GREAT STEPS IN ORGANIC EVOLUTION 909 



CAN THERE BE LIFE BEYOND OUR WORLD LIMITS ?~ 



This old question is one too persistently recurrent to be ignored. 

 At present we have no positive assurance of the existence even of 

 water — so indispensable to life as we know it — upon any other 

 planet, save probably or possibly Mars, and no great faith in "red 

 vegetation" or anything very similar to our forms of plant-life, let 

 alone animal or human life. Moreover, all that astronomers have 

 yet discerned of other planets makes it impossible to form any 

 conception of life upon them at all comparable to ours, while of 

 planets around other suns we have as yet no evidence at all. Hence 

 it is not to be wondered at that so reflective and open-minded a 

 biologist as Alfred Russel Wallace, in no small measure nearest to 

 Darwin's own magnitude and main achievement, should practically 

 have returned to the ancient cosmogony, with its view of the unique- 

 ness of this world of ours, so far as organic life and humanity are 

 concerned. Yet none the less this speculative dream indestructibly 

 persists, or returns, of something in principle comparable to life, as 

 we know it, having also its place and time within this Universe of 

 Universes, of still but faintly measured vastness, and unknown 

 potentialities. For with such practical infinitude of environment, 

 yet this fundamentally akin in chemical composition and energic 

 processes, and with limitless time, as well as space, for evolution- 

 processes without number, how can we think of our terrestrial life- 

 manifestation as absolutely and permanently unique? Returning, 

 however, to our own earth's companion planets, even though for 

 the presence of life Jupiter be as yet too warm, must he not be 

 cooling down, more or less as the earth has done ? And as for even 

 the farther away planets, with what for earth-life would be too 

 scanty light and heat, who can say but that they may — or may 

 yet — have their success in bearing modes and forms of life com- 

 parable to that of more fully economic green plants, i.e. economic 

 in the above sense, for chlorophyllian plants, than are ours? Or 

 may nearer planets be or become in some way better veiled, or with 

 life-mode less economic of what for our life-forms would be excessive 

 light and heat ? 



After all, our terrestrial and organic Life as we know it needs 

 our very definite physical conditions for its existence, and these are 

 not elsewhere discovered. So what more can be said? What field, 

 even for speculation, remains, save that in so far as other planets, 

 in course of astronomic and geologic time, may conceivably more or 

 less arrive at such viable conditions also ? 



Yet at least one other field remains open to speculation. Recall 

 how though our visible spectrum is but of a single octave among the 

 sixty-two we now recognise, and can even so far create and control, 

 we also know that other forms of organic life can visually appreciate 

 rays of wave-lengths beyond ours on either hand; and similarly for 



