5o8 POPULAR SCIENCE MONTHLY. 



period over which this evolution has extended, the extraordinary va- 

 riety of forms which have appeared, and the strict limitations of the 

 problem by natural influences, chemical, meteorological and vital, it is 

 not easy to perceive how the final result could have deviated widely 

 from that which we have before us. If the process were gone over again 

 upon the earth, the great probability is that it would end once more 

 in the mammalian quadruped. On other planets different chemical 

 and physical conditions might affect the result, though the general 

 principles of vital action could not greatly deviate and the evolution 

 of the organs would doubtless pursue much the same course. As re- 

 gards external form, the struggle for existence must operate in the 

 same way and probably to the same effect. 



Let us, for example, take the head of the quadruped, with its facil- 

 ity of motion, its apparatus for mastication, its sense organs, its nerve 

 center. Can any one suggest an improvement upon the general ar- 

 rangement of these organs, the ultimate outcome from a myriad of 

 experimental efforts? The nasal openings stand above the mouth, in 

 the best position to give warning of dangerous odors from food. The 

 eyes are placed at the highest altitude and in the frontal position, the 

 best location for their special duty. The ears are situated to catch 

 sounds from the rear and the front, but preferably the latter. The 

 brain is situated in the immediate vicinity of these organs of special 

 sense, as if to favor quickness of sensation. All the organs of the 

 head, indeed, seem remarkably well placed and adapted to their par- 

 ticular duty, and when we consider the varied positions which these 

 organs have occupied in lower forms of life, we may justly look upon 

 those in the quadruped as the final 'posts of vantage' resulting from a 

 multitude of trials. Similar deductions might be made from other 

 sections of the body, internal and external. 



But we have not yet reached the evolution of a thinking being, an 

 animal dependent much more upon its mental than upon its physical 

 powers. In each advanced type of animal some mental progress was 

 made; largest of all in the quadruped mammal; yet even in the latter 

 it ended at a low stage. This is evident if we compare the quadruped 

 with man, the former dependent very largely upon its physical, the 

 latter mainly upon his mental powers. Evidently, in any planet, some 

 step of progress beyond the quadruped was necessary for this result. 

 On the earth this step was towards the form of man, the only true 

 biped. May it not have been different in other planets, yielding human 

 beings widely diverse in form and general bodily relations? 



The answer to this query depends upon that special characteristic 

 to which man — wherever found — owes his superiority. His physical 

 difference from the lower animals is by no means great. It consists 

 principally in an adoption of the upright attitude, a reduction of the 



