The Rodentia in Evolution 47 



but in time, and hence should be observable in animals and 

 plants of to-day. It may be properly noted that biology is 

 a young science, and that very accurate observations would 

 be required to show^ that evolutions at the present time are 

 not taking place as w^ell as to show the converse. In view 

 of the great variability of animals and plants, it seems 

 almost strange that anyone should suspect that fixity in 

 animal form is a law of life, and yet in spite of the variabil- 

 ity in individuals, the lines of specific form run remarkably 

 true,, many species being almost or quite unchanged, as can 

 be shown by sundry data, for many thousand years, and the 

 recognition of this fact has helped the native conservatism 

 of the human mind to hold to the position of immutability 

 of animal species with wonderful tenacity. The reason for 

 this is found in the fact that the observations on which the 

 proof of evolution rests are more unusual, hence while 

 students almost universally accept the theory as a working 

 hypothesis, it only slowly gets abroad among the notions 

 of mankind. 



If any great group of animals be examined at all thor- 

 oughly their relations are unintelligible, except on the evolu- 

 tion hypothesis. It was the suggestion of Professor Louis 

 Agassiz, the great opponent of Darwin, that the likeness of 

 animals and their dissimilarities were indications of an ideal 

 or mental connection between them due to their production 

 by the same maker, just as the similiarities in style of works 

 of art owe their existence to unity, not in the objects, but in 

 the producer. It is necessary on this theory to believe that 

 each kind of animal was produced in the first instance with 

 special reference to the station it now inhabits, and all its 

 structure must show evident reference to that specific end, 

 and no other. It is late in the day to be proving evolution 

 to the professional zoologist, but as these pages are intended 

 partly for the laity, these commonplaces may, I trust, be 

 pardoned. The consideration of any group of animals 

 shows that while Agassiz's theory of the cause of classifica- 

 tion is ingenious, it is also highly improbable, because many 

 facts go to show that animals judged by the standard of 

 structure are but poorly designed to occupy the situation 

 they occupy if they were originally designed to be such 



