APPENDIX D 217 



infant as regards inborn characters ; but as regards almost all the 

 structures of the trunk and limbs, and most of those of the head, 

 the difference is in characters which have been acquired by the 

 adult in response to the stimulation of exercise and use. Thus, 

 the limbs develop wholly in response to use, the heart and 

 arteries develop within certain limits in proportion to the strain 

 put on them, as also do the lungs and their accessory muscles, 

 as well as the bony attachments of the latter. The muscles, 

 arteries, nerves, etc., of the head and neck also develop in 

 response to the same stimulation. Moreover, the normal 

 standard of development is maintained only as a response to 

 this stimulation (i.e. use, exercise), for example, when not 

 used, the muscles, with their co-ordinated structures, atrophy and 

 tend to disappear, as in the case of a paralysed limb. It may be 

 added that it is probable that even the infantile standard of 

 development is, to some extent, acquired under the stimulus of 

 foetal movements in utero. 



In upholding the doctrine of the transmissibility of acquired 

 modifications, much stress has been laid by Mr Herbert Spencer 

 and others on the exquisite co-ordination of the multitudinous 

 parts of the high animal organism. They maintain that this 

 co-ordination affords decisive proof of the Lamarckian theory, the 

 line of argument being as follows : It is not probable that the many 

 structures of a high animal can ever have varied favourably 

 together (as compared to the parent) in any individual animal. 

 It is unbelievable that they can all have varied favourably 

 generation after generation in a line of individuals. A chain is 

 only as strong as its weakest link. A favourable variation, say, a 

 larger horn in the elk, if unaccompanied by corresponding 

 variations in all the thousand parts (in head, neck, trunk, limbs) 

 co-ordinated with it, would be useless, and even burdensome. In 

 other words, if a single structure (muscle, bone, ligament, etc.) 

 of all those associated with the larger horn failed to bear the 

 strain of it, the larger horn would not favour survival, but, on the 

 contrary, would be a cause of elimination. Therefore, say these 

 thinkers, the evolution of high multicellular animals cannot be 



