May 28, 1897.] 



SCIENCE. 



815 



fare of the individual or of the species. Of 

 the countless physiological examples which 

 uiight be cited to illustrate this principle, 

 I select, almost at random, the preservation 

 of the normal temperature of the body in 

 warm-blooded animals under varying ex- 

 ternal temperatures and varying internal 

 production of heat, the regulation of respi- 

 ration according to the need of the tissues 

 for oxygen, the influence of the load upon 

 the work performed by muscles, the accom- 

 modation of the heart to the work de- 

 manded of it, the response of glands to in- 

 creased functional stimulation, the adjust- 

 ment of the iris to varying degrees of illumi- 

 nation, the influence of varying static condi- 

 tions upon the internal architecture of bone. 

 The most striking characteristic of these 

 countless adaptations is their apparent 

 purposefulness. Even if it be true, as has 

 been said by Lange, that "the formal pur- 

 posefulness of the world is nothing else than 

 its adaptation to our understanding," it is 

 none the less true that the human mind is 

 so constituted as to desire and seek an 

 explanation of the adaptations which it 

 finds everywhere in organic nature. From 

 the days of Empedocles and of Aristotle 

 up to the present time there have been two 

 leading theories to explain the apparent 

 purposefulness of organic nature — the one, 

 the teleological, and the other, the mechan- 

 ical theorj'. The teleological theory, in its 

 traditional signification, implies something 

 in the nature of an intelligence working for 

 a predetermined end. So far as the existing 

 order of nature is concerned, the mechani- 

 cal theory is the only one open to scientific 

 investigation, and it forms the working 

 hypothesis of most biologists. This theory, 

 in its modern form, seeks an explanation of 

 the adaptations of living beings in factors 

 concerned in organic evolution. What 

 these factors are we know onlj' in part. 

 Those which are most generally recognized 

 as operative are variation, natural selection 



and heredity. That additional factors, at 

 present little understood, are concerned 

 seems highly probable. The acceptance of 

 the explanation of physiological adaptations 

 furnished by the doctrine of organic evo- 

 lution helps us, I believe, in the study of 

 pathological adaptations. 



As the word ' teleology ' has come to 

 have, in the minds of many, so bad a re- 

 pute in the biological sciences, and as I de- 

 sire, without entering into any elaborate 

 discussion of the subtle questions here in- 

 volved, to avoid misconceptions in discus- 

 sing subjects whose ultimate explanation is 

 at present beyond our ken, I shall here 

 briefly state my opinion that all of those 

 vital manifestations to which are applied 

 such epithets as adaptive, regulatory, re- 

 generative, compensatory, protective, are 

 the necessary results of the action of forms 

 of energy upon living matter. The final 

 result, however iiseful and purposeful it 

 may be, in no way directly influences the 

 chain of events which leads to its produc- 

 tion, and, therefore, the character of the re- 

 sult afi'ords no explanation whatever of the 

 mechanism by which the end, whether it 

 appear purposeful or not, has been accom- 

 plished. In every case the ultimate aim of 

 inquiry is a mechanical explanation of the 

 process in question. Notwithstanding valu- 

 able contributions, especially within recent 

 years, toward such mechanical explanations, 

 we are still far removed from the attain- 

 ment of this aim. 



The knowledge of the fact that the living 

 body is possessed of means calculated to 

 counteract the efiects of injurious agencies 

 which threaten or actually damage its in- 

 tegrity must have existed as long as the 

 knowledge of injury and disease, for the 

 most casual observation teaches that 

 wounds are repaired and diseases are re- 

 covered from. It is no part of my present 

 purpose to trace the history of the specula- 

 tions or even of the development of our 



