September 16, 1921] 



SCIENCE 



241 



from earth conditions, if life exists at all on 

 Mars, it is a thousand to one that it is not 

 intelligent life, for intelligent life on earth is 

 a phenomenon that has existed for ahout a 

 thousandth part of the geologic record of life. 

 And it is a hundred thousand to one that it is 

 not civilized life, for civilized life has existed 

 at the utmost for a hundredth part of the time 

 that man as such has been on the earth. Could 

 we view the earth from without at any earlier 

 portion of her history, we would by no means 

 conclude that the existence of life must needs 

 involve or culminate in the existence of in- 

 telligent life, still less of civilization. We 

 have no means of knowing whether its ex- 

 istence at the present moment is a transitory 

 episode or the commencement of a new era. 

 But if it be the latter, it is probable that the 

 external evidences of civilization a hundred 

 centuries in the future would be as incom- 

 prehensible to us to-day, as impossible to in- 

 terpret in the light of our present knowledge 

 and customs, as our modern civilization would 

 be to the pithecanthropos or the chimpanzee. 

 Does any one seriously suppose, after consid- 

 ering the trends and progress of the last few 

 centuries, that our descendants a thousand 

 centuries hence will still be growing grain and 

 irrigating fields for human provender? Such 

 primitive expedients in food production will 

 probably be obsolete in a hundredth part of 

 that time. Life on earth at any other moment 

 than the immediate present would not be indi- 

 cated to an outsider by any such evidence as 

 our present civilization might afford. Nor is 

 it in the least probable that life upon another 

 planet would be indicated by such evidence at 

 any stage of its existence, or would have any 

 resemblance to our own sufficient for us to 

 recognize it. 



In sum it appears to me as a paleontologist 

 that 



1. The complex concatenation of circum- 

 stances necessary to bring about the initiation 

 of life has occurred upon earth half a dozen 

 times at most, probably but once, in an en- 

 vironment that has apparently been favorable 

 for a thousand million years. The probability' 

 of its occurring in a substantially similar 



environment upon another planet is so slight 

 as to be practically reducible to a mathematical 

 zero in any particular instance. 



2. The number of solar systems being almost 

 infinite, we might regard the number of such 

 possible favorable environments as amounting 

 practically to infinity. 



3. The resultant of these two considerations 

 is that there is a finite and reasonable chance 

 that life has existed or will exist somewhere 

 else in the universe than on this earth alone. 



4. The probability that intelligent life exists 

 is vastly less, and that anything in the least 

 analogous to our civilization exists at the 

 present time is so slight as to be negligible. 



5. If any life involving the development of 

 self-consciousness, of abstract thought and 

 introspection analogous to the higher intelli- 

 gence of mankind, or the control of environ- 

 ment and utilization of natural resources that 

 we call civilization, should develop indepen- 

 dently upon some other planet out of the 

 preexisting simpler phases of life, it prob- 

 ably — almost surely — would be so remote in 

 its fundamental character and its external 

 manifestations from our own, that we could 

 not interpret or comprehend the external in- 

 dications of its existence, nor even probably 

 observe or recognize them. 



6. In any specific instance, such as other 

 planets of our ovm system, the probabilities 

 of the existence of any kind of life amount 

 to practically zero. The probabilities of an 

 intelligent life upon Mars or Venus or else- 

 where in our system so similar to our own in 

 its character and manifestations as to be in- 

 dicated by irrigation canals, cities, or other 

 manifestations of human civilization, appears 

 to be zero of the second degree. The most 

 that one can allow as a reasonable possibility 

 is that there may be some form of life existing 

 somewhere else in the universe than upon our 

 planet. That we have or shall ever get evi- 

 dence of its existence appears to me practically 

 impossible in the light of present knowledge 

 and limitations. 



W. D. Matthew 

 The American Museum of Natural History 



