CHAPTER IV 



The next question dealt with by Mr. Spencer is that 

 of the co-adaption of animal parts (pp. 20 — 30). In the 

 moose, for instance, the heavy horns would be useless, 

 or rather a positive encumbrance, if pari passu with 

 their evolution there had not occurred a co-adaptive 

 evolution of almost all other parts of the body. In 

 consequence of this evolution the bones of the skull 

 have become massive ; to sustain the heavy horns and 

 head, the muscles, bones, and ligaments of the neck 

 have increased in size and strength, and are supplied 

 by larger blood-vessels and nerves,; all the structures 

 of the fore and hind limbs have also been correspond- 

 ingly modified, as have those of the trunk, including 

 the heart and lungs and other viscera. A thousand 

 changes have occurred, all directly referable to the 

 growth of the horns, and all directly co-adaptive. So 

 with all other animals ; with the evolution of the 

 elephant's trunk there has proceeded such an evolution 

 of all his other parts that, without the trunk, an 

 animal so shaped could not maintain existence; with 

 the evolution of the giraffe's neck has occurred a 

 corresponding evolution of his limbs and trunk, whereby 

 the animal is enabled to graze at a lofty height ; the 

 modifications in man's fore limbs have been accom- 

 panied by endless co-adaptive changes in the rest of 

 his body. Mr. Spencer discusses the question in great 



detail, and comes to the conclusion that "either there 



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