Do Horse Toes Support Evolution?

The loss of horse-hoofed toes:
scientists baffled about why they
were lost. But were they?

 

by Jerry Bergman, PhD

The ‘horse series’ icon of evolution has been one of the most commonly cited “proofs” of evolution for over 150 years.[1] Its importance is illustrated by the fact that “apart from human evolution, horse evolution represents the only “classic” example [of the evolution of] mammals.”[2] Furthermore, the evidence for the horse’s alleged development through supposed evolutionary time has been primarily based on a reduction in the number of its toes, so the

traditional story of the evolution of the horse (family Equidae) has been in large part about the evolution of their feet. How did modern horses come to have a single toe (digit III), with the hoof bearing a characteristic V-shaped keratinous frog on the sole, and what happened to the other digits?[3]

Aside from size, from small to large, one of the changes often used to document horse evolution is this presumed change of its toe digits from four to the single toe called a hoof. The proposed early horse ancestor, Hyracotherium, often called Eohippus, the ‘Dawn Horse’ of the Eocene Epoch, had four front toes like the modern tapir, compared to the modern horse which has only a hoof.[4] Thus, the horse lineage exhibits the most extreme digit reduction known, from four metacarpals to one, resulting in the monodactyl forelimb of Equus.

This important change was not the evolution of a new trait, as required by evolution, but the loss of its four side digits. New research has documented that they were not lost, but are now vestigial. Specifically, the proximal portions of digits II and IV were retained as splint bones and the distal portion was retained as part of the frog. The frog is a tough, thick, V-shaped structure pointing down from the heels which functions to protect the digital cushion beneath it. It also acts as a shock absorber when the horse moves, and aids in both traction and blood circulation in the hoof.  The researchers, by an analysis of the animal’s osteology, joint articulations, and nerve and vessel distribution within the distal forelimb, theorized that “the Equus manus maintains remnants of the ‘missing’ digits. While it is already known that digits II and IV persist proximally as the splint metacarpals, we propose that digits I and V are also present proximally and that components of all five digits are found distally within the manus.”[5]

Solounias et al., believes that all four digits are partially present in the modern adult forelimb. They also noted that, although “Digit reduction is common among mammals…  The horse lineage exhibits the most extreme digit reduction, resulting in the monodactyl” design.[6] Furthermore, anatomical and embryological evidence exists for the proximal portions of all the accessory digits (i.e., I and V, as well as II and IV) being retained in the feet of modern horses.[7]

They concluded that

the evolutionary change to monodactyly is not as dramatic as previously thought and that the horse forelimb is more similar to that of its pentadactyl, tetradactyl and tridactyl ancestors. Although the modern horse maintains only one complete digit, the identities of all five digits are preserved in both the skeletal and soft anatomy as embedded elements into the dominant digit, and the digit positions are consistent with horses in earlier stages of evolution.[8]

Other paleontologists have marshaled evidence rejecting this conclusion in the 2018 paper published in the journal Royal Society Open Science. They, instead, supported the theory that these toes were completely lost in evolution[9] and were not retained within the hoof as proposed by Solounias et al.[10] These detractors based their conclusions on their evaluations of the osteology and metacarpal articulations of the horse and several extinct equids using specimens from the American Museum of Natural History, Yale Peabody Museum, and the Museum of Comparative Zoology at Harvard. Their evaluations supported the position that the distant ancestors of modern horses had multiple hoofed toes which over time were completely lost—leaving the singular hoof existing in modern horses. The advantages of the monodactyly design were detailed by Solounias et al. as follows:

The reduction of digits in the horse is accompanied by an increase in overall limb length, therefore increasing the distance of each stride. Monodactyly evolves to allow the trot gait characteristic of the modern horse. The limb adapted for the faster trot gait facilitates locomotion in the grassland habitat, as horses are known grazers. The horse limb evolved to move primarily in flexion and extension, and the overall limb structure prevents supination and pronation. In addition, the simplification of the horse hand into a single complete digit stabilizes the limb by reducing the total number of joints.[11]

Solounias et al., concluded that

Although the modern horse maintains only one complete digit, the identities of all five digits are preserved in both the skeletal and soft anatomy as embedded elements into the dominant digit, and the digit positions are consistent with horses in earlier stages of evolution.[12]

The Extinction Theory

Another position is that the Eocene Hyracotherium was not an extinct horse as commonly assumed by evolutionists. Rather it was an extinct animal that had feet like those of a modern tapir: four toes in front and three behind.[13] Each toe was individually hooved with an underlying foot pad. The extinction theory is supported by the fact that the equid fossil record includes an estimated 50 genera and hundreds of species and the extinct Eocene Hyracotherium. Thus the oldest known horse from this view was just another extinct horse-like animal.[14] The estimated 50 genera and hundreds of species enables evolutionists with enough examples to select ones that present the picture of straight line evolution.

Many enormous differences exist between a modern horse and the Eocene Hyracotherium, including body size. The Hyracotherium was about the size of a house cat, requiring massive changes to evolve to the size of a modern horse. These changes include going from the size of a house cat to an animal between 1.5 and 2 meters tall, with an average weight of from 900 to 2,000 pounds (450 to 1200 kg).[15]  This weight difference requires a very different bone design than possessed by a house cat.[16] Another difference between modern horses and Hyracotherium was that Hyracotherium had a primitive short face with eye sockets closer to the middle of the face as compared to a horse, which has eyes more on the sides of the head. There is also a shorter distance between its front teeth and the cheek teeth than that found in a horse.

Paleontologists have many examples to guide them in determining Hyracotherium  traits because Hyracotherium fossils have been found at many localities in both the western U. S. and Europe. Furthermore, the evolution of equids has been studied extensively.[17] Unfortunately, evolutionary presuppositions dominate the interpretation of the fossil record. An example of where evolution has been assumed is the following claim: “As the taxa evolved, the forefoot (manus) changed from being tetradactyl to tridactyl and ultimately becoming monodactyl”[18] If evolution was not assumed, these differences could be explained as design variations between different animals. That would be more logical.

Another example where evolution belief dominates is in the statement that modern horses “have a single hoof, but their distant ancestors actually had five toes. Researchers say that the hooved toes vanished over time, thanks to evolution.” Modern equids, such as horses, asses, and zebras, have only a single toe, the “left-over original third toe” on each foot, encased in a thick-walled keratinous hoof, with an underlying triangular ‘frog’ on the sole that acts as a shock absorber.

Summary

Evolutionists admit that they have no consensus on the question of why modern horses lost toes. As described by Darwinists such as Brianna McHorse, who said, “Horses are a classic example of macroevolution in three major traits—large body size, tall-crowned teeth (hypsodonty), and a single toe (monodactyly)—but how and why monodactyly evolved is still poorly understood.”[19] Clearly, as one article headline in Popular Science proclaimed, the loss of four toes is a mystery.[20] As these quotes indicate, explanations are often driven by an evolutionary ideology and other options are not seriously considered. Other options include the idea that a wide variety of “horses” once existed, some with several digits, and some which later became extinct. One of these varieties that survived had four front toes, like species in the modern tapir family.

Another theory is the vestigial claim, wherein horses once had 5 toes but lost 4 of them, a view which does not support evolution, but the degeneration theory. Yet another theory is that the 4 toes once thought lost in the modern horse actually still exist in vestigial form, another version of the vestigial theory. The fact that the modern horse hoof provides several advantages supports the view that a variety of designs existed in the past, and horses with multiple digits became extinct for the same reason(s) why many animals have become extinct. Thus the only horse hoof pattern still surviving today is the monodactyly design.

—Ed. note: and it works very well, considering the history of horses in battle, in law enforcement, and in sport.

References

[1] Janis, Christine. “The Horse Series,” pp. 251-280 in Icons of Evolution: An Encyclopedia of People, Evidence, and Controversies (edited by Brian Regal, 2007). Westport, CN: Greenwood Press,  p. 251, 2008.

[2] Christine, 2008.

[3] Vincelette, Alan R. 2023. Hipparion tracks and horses’ toes: The evolution of the equid single hoof. Royal Science Open Science 10(6):230358; https://royalsocietypublishing.org/doi/full/10.1098/rsos.230358, 2008.

[4] Vincelette, 2023.

[5] Solounias, Nikos, et al. The evolution and anatomy of the horse manus with an emphasis on digit reduction. Royal Society Open Science 5(1):171782; https://royalsocietypublishing.org/doi/10.1098/rsos.171782, 24 January 2018.

[6] Solounias, et al., 2018.

[7] Solounias, et al., 2018.

[8] Solounias, et al., 2018.

[9] Vincelette, 2023.

[10] Solounias, et al., 2018.

[11] Solounias, et al., 2018.

[12] Solounias, et al., 2018.

[13]Waugh, Rob. Horses ‘used to have toes’, new study shows. yahoo!news; https://www.yahoo.com/news/horses-used-to-have-toes-new-study shows120714112.html, 21 June 2023.

[14] McHorse, Brianna K., et al. The Evolution of a Single Toe in Horses: Causes, Consequences, and the Way Forward. Integrative & Comparative Biology. 59(3):638-655, p. 638, 24 May 2019.

[15] Floyd, Andrea E. “Evolution of the Equine Digit and Its Relevance to the Modern Horse.” Chapter 7 in Equine Podiatry (eds. A.E. Floyd and R.A. Mansmann), pp. 102-111. W.B. Saunders Company, New York, NY (Elsevier, Health Sciences Division, St. Louis, MO), p. 102, 2007.

[16] McHorse, et al., 2019, p. 638.

[17] Solounias, Nikos et al. 2018

[18] Solounias, Nikos et al. 2018

[19] McHorse, Brianna. 2019. Integrative and Comparative Biology. The Evolution of a Single Toe in Horses: Causes, Consequences, and the Way Forward. 59(3) :638-655.

[20] Baisas, Laura. Horses once had multiple hoofed toes. What happened to them is still a bit of a mystery. Popular Science, 21 June 2023.

[21] Clark, C.S. God or Gorilla: Images of Evolution in the Jazz Age. Johns Hopkins University Press, Baltimore, Maryland, pp. 28, 45, 2008.

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Dr. Jerry Bergman has taught biology, genetics, chemistry, biochemistry, anthropology, geology, and microbiology for over 40 years at several colleges and universities including Bowling Green State University, Medical College of Ohio where he was a research associate in experimental pathology, and The University of Toledo. He is a graduate of the Medical College of Ohio, Wayne State University in Detroit, the University of Toledo, and Bowling Green State University. He has over 1,300 publications in 12 languages and 40 books and monographs. His books and textbooks that include chapters that he authored are in over 1,800 college libraries in 27 countries. So far over 80,000 copies of the 60 books and monographs that he has authored or co-authored are in print. For more articles by Dr Bergman, see his Author Profile.