390 THE POPULAR SCIENCE MONTHLY. 



ably the most generalized mammal known." They had five toes 

 on each foot and a bnnodont dentition ; with primitive ungu- 

 late characters went complete sets of unmodified teeth and foot 

 hones.* 



Marsh's famous pedigree of the horse illustrates the same pro- 

 cess. Both he and others clearly foresaw many of the results 

 that he afterward worked out. A large part of the logical value 

 of this restoration of the genealogy of the horse family arises 

 from the fact that what is now established by investigation was 

 once an unverified deduction.! 



Such verifications, especially in paleontology, are often due to 

 accident. The predictions might, therefore, and often actually 

 do remain unverified and practically un verifiable, because it is not 

 known where to look for the evidence. Such unverified deduc- 

 tions are frequently scouted as absolutely worthless for the pur- 

 poses of biological science. This attitude is not taken toward simi- 

 lar deductions in other sciences, for the single reason that there 

 are no external reasons for combating the theories. Enumerating 

 a number of such cases from physics and chemistry, Jevons adds, 

 " To my mind, some of the most interesting truths in the whole 

 range of science are those which have not been, and in many 

 cases probably never can be, verified by trial." % 



The most famous of these unverified deductions in biology is 

 that concerning the descent of man. The facts on which the de- 

 duction that man is descended from lower animals is based are 

 derived from anatomy and embryology. The evidence is circum- 

 stantial; but one of the most brilliant of the predictions enumer- 

 ated was based on this deduction and verified by embryology. It 

 is only with respect to the paleontological evidence that the " de- 

 duction is unverified/' But if the chain of missing links were 

 absolutely complete, it would only be circumstantial evidence. 

 The direct evidence is forever beyond reach, because when the 

 race was born there was no scientist present to observe it. 



This case serves well to illustrate the nature of the objections 

 to the theory. The best theory of evidence of a historical nature 

 has been worked out by the law courts. There, no amount of 

 negative evidence has any value whatever in the face of even cir- 

 cumstantial evidence of a positive nature. The only way in 

 which the accused one can shake off the implication is, to furnish 

 positive evidence that some one else committed the crime, or 

 that he was in some other definite place when it was committed. 

 A careful consideration of the well-understood doctrine of alibi, 



* Cope, American Naturalist, August, 1884. 



\ Marsh, American Journal of Science, March, 1874, and other papers in the same 

 journal. \ Principles of Science, p. 548. 



