ably the most generalized mammal known." They had five toes on each foot and a bunodont dentition; with primitive ungulate characters went complete sets of unmodified teeth and foot bones.
Marsh's famous pedigree of the horse illustrates the same process. 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 unverifiable, because it is not known where to look for the evidence. Such unverified deductions are frequently scouted as absolutely worthless for the purposes of biological science. This attitude is not taken toward similar 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 deduction that man is descended from lower animals is based are derived from anatomy and embryology. The evidence is circumstantial; but one of the most brilliant of the predictions enumerated was based on this deduction and verified by embryology. It is only with respect to the paleontological evidence that the "deduction 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 circumstantial 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.