Q. Surely you have seen the convincing skeletal evidence for the
evolution of the horse family? How can you dismiss it?
A. Probably the best known of such fossil
sequences is that of early horses discovered mainly in North America.
Illustrations of this sequence figure prominently in textbooks on palaeontology
and in natural history museums around the world. It is due to the passionate
bone collecting of O. C. Marsh, professor of paleontology at Yale University,
and his intense rival Edward Cope. Their materials were arranged by Henry
Fairfield Osborn, director of the American Museum of Natural History.
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One of the principal modern champions of Osborn's
evolutionary sequence for horses was George Simpson professor of palaeontology
at Columbia and Harvard. Simpson himself made important fossil horse discoveries
in Texas in 1924, and his 1951 book, Horses, first encapsulated all the
findings of the American Museum team. The famous chart that every schoolchild
learns came first from Simpson's book.
The chart begins with a tiny creature the size of a dog, poetically named
Eohippus (dawn horse) by Marsh, with teeth suited to forest browsing. In beds of
Oligocene age are found the remains of Mesohippus, a creature the size of a
sheep. In Miocene beds are found fossils of Merychippus whose teeth are adapted
to grass-feeding habits. And from Pliocene beds come the remains of Dinohippus,
an animal the size of a small pony with teeth fully adapted to grazing.
There is no question that these remains, when
placed together, are strongly suggestive of an evolutionary development. They
show what the evolutionary model predicts the fossil record should show. In fact
it is comparative anatomy of this sort that provides the strongest body of
evidence for evolution in the first place. And it is easy to understand the
enthusiasm and speed with which the American Museum set up its display - a
display rapidly copied by the British and other museums.
From a purely scientific standpoint, however,
there are three problems with this sequence. The first is that although the
fossil record has been bountiful enough to provide these intermittent remains,
it has been consistently reluctant to yield up any remains that are actually
transitional between them. The similarities between Eohippus and Mesohippus are
great. But their differences are greater still. Bones of Eohippus and bones of
Mesohippus have been found in a number of places. But bones of the animals that
are said to connect them in lineal descent are not merely rare - they are
nonexistent.
The second problem is that, given the continued
existence of gaps in the fossil record, and the continued failure to find
fossils of the hypothetical intermediate species, then to call the Eohippus
sequence an evolutionary series is not a scientific theory - it is an act of
faith, a matter of belief. It is perfectly true that an intelligent rational
person can examine the remains and be convinced that they represent an
evolutionary sequence, but not by virtue of any evidence that has been adduced,
since the Eohippus sequence is not evidence for evolution. It is evidence
for the former existence of different species of quadruped with a striking
similarity, not evidence of a relationship between them. And it is this, the
relationship -- if any -- that is the very matter in question.
The third problem is that Simpson's famous chart
is actually false is some important respects. It clearly shows an unbroken
evolutionary sequence. Yet Simpson himself admits in his text that there are
gaps. There is a gap right at the beginning of the sequence before Eohippus. And
there is another gap, at the end of the Eocene and before the Oligocene, that is
after Eohippus and before Mesohippus.
We are entitled to ask: what exactly is it that
connects these fossils scientifically?
