Mad about Science: Horses

By Brenden Bobby
Reader Columnist

Dogs have earned the moniker of “man’s best friend,” but it may be more accurate to relabel them as “man’s oldest friend.” Dogs were domesticated around 14,500 years ago, becoming the first willing animal companions to humankind. However, horses, though domesticated sometime around 2200 B.C.E., have proven themselves among the most capable and empathetic animals humans could ask for.

Among all domesticated animals, horses are some of the most recent, albeit most useful, to humans. They have vastly increased human mobility, serving as the primary mode of transportation over land until the invention of the steam engine, the locomotive and the automobile.

Thoroughbred horses are capable of running at sustained speeds of 45 miles per hour. Some horses were specifically bred to run, though the species as a whole comes with a number of genetic benefits that make them exceptional runners. The first and most obvious is the presence of four legs over a human’s two. However, as the tortoise has shown us, four legs are not universally better than two — instead, it’s everything supporting the legs that makes a horse great at running.

Horses are very muscular and have a strong cardiovascular system, even for their size. Paired with their ability to breathe exclusively through their nose, this gives them an immense amount of oxygen to circulate in their bloodstream, which helps fuel every aspect of their body, from the specialized springy tendons to the huge muscles in their legs.

Another unique adaptation is the presence of hooves. Ungulates such as horses and deer essentially run on their tippy-toes. This would be wildly impractical for humans because of the way our bones are arranged and the amount of weight we can put onto our toes — even highly trained ballerinas are prone to breaking their phalanges during performances and training. A horse’s hoof encases the end of its toe — essentially making it a big toenail — providing a strong foundation and structure, while also allowing the toe and the bones that make up its foot to elongate its leg. This helps horses have a much longer stride and withstand the immense forces their legs must carry.

This is also why owners often kill horses when they break a leg. Horses live on their feet, and if the leg won’t heal, the horse won’t live a very pleasant life and may even be prone to re-breaking its leg. When someone decides to euthanize their horse after an injury, it’s not just a matter of cost, but a consideration for the horse’s quality of life in the long-term.

Having broken a leg, I can tell you that the way humans evolved is much more conducive to healing a broken limb. If I had to keep walking on a compound fracture, I’d never be the same, but I would also have the ability to live a more decent life as an amputee than an animal that requires all four limbs to move.

Like all animals, horses have a long and complicated evolutionary history. One of the horse’s earliest known ancestors is Eohippus, or the “dawn horse.” It was a strange little creature that existed 55 million years ago and was about the size of a dog. It had four toes on each front foot and three toes on each rear foot, with every toe ending in a small hoof. Even stranger, Eohippus had very pronounced, sharp canine teeth, which is a massive departure from the modern equus.

Every aspect of a horse’s evolution occurred in conjunction with its environment. The multiple, spread toes worked well in moist, primeval forest environments where a solid grip was required to survive. As Earth’s temperature changed and grasses began to proliferate around the globe, these multiple toes began to coalesce into a single toe and hoof. The shape of horses’ teeth also changed to shear and consume grass, and they became bigger and faster to evade predators.

Horses today are peak herbivores. They have very few natural predators, especially when they are being cared for by humans. Wild horses are sometimes vulnerable to predation by large carnivores such as mountain lions and wolves. Mountain lions in the American West have been found to ambush wild horses, though this behavior is somewhat rare due to the danger posed to the mountain lions. Wolves are more likely to prey upon wild horses by attacking from multiple vectors and isolating a horse in terrain favorable for the pack.

Foals are the most vulnerable to predators and are often targeted by mountain lions, coyotes and bears. Adults are fully capable of defending themselves, as they are able to deliver up to 1 metric ton of force per square inch with a single kick — more than double the force of the most powerful heavyweight boxers. That amount of force can easily break human bones, cause a concussion or skull fracture and dent car doors.

Throughout most of their domestication, horses have been used for combat. In antiquity and the medieval period, horses were seen as an immense investment — they were essentially the main battle tanks of the age. Knights and lords wanted their investments protected, so they armored them up. Barding — body armor for war-horses — came in many forms, from light to full-blown Milanese plate mail. A horse lost in combat could end a very carefully curated bloodline, both for the horse and its rider, which made the armor as valuable and complex as the beast it shielded.

Stay curious, 7B.