* Evolutionary History: All horse breeds, even those considered "pure" today, have a shared ancestry. Over thousands of years, selective breeding has created distinct breeds, but their genetic makeup still reflects their common origins.
* Historical Interbreeding: Throughout history, breeds have been intentionally or unintentionally crossed. This crossbreeding has introduced genes from other breeds into the gene pool.
* Natural Selection: Even within a breed, natural selection favors certain traits, which can lead to genetic changes over time.
What you *can* have are breeds that are considered "pure" based on breed standards and registries:
* Purebred: This refers to horses registered with a breed association, meaning they meet specific criteria for their breed, often involving lineage tracking back to founding animals.
* "Pure" in a More Relaxed Sense: Some people use "pure" to mean a horse that looks very typical of its breed. This isn't a scientific term, but it reflects the idea that the horse's appearance is largely free of obvious traits from other breeds.
Therefore, there is no horse breed that can truly be considered "pure" with absolutely no influences from other breeds. It's more accurate to talk about the relative purity of a breed based on its history, breeding standards, and genetic makeup.