170 MAN'S PLACE IN THE UNIVERSE 



the thought that somewhere in the universe there may 

 be other beings "a little lower than the angels" whom 

 Man may regard as his equals — or perhaps his 

 superiors. 



It is idle to guess the forms that life might take in con- 

 ditions differing from those of our planet. If I have 

 rightly understood the view of palaeontologists, mam- 

 malian life is the third terrestrial dynasty — Nature's 

 third attempt to evolve an order of life sufficiently flex- 

 ible to changing conditions and fitted to dominate the 

 earth. Minor details in the balance of circumstances 

 must greatly affect the possibility of life and the type of 

 organism destined to prevail. Some critical branch- 

 point in the course of evolution must be negotiated be- 

 fore life can rise to the level of consciousness. All this 

 is remote from the astronomer's line of study. To avoid 

 endless conjecture I shall assume that the required con- 

 ditions of habitability are not unlike those on the earth, 

 and that if such conditions obtain life will automatically 

 make its appearance. 



We survey first the planets of the solar system; of 

 these only Venus and Mars seem at all eligible. Venus, 

 so far as we know, would be well adapted for life 

 similar to ours. It is about the same size as the earth, 

 nearer the sun but probably not warmer, and it possesses 

 an atmosphere of satisfactory density. Spectroscopic ob- 

 servation has unexpectedly failed to give any indication of 

 oxygen in the upper atmosphere and thus suggests a 

 doubt as to whether free oxygen exists on the planet; 

 but at present we hesitate to draw so definite an infer- 

 ence. If transplanted to Venus we might perhaps con- 

 tinue to live without much derangement of habit — 

 except that I personally would have to find a new pro- 

 fession, since Venus is not a good place for astronomers. 



