240 



SCIENCE 



[N. S. Vol. LIV. No. 1394 



on earth it has occurred probably but once 

 during the aeons of geologic time. The mar- 

 velous complexity of the fundamental sub- 

 stance of life, so complex even in its simplest 

 forms that his most precise and elaborate 

 methods of analysis give him but a partial 

 and tentative comprehension of its real struc- 

 ture, must needs strengthen his concept of 

 the immense complexity of the conditions 

 necessary to its creation and evolution. If 

 these conditions have not been duplicated on 

 earth during the whole of the recorded his- 

 tory of life from the Cambrian down to the 

 present day, it appears to him infinitely less 

 probable that they have been duplicated else- 

 where than on the earth. 



That the " man in the street " should be 

 sympathetic with the astronomer's rather than 

 the biologist's conclusion is natural enough. 

 The physical probabilities are obvious enough 

 to all; the complexity of life and its condi- 

 tions he does not realize; nor does he sense 

 the minute relative proportion of time during 

 which intelligent life has existed upon earth, 

 or the vast and impassable barriers of space 

 that preclude the transfer of organized matter 

 from star to star. Moreover, to admit the 

 probability of extra-mundane life opens the 

 way for all sorts of fascinating speculation in 

 which a man of imaginative temperament 

 may revel free from the checks and barriers 

 of earthly realities. 



Such life, if it exists, would surely be 

 evolved ah initio on independent lines of 

 adaptation and the probabilities would be 

 overwhelming that the results of the aeons of 

 its evolution, if by some rare chance it de- 

 veloped intelligent life simultaneously with 

 its appearance on the earth, would be a phys- 

 ical and intellectual type so different funda- 

 mentally from our own as to be altogether 

 incomprehensible to us even if we recognized 

 it as being intelligence or life at all. Who 

 that has studied the ant or the bee has failed 

 to be impressed with the unplumbed mysteries 

 in its sensations, its psychology, its inner 

 life! We are far from any full understanding 

 of the intelligence, if I may use the word, of 

 the social insects, relatives, albeit distant rela- 



tives, of our own, brought up under the identi- 

 cal environment of terrestrial conditions. How 

 much farther would we be from any compre- 

 hension of the intellectual processes of a race 

 of beings whose ultimate origin was wholly 

 different from ours, whose evolution was shaped 

 under conditions that, however closely paral- 

 lel, could not have been identical with those 

 of the earth. Indeed, if we are to take a 

 receptive attitude in this matter, why limit 

 ourselves to protoplasm as the basis of life? 

 What reason have we to suppose that a self- 

 perpetuating substance, capable of acquiring 

 the heterogeneity of function, the multiple 

 complexity of structural adaptation, the spe- 

 cialization of parts, the elaboration of control 

 and correlation organs, and finally the domi- 

 nance of these last and development of con- 

 scious and intelligent beings, must necessarily 

 be based upon the semi-liquid jelly upon which 

 life, as we know it, is fundamentally based? 

 Other substances, solid, liquid, or even gase- 

 ous, may have similar capacities, may have 

 carried them out under different conditioning 

 laws, to a result equally complex and marvel- 

 ous. We know of nothing of the sort. But 

 would we know of it if it existed, even if it 

 existed upon earth? Would there be any 

 conceivable method of communication, any 

 common ideas, interests, or activities, between 

 such beings and ourselves? It does not ap- 

 pear probable. How much less the probability 

 of communication across the void of inter- 

 planetary space. 



To suppose that parallel evolution could go 

 so far as to produce similar methods of ex- 

 ploiting the earth to those used by civilized 

 man — irrigation canals, cities, or other such 

 phenomena of the immediate present — ^in life 

 evolved independently in different planets — 

 and to produce them at an identical moment 

 in geologic time — would seem to be the result 

 of those limitations of constructive or creative 

 thought which are characteristic of myth and 

 fairy-tale, of the anthropomorphic god, or the 

 animal that thinks and talks like a man. Civ- 

 ilized men cannot form any real concept of 

 intelligent life on Mars save in terms of civil- 

 ized life on earth. Yet, so far as we may judge 



