66 THE FOUNDATIONS OF ZOOLOGY 



have been thrown out of harmony with their environment by some 

 external change to which they failed to respond, and individuals 

 are often put at the greatest disadvantage, or even destroyed, for 

 the good of the species as a whole, but there is not a single 

 example of the disadvantageous modification of a species in a 

 state of nature ; although man is able to produce, for his own 

 purposes, such monsters as double flowers, oranges and grapes 

 without seeds, and laying hens which never sit, and thus to 

 demonstrate that species present no inherent obstacle to injurious 

 modification. 



The Lamarckians have brought together a long list of examples 

 of the useful modification of individuals by external influences, 

 but no one has tabulated the neutral or hurtful modifications. 

 Still we find reason to believe that organisms do tend to respond, 

 in a favorable way, to certain external changes, and we may fairly 

 call upon the Lamarckian to explain how this useful property was 

 acquired. How, for example, did our muscles acquire the ten- 

 dency to become strengthened by exercise ? 



Certain zealous Lamarckians tell us, as if it were a sufficient 

 explanation, that the benefit which comes with the normal use of 

 our muscles is due to the properties of living matter ; although I 

 am not aware that any modern naturalist attributes it to anything 

 else. I shall try to show, Lectures VIII. and IX., that the only 

 path in which we can have any well-grounded hope for progress in 

 the explanation of adaptive types takes its departure from that con- 

 ception of nature which leads us to seek for the origin of the 

 properties which exhibit adaptation in the physical basis of living 

 beings. If any interpret the opinion that the origin of these 

 properties must there be sought as an assertion that it has there 

 been found, I do not see that their impetuosity has any bearing on 

 the point at issue, which here, as in other cases, is the question 

 how the living being comes to exhibit these properties under 

 normal stimuli in such a way as to be adaptive. The increased 

 power to use our muscles, which comes with practice, is, no doubt, 

 due, in the main, to improvement in the nervous system, although 

 normal use is essential to the healthful development of the muscle 

 itself, for its nutrition is promoted by normal exercise, and this 

 result may be imitated by massage or by electrical stimulation. 



