Domestication
The horse was domesticated 4000 years ago. At first for their meat and milk, later to work in agriculture.
Later on they were used for wars. Since then people started with genetically engeneering, so their horses would be better than those of the enemy. Breeds started to develop, for their endurance and strength. This was also the period were saddles and stirrups were invented, tools to brace. The Greek general Xenofon has written the first work about the horse as a tool for the military, and nowadays there are still dressage schools like the Spanish Riding school, which is a remaining product of that idea.
A third reason for domestication was transportation, to deliver mail or food for exemple. Some of these animals escaped, like the mustangs. They're hated by farmers, because their desire to make a herd is so big that they still steel domesticated horses out of their pastures.
If we overlook the history of the horse, it's only been domesticated for a very short period of time....
It doesn't take long to turn a domestic horse back into a wild horse, because they're still very close to their roots.

Survival of the fittest
We all know this law of nature: the one who addapts himself the best to a new situation, survives... There's an everlasting natural selection going on, and only the fastest, cleverest and healthiest creatures survive.

The two teams
In this competition, there are 2 teams: predators and prey animals.
Predators, like a lion or a wolf, are born to kill prey animals: their eyes are close to eachother so they can focus on a prey. They often hunt in groups for convenience, but they'll always try to get the best bite. They want to survive as an individual.
Prey animals are born to not be killed by predators: their eyes are to the side of their head, so they are very well equiped to register every suspicious movement. They move in herds, often with the youngest animals in the middle and the old and weak on the outside. They all want to survive if possible, but their natural mechanism works that the old and weak ones will die first. Survival of the species is more important.

The game of nature
The game plays itself: the one who's the fastest, strongest, cleverest, and the most explosive wins. If you ever saw a documentary on African wildlife, you surely noticed how close predators can come to a herd, without immediately chasing them away... That's because the herd animals feel their focus. In nature, energy is money! It's no use for them to run away and waste valuable energy when they run into another pack of predators who's waiting for them at the next stop. No, they just continue like their noze is bleeding, but in the meanwhile they're thinking their way out. The best way for them to survive is slowly sneak away, without a predator even notices it. After all, they know predators aren't going to throw themselves in the herd and take a lucky shot. Their energy is way to valuable too, they're observing the herd first and pick an easy victim.
So the first stage is the game is: who's the cleverest?

Predators plan their attack, but once they're in attack modus, the adrenaline rushes through their veins to maximise their body strength. This takes a lot of energy. A smart predator will wait until he can do a surprise attack, his changes are bigger when the prey is just scratching his ear. If the prey animal is attentive enough and notices the attacking predator, it has some seconds in its advance. Its energy goes up as well, and runs for it's life. The time between the moment the predator starts to attack and the moment the prey animal runs away is crucial for the game. This stage is defined by who's the most explosive?

After that stage all activity from both teams is going to their feet: they run for their lifes... both of them! A predator only has about 5 attempts to win a game before he starts getting too weak to ever catch a prey again, and is bound to die a slow and painfull death. The one who has the most endurance wins this part. This stage is called who's the fastest?

The finals start when there's an open fight... everything is allowed from both teams and usually the one with the most athleticism wins. Sometimes a prey animal can escape, by kicking and biting... and then pulling back as quick as possible.  Who's the strongest?

Men are predators, we're in the opposit team of nature.

So what's the deal?