Equus Ferus

Today's Wild Horses

 

Actually, those guys fighting are mustangs, aka feral horses, aka horses that were once domesticated but escaped into the wild. ¹ They can be easily re-domesticated/"broken". ⁵ They are the domestic horse, Equus ferus caballus. ¹

Above are pictures of the extinct Eurasian Wild Horse (Equus ferus ferus) that once lived in Eurasia and is considered to be the pre-domestic ancestor of the modern horse, although this is debated.¹

Przewalski's horse (Equus ferus przewalskii)native to Central Asia and the Gobi desert, is the only living wild horse (debatable since it bred a lot with domesticated horses). It went extinct in the wild due to loss of genetic diversity (inbreeding and breeding with domestic stock), hunting, loss of habitat, and loss of water sources. Later it was reintroduced into the wild, and is now a wild horse again.³

The Przewalski has two more chromosomes than our horses, stands 13 hands tall to the shoulder, head and body length of less than 7 ft, and an adult can weigh between 550 and 750 lbs.²

Note the Przewalski's  stylish mohawk mane and can't be tamed attitude.

Domestication

Either the Tarpan or Przewalski's horse could be the ancestor of our domesticated horses.
The earliest evidence for domestication in the archaeological record (dates to 5000 BC) is of post molds at Krasni Yar in Kazakstan which contain a lot of animal dung within its enclosed area; it is interpreted to have been a horse pen, although these horses may have been kept for food and milk rather than riding or load-bearing.⁶

Bit wear on horse teeth, which indicate horseback riding, appear in the archaeological record around 3500-3000 BC in the steppes east of the Ural Mts at Botai and Kozhai. Only few of the horses had bit wear perhaps because most of the horses were kept for food while only few were ridden for hunting. Finally dating at 2000 BC, definitive evidence of  horse domination, drawings of horse-drawn chariots in Mesopotamia (see amazing pictures below).⁶

Finally, the earliest direct evidence of the use of horses as beasts of burden--in the form of drawings of horse-drawn chariots--is from Mesopotamia, about 2000 BC.⁶

Genetic analysis has traced all living domesticated horses to one founder stallion (have the same Y-haplotype); whereas analysis of mitochondrial DNA from female horses reveal 77 possible founding mothers for the current horse populations - which probably means more, actually.
A 2012 study by Warmuth and colleagues, integrated data about horse domestication to conclude that the domestication occurred once in the western Eurasian steppe. The diverse mtDNA was probably due to repeated breeding events with wild mares.⁶

In a 2009 study of Botai sites dating 3500-3000 BC by Outram and colleagues, evidence was found for gracile horse shin bones, horse milk consumption, and bitwear on teeth. Gracile metacarpas indicate domesticity because domesitic horses have thinner shins. The Botai horses had shinbones closer in size and shape to fully domesticated horses of the Bronze Age. Also, fatty lipids of horse milk were found inside of pots; and, as mentioned earlier, the horse teeth showed signs of bit wear (image below shows parallel-sided vertical band of bit wear).⁴

 

Works Cited
1. http://en.wikipedia.org/wiki/Wild_horse
2. http://en.wikipedia.org/wiki/Tarpan
3. http://nationalzoo.si.edu/animals/asiatrail/fact-phorse.cfm
4.  http://www.aaas.org/news/releases/2009/0306sp_horse.shtml
5. http://www.training-horses-naturally.com/wild-horses.html
6. http://archaeology.about.com/od/domestications/qt/horses.htm


 Pictures
Mustang picture: http://ngm.nationalgeographic.com/2009/02/wild-horses/fuller-text
Tarpan pictures  http://en.wikipedia.org/wiki/Tarpan
Running Przewalski's horses: http://nationalzoo.si.edu/animals/asiatrail/fact-phorse.cfm
Can't be tamed picture and person with horse: http://animals.nationalgeographic.com/animals/mammals/przewalskis-horse/
Botai tooth http://www.aaas.org/news/releases/2009/0306sp_horse.shtml\
Horse drawn chariot left picture: https://ucworldstudies.wikispaces.com/Weapons
Horse drawn chariot right picture: http://www.britishmuseum.org/about_us/news_and_press/press_releases/2012/the_horse.aspx