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. The original breed standard was drafted by F. R. Barnes, in Bulawayo, Southern Rhodesia. The eyes should be round and should reflect the dog's colour: dark eyes with a black nose, amber eyes with a brown (liver) nose. Ridgebacks have a strong, smooth tail, which is usually carried in a gentle curve backwards. 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.