Short answers, pulled from the story.
The horse first appeared on Earth between 45 and 55 million years ago as a small, multi-toed creature known as Eohippus. This animal roamed the forests of North America before evolving into the large, single-toed Equus ferus caballus that humans know today.
Humans began domesticating horses around 4000 BCE in Central Asia. The earliest archaeological evidence of attempted domestication was found in the lower Volga-Don region of the Western Eurasian Steppes.
The horse skeleton averages 205 bones and differs significantly from the human skeleton. The forelimbs are attached to the spinal column by a powerful set of muscles, tendons, and ligaments because the horse lacks a collarbone.
A horse's life expectancy ranges from 25 to 30 years, though uncommonly a few animals live into their 40s and occasionally beyond. The oldest verifiable record is Old Billy, a 19th-century horse that lived to the age of 62.
There are more than 300 breeds of horse in the world today, loosely divided into three categories based on general temperament. These categories include spirited hot bloods, cold bloods such as draft horses, and warmbloods developed from crosses between the other two types.
The first archaeological evidence of horses used in warfare dates to between 4000 and 3000 BCE. The use of horses in warfare was widespread by the end of the Bronze Age.