Its forebears can be traced to the semi-domesticated, ridged hunting dogs of the Khoikhoi, which were crossed with European dogs by the early colonists of the Cape Colony of southern Africa. It is not known if these two first direct ancestors of Rhodesian Ridgebacks had dorsal hair pattern ridges themselves, but they founded the Rhodesian Ridgeback bloodline, so either carried the trait or it was added from other Boer dogs and hybrids with Khoikhoi ridgebacks which van Rooyen bred into his lines over many trials then generations. Heterozygotes are detected by mating the animal in question to either known heterozygotes or known homozygous recessives (other methods exist such as mating to offspring, but result in inbred offspring) and a heterozygote is detected when a ridgeless pup is born. Note that many matings are required to have a high probability of detecting a homozygous dominant (once a ridgeless pup is produced, the animal in question is assumed to be heterozygous without question), and more than one sire can produce the pups in one litter.