Fleischmann then proceeds to point out that when the evidence from other
parts of the anatomy is taken into account, it becomes evident that all
the known fossil remains of horses cannot be arranged in a single line,
but that there are at least three families or groups recognizable. Many
of these forms are known only from fragments of their skeletons—a few
teeth, for instance, in the case of Merohippus, which on this evidence
alone has been placed at the uniting point of two series. At present
about eight different species of living horses are recognized by
zoologists, and paleontological evidence shows only that many other
species have been in existence, and that even three- and one-toed forms
lived together at the same time.
Fleischmann also enters a protest against the ordinary arrangement of
the fossil genera Eo-, Oro-, Meso-, Merohippus in a series, for these
names stand not for single species, but for groups containing no less
than six species under Protohippus, fourteen under Equus, twelve under
Mesohippus, and twenty under Hipparion. Fleischmann concludes: “The
descent of the horses has not been made out with the precision of an
accurate proof, and it will require a great deal of work before we get
an exact and thorough knowledge of the fossil forms. What a striking
contrast is found on examination between the actual facts and the crude
hopes of the apostles of the descent theory!...”
In so far as this criticism of Fleischmann’s applies to the difficulties
of determining the past history of the horse, it may be granted that he
has scored a point against those who have pretended that the evidence is
simple and conclusive; but we should not fail to remember that this
difficulty has been felt by paleontologists themselves, who have been
the first to call attention to the complexity of the problem, and to the
difficulties of finding out the actual ancestors of the living
representative of the series. And while we may admit that the early
enthusiasts exaggerated, unintentionally, the importance of the few
forms known to them, and went too far in supposing that they had found
the actual series of ancestors of living horses, yet we need not let
this blind us to the importance of the facts themselves. Despite the
fact that it may be difficult and, perhaps, in most cases, impossible,
to arrange the fossil forms in their relations to one another and to
living forms, yet on an unprejudiced view it will be clear, I think,
that so far as the evidence goes it is in full harmony with the theory
of descent. This is especially evident if we turn our attention to a
part of the subject that is almost entirely ignored by Fleischmann, and
yet is of fundamental importance in judging of the result. The series of
forms beginning with the five-toed horses and ending with those having a
single toe has not been brought together haphazard, as Fleischmann’s
comparison might lead one to suppose, but the five-fingered forms are
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