Dwarfs descend from the individuals who mutated dwarfism on both sides. No founders of any dwarfism mutations are known. The original founders of the dwarfism
mutations would have been carriers and appear normal because of its recessive inheritance. An example of a recessive disorder in a family tree is HERDA. The Poco Bueno (1944) line is the founding
line of HERDA. No HERDA effected individuals showed up until 1971. This was because inbreeding of the Poco Bueno lines carrying the recessive mutation did not occur until 1971. Dwarfism is
similar in that affected individuals did not show up until later generations.
Since most dwarfs were either not recorded or died at birth, there are no complete records that date back far enough to identify founders of any dwarfism mutations. Gene tests need to be developed to help reduce and attempt to remove the disorder from the gene pool as much as possible. Because dwarfism is recessive, it can hide in a family for numerous generations and even indefinitely if no inbreeding occurs. However, because of the nature of artificial selection, inbreeding will eventually happen even if it happens centuries later.
Dwarfs show up because of inbreeding. This is why some state that dwarfism is caused by inbreeding. Dwarfism is revealed through inbreeding, the mutated alleles cause dwarfism.
In miniature horses of the past, small size was valued over conformation. In the 60's and 70's dwarf horses were winning in the show ring because of their diminutive size caused by their disorder. Dwarf stallions such as Bond Tiny Tim (ACAN) and Del Terras Lord of the Isles (Skeletal Atavism) spread their dwarfism genes to all their offspring (There were other historically prolific dwarf stallions besides these two. Bond and Del Terra's are better known examples.)
Because dwarf stallions were so highly favored for a time, the breed has suffered from the disorder being spread through the effect of Popular Sire Syndrome. A gene flow effect where prolific males greatly spread a trait or disorder within a gene-pool. (The quarter horse stallion Impressive who spread HYPP is another example of a popular sire effect) All descendants of dwarf sires at least carry dwarfism, but not all of their grand-foals do. Although lines that have used dwarves directly should be cautioned, it is good to note that not all animals decedent from these lines will carry the disorder. Regardless, all miniature horse lines are capable of carrying dwarfism regardless of pedigree. It has been estimated that over half of all miniature horses carry some form of dwarfism.
Bond Tiny Tim a 1970 stallion with ACAN dwarfism (Shown as a foal and adult in Identifying Dwarf Foals section) with two of his ACAN dwarf offspring.
Del Terra's Lord of the Isles a 1972 miniature horse stallion with skeletal atavism dwarfism.