erged from the common ancestral form before the
existing types of anthropoid apes had diverged from each other.
Now this divergence almost certainly took place as early as the
Miocene period, because in the Upper Miocene deposits of
western Europe remains of two species of ape have been found
allied to the gibbons, one of them, dryopithecus, nearly as
large as a man, and believed by M. Lartet to have approached
man in its dentition more than the existing apes. We seem
hardly, therefore, to have reached in the Upper Miocene the
epoch of the common ancestor of man and the anthropoids."
(_Darwinism_, p. 455, London, 1889.) Mr. Wallace goes on to
answer the objection of Professor Boyd Dawkins, "that man did
not probably exist in Pliocene times, because almost all the
known mammalia of that epoch are distinct species from those
now living on the earth, and that the same changes of the
environment which led to the modification of other mammalian
species would also have led to a change in man." This argument,
at first sight apparently formidable, quite overlooks the fact
that in the evolution of man there came a point after which
variations in his intelligence were seized upon more and more
exclusively by natural selection, to the comparative neglect of
physical variations. After that point man changed but little in
physical characteristics, except in size and complexity of
brain. This is the theorem first propounded by Mr. Wallace in
the _Anthropological Review_, May, 1864; restated in his
_Contributions to Natural Selection_, chap. ix., in 1870; and
further extended and developed by me in connection with the
theory of man's origin first suggested in my lectures at
Harvard in 1871, and worked out in _Cosmic Philosophy_, part
ii., chapters xvi., xxi., xxii.]

[Sidenote: Pleistocene men and mammals.]

Whatever may be the final outcome of the Calaveras controversy, there
can be no doubt as to the existence of man in North America far back in
early Pleistocene times. The men of the River-drift, who long dwelt in
western Europe during the milder intervals of the Glacial period, but
seem to have become extinct toward the end of it, are well known to
palaeontologists through