Working naturalists postulate evolution. Zoölogical research is largely directed to the discovery of the genetic relations of animals. The evolution of the animal kingdom is along multifarious lines and by diverse specializations. The particular line which connects man with the lowest forms, through long successions of intermediate forms, is a problem of great interest. This special investigation has to deal chiefly with relations of structure. From the many facts already recorded, it is probable that many detached portions of this line can be drawn, and such a construction, though in fact it may not be correct in all its parts, yet serves a valuable purpose in organizing and directing research.
The truth or error of such hypothetic genealogy in no way affects the validity of the doctrines of evolution in the minds of scientific men, but on the other hand the value of the tentative theory is brought to final judgment under the laws of evolution.
It would be vain to claim that the course of zoölogic development is fully understood, or even that all of its most important factors are known. So the discovery of facts and relations guided by the doctrines of evolution reacts upon these doctrines, verifying, modifying, and enlarging them. Thus it is that while the doctrines lead the way to new fields of discovery, the new discoveries lead again to new doctrines. Increased knowledge widens philosophy; wider philosophy increases knowledge.
It is the test of true philosophy that it leads to the discovery of facts, and facts themselves can only be known as such; that is, can only be properly discerned and discriminated by being relegated to their places in philosophy. The whole progress of science depends primarily upon this relation between knowledge and philosophy.
In the earlier history of mankind philosophy was the product of subjective reasoning, giving mythologies and metaphysics. When it was discovered that the whole structure of philosophy was without foundation, a new order of procedure was recommended—the Baconian method. Perception must precede reflection; observation must precede reason. This also was a failure. The earlier gave speculations; the later give a mass of incoherent facts and falsehoods. The error in the earlier philosophy was not in the order of procedure between perception and reflection, but in the method, it being subjective instead of objective. The method of reasoning in scientific philosophy is purely objective; the method of reasoning in mythology and metaphysics is subjective.
The difference between man and the animals most nearly related to him in structure is great. The connecting forms are no longer extant. This subject of research, therefore, belongs to the paleontologists rather than the ethnologists. The biological facts are embraced in the geological record, and this record up to the present time has yielded but scant materials to serve in its solution.
It is known that man, highly differentiated from lower animals in morphologic characteristics, existed in early Quaternary and perhaps in Pliocene times, and here the discovered record ends.