Pedigree of the Horse

Proceedings of the London Institution (December 4, 1876)

[129] On Monday afternoon the winter course of lectures at the London Institution opened with an account of "some Recent Additions to our Knowledge of the Pedigree of the Horse," by Professor Huxley. The lecturer began by pointing to two large diagrams representing respectively the skeletons of the common horse (Equus caballus) and the Polar bear (Ursus maritimus). In each, as in other animals, there were a skull, a long vertebrated backbone, and a tail, and there were two generally similar pairs of fore and hind legs, articulated into joints. This generic likeness might on a better acquaintance with the two skeletons be followed out in many minuter details. On the other hand, close study brought to light what the unlikeness of the animals in form and habits would lead us to expect, certain not unimportant differences of structure. Compare the flat fore paws of the bear, adapting it for locomotion on the ice, with the forelegs of the horse, who could but slide about helplessly there, but was the best of all animals for bounding and running. Then the bear had five toes, the horse seemingly had but one. But on each side of the single-developed toe of the horse there was a pair of small splints, which are found to be rudimentary toes. Thus we now had one developed toe and two others undeveloped in the horse to place side by side with the five toes of the bear. In like manner, what in the bear clearly appears as radius and pins of the leg seems the fusion of both together in the horse. But clearer knowledge enabled the anatomist to recognize the ulna in the horse's leg, although it was shrivelled to a mere thread of bone. The comparative structure of the two animals as to femur, tibia, fibula, tarsus, radius, ulna, &c. was then illustrated, and the teeth of the two animals–46 in the bear and 44 in the horse–were compared. Bear and horse were both mammals and both constructed on the same general plan, but with significant differences. It was an interesting question as to which particular toe in the bear's foot the horse's single toe answered to. Science decided that it was the bear's middle toe and our own middle finger, and that consequently the pair of splints or rudimentary toes matched the bear's second and fourth respectively. These were solid facts, resting on perfectly safe and sure induction. But the aim of science was to trace things back as far as possible. We must search for the origin of the structure common to these animals. The theory put forth to explain the matter was that of development by natural selection and survival of the fittest. These variants were held to have all descended from a common ancestry. He thought he had now further evidence of a most interesting and important kind in corroboration of a former thesis. On the wall was a diagram representing the fore-leg, forearm, and teeth of the horse belonging to the Pleiocene and Recent Periods. What must be found was the pair of splints shown as real toes, the small bone of the horse's leg much more distinct from the fibula, the ulna, too, more distinct, and the teeth such as were common to the generality of animals. Seven years back we had plenty of evidence, as we had now, for the structure of the horse in caves of the Glacial epoch and of that next before it. Moreover, in the older strata of the Upper Meiocene there were remains of an animal wonderfully like the horse, though with striking differences as to teeth and limbs. He referred to the Hipparion. Here the two splints were really three-jointed toes, and the tibia and ulna were sensibly distinct from one another. Nay, in the Lower Meiocene strata of France, Germany, and the Unites States there had been discovered the remains of an animal now known as the Anchitherium; also a real horse, although differing as much from the Hipparion as the Hipparion did from the horse of recent period. This animal not only showed the three toes, but walked on them. The fibula was complete throughout, and was firmly fastened to the tibia by a distinct ligature. The ulna and the teeth sensibly approached the normal type. This evidence struck him forcibly six or seven years ago. It was even then not only a tenable, but also a probable hypothesis that the horse was but the last term of a series of which the Anchitherium was the first then known and the Hipparion the middle term. But now a mass of fresh and invaluable facts had some to them from an unexpected quarter. Between the Mississippi and the Rocky Mountains, that vast and little known region known as "the Bad Land," geological diggings had been recently yielding up their treasures. In the Tertiary Period this country was an enormous lake, in the mid of which during untold ages its fauna had been imbedded. This vast catacomb of rock was thousands of feet in depth, and was full of organic remains. They not only filled up an immense gap in the record of geological time, but furnished most important missing links that had been hitherto wanting in the "Pedigree of the Horse." In the Meiocene Professor Marsh had found an animal very like the Anchiterium, although the resemblance was far from exact. This Professor Marsh had named the Meiohippus. In older strata will he had found another intermediary form, the Mesohippus. Lastly, in the Eocene, or the oldest bed of the Tertiary system, the Orohippus, which was a little animal of the horse kind, no bigger than a fox, but interesting on account of the wonderful verification it afforded to scientific forecast. This oldest known type of the horse kind had four complete toes on each fore foot, although it has no more than three to each hinder leg. In the recent strata was found the common horse; in the Pleiocene, the Pleiohippus and the Protohippus or Hipparion; in the Meiocene, the Meiohippus, or Anchitherium, and the Mesohippus; and in the eocene, the Orohippus. These were all compared with reference to fore feet, hind feet, fore arm, leg, teeth. Professor Huxley said he thought this chain of ascertained facts verified so far the doctrine of evolution, and justified him in saying he should not in future take the trouble to discuss that doctrine on a priori grounds. There was no longer any other reasonable and fair hypothesis and it might truly be called an ascertained fact that the various forms of the horse kind were all descended from a common ancestry. Just as certainly as there was a point whence the horse and the bear diverged, so there must have been a common point whence all mammals diverged.


C. Blinderman & D. Joyce
Clark University