have been present in their
common ancestor. Let us take an example of such a common character. The
bony external ear-passage is in general as highly developed in the lower
Eastern monkeys and the anthropoid apes as in man. This character must,
therefore, have already been present in the common primitive form. In
that case it is not easy to understand why the Western monkeys have
not also inherited the character, instead of possessing only a tympanic
ring. But it becomes more intelligible if we assume that forms with a
primitive tympanic ring were the original type, and that from these were
evolved, on the one hand, the existing New World monkeys with persistent
tympanic ring, and on the other an ancestral form common to the lower
Old World monkeys, the anthropoid apes and man. For man shares with
these the character in question, and it is also one of the "unimportant"
characters required by Darwin. Thus we have two divergent lines arising
from the ancestral form, the Western monkeys (Platyrrhine) on the one
hand, and an ancestral form common to the lower Eastern monkeys, the
anthropoid apes, and man, on the other. But considerations similar to
those which showed it to be impossible that man should have developed
from an ancestor common to him and the monkeys, yet outside of and
parallel with these, may be urged also against the likelihood of a
parallel evolution of the lower Eastern monkeys, the anthropoid apes,
and man. The anthropoid apes have in common with man many characters
which are not present in the lower Old World monkeys. These characters
must therefore have been present in the ancestral form common to the
three groups. But here, again, it is difficult to understand why the
lower Eastern monkeys should not also have inherited these characters.
As this is not the case, there remains no alternative but to assume
divergent evolution from an indifferent form. The lower Eastern monkeys
are carrying on the evolution in one direction--I might almost say
towards a blind alley--while anthropoids and men have struck out a
progressive path, at first in common, which explains the many points of
resemblance between them, without regarding man as derived directly
from the anthropoids. Their many striking points of agreement indicate a
common descent, and cannot be explained as phenomena of convergence.

I believe I have shown in the above sketch that a theory which derives
man directly from lower forms without regarding ape