemical method, 

 by the formation of hormones; (2) a nervous 

 method, by the formation of a central nervous 

 system, and it is self-evident that as soon as a 

 central nervous system is formed, such nervous 

 coordination, especially in connection with the 

 formation of the special senses of sight and smell, 

 must become the important factor in the life of 

 the individual, and its further and further de- 

 velopment must constitute the most important 

 factor for the upward progress of the animal 

 Tace.3 



The fundamental importance of this idea is 

 likely to be lost for the general reader in the 

 almost platitudinous simplicity of the state- 

 ment. In reality, there is much matter for 

 long and profound reflection. The idea of 

 chemical coordination, although of compara- 

 tively recent development, has claimed the 

 attention of a host of workers, partly perhaps 

 because of its novelty, and the nervous mechan- 

 ism has, by contrast, become a neglected field. 

 But in the development of the purely chemical 

 mechanisms of coordination, so far as they 

 have been traced at present, we find that they 

 reach their maximum efficiency and com.- 

 plexity well down in the mammalian phylum. 

 It is probable that, so far as the purely chem- 

 ical mechanisms are concerned, man is not a 

 more complex animal than the rabbit, and 

 certainly not a more complex animal than the 

 dog. Yet the total difference between man 

 and the rabbit or the dog is considerable. The 

 reason for this difference is not far to seek. 

 It lies in the difl^erence of the nervous systems 

 of the two forms, and in the interaction of 

 this system with the chemical mechanisms of 

 coordination. After the chemical mechanisms 

 have reached their zenith, the nervous system 

 still shows, step by step, an increasing com- 

 plexity, functionally as well as structurally, 

 as successively higher types of animals are 

 examined. 



I walked out to Dr. Gaskell's house from 

 Cambridge early one August afternoon two 

 years ago, intending to make a brief call, but 



3 Proceedings of the Linnean Society of Lon- 

 don, Session 122, 1909-10, p. 9. 



the afternoon was far gone and the sun low 

 in the west before I started for the little rail- 

 road station at Great Shelford. The conversa- 

 tion turned on the role of the internal factors 

 in evolution. He remarked: 



It is not size, it is not strength, that has con- 

 ferred the great advantage in the struggle, but 

 aeuteness. 



The hand and arm of man are often cited 

 as adaptations of a high degree of perfection 

 conferring a great advantage upon its pos- 

 sessor. This is but a part of the story. The 

 hand and arm without a nervous system to 

 control or coordinate its movements would be 

 valueless. The hand and arm of a recent 

 hemiplegic may have lost little or nothing in 

 bone or muscle, but, despite its complex struc- 

 ture, it is of less use to its possessor than the 

 foreleg and hoof of a horse. The clot of blood 

 in the cerebrum has wrecked the mechanism 

 which also is necessary if the marvelous hand 

 of man is to be of use to him in the struggle 

 for existence. Nor would the combination of 

 the man's hand and the dog's brain be a more 

 tappy one. The feeble-minded and the idiotic 

 often show but slight and unimportant phys- 

 ical modifications aside from those found in 

 the brain. When looked at from the point of 

 view of its functional relations to the whole 

 organism, or from the point of view of its use 

 to the possessor, neither hand nor motor nerv- 

 ous system alone is significant, but it is the 

 combination of the two — the coordination — 

 that is the important thing. And in addition 

 to the mere manual skill arising from the 

 steady nerves and the strong hand, the faculty 

 of looking into the future — ^the aeuteness and 

 accuracy of mental vision — constitutes a 

 valuable adjunct to the possessor of an organ- 

 ism whose chemical mechanisms of coordina- 

 tion give rise to no physical discomforts. The 

 nervous mechanisms of coordination, as well 

 as the chemical, will surely claim the serious 

 attention of the student of evolution from its 

 functional side. And it is not single struc- 

 tures or organs alone which become significant 

 in evolution, but the coordination of all parts 

 of an organism. 



