It seems that one of the most common questions we are asked about Caspians is: "Are they horses or are they ponies and what makes the difference?" The answer to this question has been developed through DNA studies done by Dr Gus Cothan. I will not go into the details of this here. The details are available in various other sources. Here we will attempt to give you the the short and simple answer.
First, the difference between horse and ponies has nothing to do with size. There are Welsh Cob ponies that are larger than some horses. The difference has more to do with the nature of the animal and this difference in nature comes from their differerent genetic backgrounds. In primeval times, before recorded history and before man influenced the movement and breeding of horses the were 4 horse type animals. They were seperated geographically and came from different climates across Europe and Asia.
Pony I was the ancestor of the Shetland Pony and similar breeds. Pony I developed in Northwestern Europe in a rather cold wet climate. He was about 12 hands high, stocky, thick skinned, and pretty hairy. Pony I is the source of the "cold blooded" and somewhat stubborn nature we see in ponies to this day.
Pony II was the ancestor of Przswalski's Horse. Pony II developed in another cold climate, North Eurasia. He was also stocky and hairy but somewhat heavier than Pony I. Pony II was dun or cream color and was the source of the "dun factor" we sometimes breed for today.
Horse III was larger and much less hairy. Horse III developed in central Asia and eastern Europe. This horse turned into the Andalusian that we have today.
Horse IV developed in southwestern Asia. Horse IV was adapted to hot and arid climates. Horse IV was thin skinned, slick coated, and "hot blooded." He was again only 12 hands high but he was not a pony, he was the ancestor of the Arabian. DNA studies reveal that the Caspian Horse is about the closest thing (and the Caspian is quite close) to Horse IV that exists today.
Sometimes one hears the Caspian Horse refered to as a "miniature Arabian." This is purely descriptive as the Caspian is not a miniature horse. Miniature horses are the result of selective breeding. They are manmade and date back about 400 years. The Caspian Horse is the result of natural selection in wild herds and dates back thousands of years.
Having said all that many people still call them Caspian Ponies because some people define anything under 14 hands as pony. Then there is Pony Club which is a great international organization for young people. Pony clubbers refer to all their mounts as "ponies."