FACT OF EVOLUTION TO THE PHILOSOPHY OF EVOLUTIONISM 339 



caution, that he is speaking of a " basic fact " of prehistory, not 

 of history, not of physics, nor of chemistry, biology, etc. (ex- 

 cept in the supplementary sense upon which we shall soon 

 elaborate) , Whence comes this general agreement about this 

 prehistoric " fact "? Insofar as any conclusion can be drawn 

 from the evidence and inference proper to prehistory, every 

 reasonable objective doubt has been removed, and the evi- 

 dence has converged with such consistency that a firm, reason- 

 able conviction has been generated in the minds of those who 

 have expertly explored the problem. Le Gros Clark puts it 

 clearly this way: 



It is an interesting question, but one which is not easily answered — 

 just at what point in the gradual accumulation of circumstantial 

 evidence (as we have in evolution) can the latter be accepted as 

 adequate for demonstrating the truth of a proposition.'' Perhaps the 

 most we can say is that, in practice, this point is mainly determined 

 by the multiplicity of independent sources from which this evi- 

 dence is derived; if several lines of argument based upon apparently 

 unrelated data converge on, and mutually support, the same general 

 conclusion, the probability that this conclusion is correct may 

 appear so high as to carry conviction to the mind of the unbiased 

 observer.^^ 



Let it be noted that Olson's " basic fact of evolution," like 

 Dobzhansky's statement quoted earlier, is in the logical order 

 of " probability so high as to carry conviction to the mind of 

 the unbiased observer." Without disparaging the logical quality 

 of the phrase " fact of evolution," it remains in the order of 

 probability , not in the order of certainty. By its very nature, 

 evolutionary theory relies on proof and demonstration, the 

 inferences of which have all or most doubts removed, but do 

 not claim the security that the case could not be otherwise. 

 Indeed, for the scientific prehistorian, he might wonder that 

 anyone would raise the question whether he meant by the " fact 

 of evolution " that it was objectively certain and could not be 

 otherwise. He would insist that his science produced proofs of 



^^ " The Crucial Evidence for Human Evolution," in American Scientist, 47 

 (1959) 299-300. 



