20 tHE COMING OF MAN 



development. We will not weary ourselves with dry details 

 of anatomical structure; we seek chiefly the tendency and 

 results of his experiment and line of advance, his gains and 

 losses. The ancestral clam developed a shell composed of 

 two valves which extended downward and completely cov- 

 ered the sides of the body. It burrowed in the mud or sand 

 until well out of reach of any large foes — if any such should 

 ever arise — where he was safe even from nibbling worms 

 and boring irritating animalcules. Against all forms of pain 

 and discomfort he offers an even more impregnable defence. 

 He has little muscle, except enough to close the shell, less 

 nerves, and his supra-cesophageal ganglion is minute. Most 

 irritations are unnoticed; severe or sharp pain is probably 

 impossible. 



Some morbid soul may think that a being to whom pain is 

 impossible cannot know happiness or pleasure. The clam 

 distinguishes his food, and his senses are continually tickled 

 by a stream of appetizing particles floating down his throat. 

 Fear and worry are certainly unknown to him. If unalloyed 

 comfort is the goal of evolution, the process should have ended 

 with the clam. 



The criterion of fitness, according to Mr. Darwin's theory, 

 is survival due to conformity to environment. This the bi- 

 valve mollusks have attained, and without any great effort or 

 struggle. They were already ancient forms when the first 

 mammals appeared some millions of years ago. They have 

 lasted well. They have a large surplus income to devote to 

 reproduction. The eggs are small because the young can be 

 born in a very simple stage and still shift for themselves. 

 The infantile danger period is short. They have been fruit- 

 ful and multiplied. 



Many animals have found a temporary environment of 

 abundance and comparative peace, to which they have closely 

 conformed, and have therefore prospered. But when condi- 

 tions changed, they were the first to suffer and disappeared. 

 The clam has accommodated itself to life in a strip of shore 

 where sea and land meet. As long as sea and land endure 



