Presidential Address. 3 



Heredity, it must be admitted, acts on the whole as an anti-evolutionary 

 factor ; it tends on the whole to keep the organism like its immediately 

 preceding ancestors. The factors that guide the progress of Evolution must 

 then lie outside the organism. 1 



While the mapping out of the path along which evolutionary progress has 

 taken place is the special work of the morphologist, the investigation of these 

 various factors which bring about progress along that path lies rather with 

 the physiologist, by which term I mean the investigator of living things in 

 relation with environmental conditions. The environmental conditions afford 

 an all-important part of the field of inquiry. To endeavour to investigate 

 Evolution scientifically without at every step taking these conditions into 

 account, is a task of the same order as would be an investigation of 

 gravitation in which account was taken of the masses of the attracting bodies 

 while the distances between them were ignored. The mere laboratory, or 

 garden, or museum worker, may give valuable aid to the study of Evolution 

 by adding to our detailed knowledge of the phenomena of variation, but he 

 cannot get near the main question, that of the factors which are at work 

 stimulating and guiding evolutionary change. This problem lies before 

 the physiologist in the broad sense of the term. It is observers of this type 

 which are above all things wanted at the present time — highly skilled and 

 highly trained field naturalists who will devote their lives to the study 

 of organisms in their natural environment. 



We have at present before us one and only one purely scientific theory 

 of the role of environment in relation to evolutionary change. By " purely 

 scientific," I mean a theory which is merely an expression of known fact, 

 a theory which does not involve the assumption of any factor the existence 

 of which has not been demonstrated. The theory in question is of course the 



1 There is from the philosophical point of view nothing objectionable in the assump- 

 tion of an inherent tendency in living substance to evolve along definite lines. The 

 philosopher, in speculating upon the evolution of the Universe as a whole (including in the 

 expression Universe the sum of all existence), is indeed driven to an assumption of this 

 kind, as it is clear that the Universe must have contained within itself from the beginning 

 the potentialities of all the developments which have subsequently become apparent. 

 What is a logical necessity when indulging in speculations upon the evolution of the 

 Universe as a whole ceases to be so when we deal with only a part of it, such as, e.g., the 

 world of living beings. There is now — in addition to the existences whose evolution we 

 are studying — an environment, and as scientific investigators we are bound to restrict ourselves 

 to the scientific method, and inquire whether the explanation of evolutionary progress can not 

 be found in the inter-relationships of organisms and environment without having recourse 

 to the transcendental which lies outside the limits of Science. Such a principle as that of 

 "Orthogenesis" (in Nageli's sense) is inadmissible not because it is necessarily wrong, 

 but because it lies outside the boundaries of Science. 



