Proofs of Evolutio7i. 293 



What is true of the toes of the horse applies as well to 

 the development of other parts of his structure. The prin- 

 ciple applies not only to him, but to all living things. 

 Descent with modification is a universal law. By the 

 necessity of continually varying his modes of life, the 

 horse has advanced from a useless little plantigrade quad- 

 ruped to the position of the greatest help-mate of man, 

 bearing patiently his many burdens and contributing in no 

 small degree to his pleasure. But Evolution, which fash- 

 ioned the horse and made him man's burden-bearer, is also 

 raising up friendly inventors to emancipate him from some 

 of his heavy toil. 



All the organs, as well as all the parts of the skeletons 

 of all animals, have undergone slow and gradual changes, 

 from the simplest beginnings up to their present complex 

 state. New and ever-changing environments have brought 

 corresponding modification of the organs or parts. Those 

 no longer needful, shrunk to rudiments, finally disappeared 

 altogether. Those needful and used were strengthened 

 along their several lines of growth, until we have to-day all 

 the wonders of form and function. 



Nature never begins her work de novo, for her adaptive 

 genius is so great that she can transform the old into the 

 new. When she wanted to make a landsman of a fish, she 

 did not give him a new pair of legs at once, but left him to 

 utilize his fins for that pur})Ose as best he could. Of course, 

 he made bad work of it at first ; but as he was left in the 

 hard grip of necessity it was Hobson's choice. As he was 

 often left on shallow, muddy shores by receding tides, he 

 began to work his fins more vigorously, until finally, after 

 many generations, in spite of a round of fatal failures, 

 some of his kind succeeded in adapting their fins to this 

 new use. The mud-fish of India, the Brazilian doras, and 

 certain catfish of tropical America, take journeys of con- 

 siderable length across the dry land in this way. Thus tlie 

 swim-bladders of certain of the early fishes gradually devel- 

 oped into lungs, the gill-arches into ears ; the head enlarged ; 

 the circulation increased ; a warmer current filled the veins ; 

 the tail-fin, not having miich to do, dwindled to an orna- 

 mental appendage, — and then and there a quadruped was 

 born. 



Again, when Nature wanted a bird, she didn't make one 

 out of raw material, as we are told, full-winged to soar 



