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 correspondingly 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 accompanied 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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