What is the closest living relative to equines?

Not cows or pigs.

The two closest living relatives to the horse are the rhinoceros and the tapir. All three animals are part of the perissodactyl group - odd number of toes rather than even numbered.

(Despite the fact that hippopotamus means "river horse," horses are not particularly closely related to hippos).

This close relationship is why some people joke that rhinos are unicorns. (More likely the species that inspired the unicorn legends was a deer or antelope).

Why do horses have one hoof and cows two?

We actually don't really know. We do know that two hooves (like sheep and goats) are better for gripping on really rough terrain.

Single hooves aren't better for speed either - cloven-hooved antelopes run very fast too. It might be that a single hoof is better if you want to be both fast and big (although wild horses are very small compared to domestic horses, they're still bigger than most deer).

Truth is? We don't actually know.

What Are The Three Kinds Of Horse?

Equus caballus is split into three broad types. These types represent different wild populations that were absorbed.

1. The steppe horse. This was the first horse to be domesticated and originated on the Asian steppes. The steppe horse refined into the modern Turkemen and Akhal-teke horses, the Arabians and Barbs of north America, and reaches its ultimate form in the Thoroughbred. The descendants of the steppe horse are refined, light, and very fast. They have fine coats and tend towards sparse manes and tails. They are often called "hotbloods." (Contrary to popular belief, the three founding sires of the Thoroughbred were not all Arabians - at least one was a Turkoman. The purest remnants of the original steppe horse are the Tarpan and the Caspian, although Icelandic horses closely resemble the Tarpan and may also be close to pure "steppe."

A modern American Thoroughbred is "walked out" after a race (it was blistering hot that day).

2. The forest horse. Originating in central Europe, the forest horse is a stocky, heavy horse with much more "hair" on it than the steppe horse. Forest horses have feather over their hooves. The forest horse has been bred up in size. And up. And up. The modern descendants of the forest horse are the various draft breeds, which include the biggest breed of horse in the world - the Shire. Draft horses are also sometimes called coldbloods.

A roan Belgian carries her own harness...she's about to be loaded onto a trailer. This is a fairly small draft horse.

3. The hill horse. Originated in northern Europe. Small, smart, and scrappy, hill horses are tough, survive on minimum forage, but don't breed up in size well at all. Like the forest horse, they tend to have a lot of hair. Actually, they often have even more hair. The modern descendants of the hill horse are all the various pony breeds - tough, often difficult to handle, but easy and cheap to keep.

A Shetland pony in a standing stall. His mane has been trimmed because it gets so hot here - it should be all the way down to the bottom of his neck.

All of our modern breeds of horse, every one, are descended either from one of these three types or from specific interminglings of the two.

Most light horses are "warmbloods" - created by mixing coldblood lines with hotblood ones. This includes the modern American stock horse - the most popular breed of horse in North America is the Quarter Horse - as well as sport horses and the highly refined, carefully bred Warmblood breeds of Europe. (Note that warmblood, small w, can be any light horse, but Warmblood, large w, should only be used to refer to a horse registered with a Warmblood registry).

A Dutch Warmblood stallion doing high level dressage. Source: Fotoimage via Wikimedia Commons.

Draft ponies such as the Haflinger, the British colored cob and its Irish equivalent (often called "gypsy" or "tinker" horses), and the Norwegian Fjord are a mix of coldblood and pony blood.

A classic "draft pony" - the Norwegian Fjord.

Sports ponies are often made by crossing ponies and hotbloods - pony/Thoroughbred crosses are popular in Britain. Some riding pony breeds, such as the modern Welsh Pony, have a fair bit of Thoroughbred in them.

Me riding a pinto sports pony, probably a Paint/Welsh cross. (Yes, I am that short. That is really a pony.

Why Don't We Ride Cows?

City folk tend to see horses and cows as essentially quite similar animals. They're similar in size and they both eat grass.

However, they are quite different in many ways.

Cows (and sheep and goats) are ruminants. They have a four part stomach and they eat each item of food twice. It's partially digested, regurgitated, chewed again and swallowed into a different part of the stomach - a process called "chewing cud". (Rabbits, incidentally, perform the same process by a slightly different mechanism - coprophagy - they produce two kinds of dung, one of which goes through again).

Horses are hind gut fermenters. They have a relatively small stomach and a massive gut, and they handle grass by digesting it for a long time in a large gut that ferments it extensively. (This, by the way, means it is very, very hard to intoxicate a horse, even a small one.)

Cows have cloven or divided hooves. This means they stand on two toes of the original five.

Horses stand on one toe - a single hoof.

These differences are key to our different uses of these animals.

Cows have been used as work animals in the past, because it is easier to create a pulling harness for oxen than for horses. Oxen can pull using a yoke, which is similar to the yokes used to increase the lifting capacity of men. Horses, because of their longer and more flexible necks, can't. But as soon as people come up with a good way to use horses, they mostly stop using oxen.

An ox team pulling using a yoke. Source: Allen Drebert via Wikimedia Commons.

Why?

It comes back to that chewing the cud thing. A cow's digestive system has to stay constantly active. She has to have enough fiber in the rumen (first stomach) for it to stay active and healthy. This means that a cow has to spend at least eight hours a day, every day, chewing cud. If you feed cows high energy feed to reduce the amount of time they spend eating, you can damage their rumen - a balance dairy farmers battle with.

Horses, in the natural state, spend about 20 hours a day grazing. However, you can give a horse high energy feed - grain, carrots, apples - a couple of times a day and reduce that grazing time down to a few hours a day...meaning you can work a horse for 8-10 hours a day and have it stay healthy. It's better for them to spend all day grazing, but they aren't going to get sick off of spending less time eating and more time working alone.

So, you can only realistically work a team of oxen for four hours a day - and you can work a team of horses for eight. Which gets your fields plowed faster?

Hence, we don't ride cows.

Usually.

Because there are exceptions to everything - a rodeo cowboy trying to ride a bull.  Source: Cszmurlo via Wikimedia Commons.

There are also a few people riding and even jumping cows out there. I wasn't able to find a legal-for-use picture, sadly.

Where Did Horses Come From/Evolve?

I'm talking specifically about horses here. The modern horse evolved on the American Great Plains, then crossed the land bridge into Asia.

It then became extinct in the New World (possibly as a result of human hunting). The horses in Siberia and Mongolia fared better and equines (both wild and domesticated) spread outwards from there.

The donkey, on the other hand, originated in north Africa and spread into the Middle East.

It's worth remembering that horses are cold climate animals whilst donkeys and zebras are hot climate ones. Donkeys are a desert animal - hence the ears!