The facts of anatomy, physiology, and embryology, of which we have given
illustrations, all point to man's affiliation with the order of monkeys
and apes. To this order is given the name Primates, and our first and
second question must be when and whence the Primates began. The rock
record answers the first question: the Primates emerged about the dawn
of the Eocene era, when grass was beginning to cover the earth with a
garment. Their ancestral home was in the north in both hemispheres, and
then they migrated to Africa, India, Malay, and South America. In North
America the Primates soon became extinct, and the same thing happened
later on in Europe. In this case, however, there was a repeopling from
the South (in the Lower Miocene) and then a second extinction (in the
Upper Pliocene) before man appeared. There is considerable evidence in
support of Professor R. S. Lull's conclusion, that in Southern Asia,
Africa, and South America the evolution of Primates was continuous since
the first great southward migration, and there is, of course, an
abundant modern representation of Primates in these regions to-day.
As to the second question: Whence the Primates sprang, the answer must
be more conjectural. But it is a reasonable view that Carnivores and
Primates sprang from a common Insectivore stock, the one order diverging
towards flesh-eating and hunting on the ground, the other order
diverging towards fruit-eating and arboreal habits. There is no doubt
that the Insectivores (including shrews, tree-shrews, hedgehog, mole,
and the like) were very plastic and progressive mammals.
What followed in the course of ages was the divergence of branch after
branch from the main Primate stem. First there diverged the South
American monkeys on a line of their own, and then the Old World monkeys,
such as the macaques and baboons. Ages passed and the main stems gave
off (in the Oligocene period) the branch now represented by the small
anthropoid apes--the gibbon and the siamang. Distinctly later there
diverged the branch of the large anthropoid apes--the gorilla, the
chimpanzee, and the orang. That left a generalised humanoid stock
separated off from all monkeys and apes, and including the immediate
precursors of man. When this sifting out of a generalised humanoid stock
took place remains very uncertain, some authorities referring it to the
Miocene, others to the early Pliocene. Some would estimate its date at
half a million years ago, others at two millions! The fact is that
questions of chronology do not as yet admit of scientific statement.
[Illustration: SIDE-VIEW OF SKULL OF MAN (M) AND GORILLA (G)
Notice in the gorilla's skull the protrusive face region, the big
eyebrow ridges, the much less domed cranial cavity, the massive lower
jaw, the big canine teeth. Notice in man's skull the well-developed
forehead, the domed and spacious cranial cavity, the absence of any
snout, the chin process, and many other marked differences separating
the human skull from the ape's.]
[Illustration: THE SKULL AND BRAIN-CASE OF PITHECANTHROPUS, THE JAVA
APE-MAN, AS RESTORED. BY J. H. McGREGOR FROM THE SCANTY REMAINS
The restoration shows the low, retreating forehead and the prominent
eyebrow ridges.]
[Illustration: SUGGESTED GENEALOGICAL TREE OF MAN AND ANTHROPOID APES
From Sir Arthur Keith; the lettering to the right has been slightly
simplified.]
We are on firmer, though still uncertain, ground when we state the
probability that it was in Asia that the precursors of man were
separated off from monkeys and apes, and began to be terrestrial rather
than arboreal. Professor Lull points out that Asia is nearest to the
oldest known human remains (in Java), and that Asia was the seat of the
most ancient civilisations and the original home of many domesticated
animals and cultivated plants. The probability is that the cradle of the
human race was in Asia.