EVOLUTION OF THE HUMAN FORM. 501 



traversing the universe, we should find beings akin to ourselves in many 

 a remote corner of space. 



On the earth, indeed, life exists under conditions which may be 

 widely departed from in many other planets. Here the extreme range 

 of favoring temperature is that between the freezing and the boiling 

 points of water, the practical range being much smaller. Special con- 

 ditions of surface material and formation, atmosphere, chemical action, 

 etc., are also necessary. It is far from certain that the same conditions 

 are necessary everywhere. Life may perhaps flourish on other planets 

 under quite different conditions of temperature, gravitation and chem- 

 ical action. It is true that, if all the spheres of space are made up of 

 essentially the same chemical elements, as spectrum analysis seems to 

 show, the range of life conditions can not greatly vary. Yet if the 

 more abundant and active elements in any sphere differ from those of 

 the earth, the consequent life conditions might vary accordingly and 

 life exist under relations of temperature and chemical action unknown 

 to us. The one thing essential, in every case, is an environment favor- 

 ing organic chemism. 



All this, however, is a side issue. It has no necessary bearing upon 

 the question of animal form. If human beings could exist on some 

 planets at 1000° instead of 100° F., and be made up of a protoplasm 

 of quite different chemical composition, their forms and modes of 

 action might still be closely the same. For the external forms of ani- 

 mals are due to physical, not to chemical, conditions. They are mainly 

 results of the struggle for existence, and the effort to gain the most 

 effective formation for the incessant battle of life. This must go on 

 wherever life appears and develops, wherever the temperature or the 

 active chemical elements may be. Much the same may be said of 

 internal development. It seems to us that in any advanced stage of life 

 the energy of animal motion must be a consequence of chemical change, 

 due to something equivalent to oxidation of the tissues. There must 

 also be an efficient agency for the supply of fresh nutriment to the 

 wasting tissues, nerves for sensation and muscles for action, excretive 

 and reproductive organs, etc., in short, organic conditions analogous 

 to those which exist in our own bodies. 



In truth, the minuteness of the earth as a planet, and the seeming 

 insignificance of its life story as compared with that of all spheres and 

 all periods, are apt to give us a false impression of the real signifi- 

 cance of the development of life upon our place of abode. Though 

 the process of organic evolution here may seem to us a minor one, a 

 review of its history will serve to show that it has been a major one. 

 And its final outcome in man can hardly be looked upon as a fortuitous 

 result, but seems rather the inevitable consequence of an innumerable 

 series of experimental variations. The life period upon the earth has 



