In all the foregoing chapters we have been examining and reviewing facts which bear more or less directly on the origin of man. In this final and brief chapter we propose to knit the various threads of evidence together and see how much we really know and what we merely guess concerning the genealogy and antiquity of man. The reader's first difficulty is—unless he is already familiar with works on geology—to obtain a true perspective of the recent periods of the earth's history. The names of geological epochs—Pleistocene (Quaternary), Pliocene, Miocene, Eocene, may mean little to him. We have to picture those periods from what we know of the present or recent period. The Recent period is regarded as stretching into the past until the glacial or Pleistocene period is reached. We have the most hazy ideas regarding the number of years which have passed since a more temperate climate settled over Europe; by some authorities the number is estimated at 15,000 ; by others at 150,000 years. We shall accept the larger figure as the nearer approximation to the truth and use it as a rough standard for the comparison of past geological periods. Now all through the Recent period we find remains of man modern in type and form ; the evolution and origin of man is therefore to be sought for at an earlier date.
The period in the earth's history which preceded the Recent is known as the Pleistocene. It is characterized by periods of cold with temperate intervals. As regards its duration, it may be estimated at least ten times the length of the Recent period—probably even longer. In this period, too, we know of remains of man—of the type known as Neanderthal man. He is very different from modern man. Indeed, Professor Schwalbe and other competent judges regard Neanderthal man as a special species of man —Homo primigenius—while all modern men belong to the species Homo sapiens! Yet Neanderthal man had a very large, and, as we know from his flint implements, a capable brain. We can thus trace man into the Pleistocene period and through it almost to the beginning of that period, but not quite. The oldest Pleistocene man, whom we know only from a lower jaw found in strata near Heidelberg, is also of the Neanderthal type. We do not know the Heidelberg man's skull and brain, but have reason to suppose that both were highly developed. The Heidelberg man belongs to an early stage of the Pleistocene period, but there is evidence to show that man was evolved before this period dawned, for flint implements, of human workmanship, are found in strata formed long before the beginning of the Pleistocene period.
When we pass beyond the Pleistocene we enter the Pliocene period of the earth's history. This is a much longer epoch than the Pleistocene ; it is three or four times as long. Now, we know of no human remains which we can assign to this period with certainty, but it is very probable that the fossil remains found in Java, and ascribed to a human form to which the name of Pithecanthropus has been given, belong to the close of the Pliocene period. Many regard the stratum in which Pithecanthropus was found as having been laid down in the beginning of the Pleistocene period. His small brain and primitive skull indicate a much earlier period—probably Pliocene and not a very late part of that period. Thus, when we enter the Pliocene period we lose all certain trace of man. Some day remains will be found which will carry human history further into the past, but we must stop at this point now and take up the evidence from another point of view.
The Pliocene period we have seen was a long one—three or four times the length of the Pleistocene. The period which preceded the Pliocene—the Miocene—was longer still and the earlier period—the Eocene—still longer. Now we know the Eocene period was the one in which the mammalian forms of life came to the front amongst the types of vertebrate animals. The lowest forms of primates were represented then. At the beginning of the Miocene period the primates had made great progress. We have reason to believe that by the beginning of that period ancestral forms of the monkeys of the New World, of the Old World, and what is much more important to the student of human origin—the ancestral stock of the gibbons or small anthropoids had appeared. By the middle of the Miocene period we find fossil remains of Dryopithecus—the earliest form of the large anthropoids yet discovered. Now that is an important fact; by the middle of the Miocene period a large form of anthropoid had appeared for certain; it may have been evolved earlier. We can say with confidence from the evidence produced in former chapters of this book, that with the appearance of the great anthropoids the point in time is reached when we may reasonably expect the evolution of a human stock. The giant or great-bodied primates probably divided about this period into an arboreal and a terrestrial stock. The arboreal stock gave origin to the gorilla, the chimpanzee, the orang and the extinct ape, Paleopithecus, which we know to have lived in India during the Pliocene period; the terrestrial stock provided the ancestry of man.
Thus we can trace man back to the end of the Pliocene period, and there his traces are lost; we can trace the primate stock forward from the Eocene to the middle of the Miocene, when we see a form which indicates we have reached the point at which the human stock should branch off. From the middle of the Miocene to the end of the Pliocene is as yet a blank in the history of man, but who, on surveying the progress of the last twenty years, will say that this blank will not yet be made good ?