Why do Rhodesian ridgebacks have ridges? It's this breed's most known feature, a line of hair running on their backs in the opposite direction from the rest of the coat. People who aren't much acquainted with this breed may wonder if those hairs are growing that way because of a previous surgery, or in some cases, may exchange them for a dog's hackles, those hairs that rise when dogs feel an assortment of emotions such as fear, arousal, surprise, insecurity, excitement, nervousness or defensive behaviors. Instead, in the Rhodesian ridgeback those hairs are simply a unique trait that the breed sports for many centuries.
A Matter of Standard
The ridge on the Rhodesian's back is such an important feature in this breed that a ridge-less specimen is means for disqualification in the show ring. According to the American Kennel Club standard, the ridge is this breed's hallmark and regarded as the characteristic feature of the breed.
The breed standard calls for a ridge that is clearly defined, symmetrical and made of hairs growing in the opposite direction compared to the rest of the coat. The ridge starts right behind the shoulders and tapers off to a point as it reaches the hip area.
The ridge should also have two crowns (whorls) that are directly opposite to each other. Having only one whorl or having more than two is considered a serious fault.
A Look Back
In order to understand why Rhodesian ridgebacks have the characteristic ridge, one must take a glimpse into this breed's past. Historic data shows that this breed was developed in Zimbabwe, Southern Africa. Back in the 17th century, the rocky Cape peninsula in the south-western extremity of the African continent, was inhabited by the Khoikhoi population which began trading with the Dutch during this time. An indigenous half-wild African dog was often seen back in those days and its most prominent feature was the hair growing in the reverse direction along the back.
The Dutch who converted wild lands into farm lands during their many years of trading there, decided to put these African dog to good use allowing them to hunt and defend their herds of cattle and homesteads from lions.
These dogs then later on interbred with the several dogs imported from Europe which included great Danes, bloodhounds, greyhounds, and terriers.
Later on, breeds imported from Arabian traders and Asian immigrants further contributed to Rhodesian ridgeback's genetics. Breeders selectively bred for the ridge as they noticed how specimens with the ridge had a tendency of making excellent hunters.
A Dominant Trait
Rhodesians who have the ridge either carry two copies of the ridge gene (homozygous) or carry just one copy of the ridge gene (heterozygous). The Rhodesians with the ridge who carry 2 copies of the ridge gene will never produce puppies without the ridge. When crossed, all they have to do to pass down the ridge trait is to give one copy of their two ridge genes, which is dominant. Therefore, all puppies born from a homozygous Ridgeback parent will have a ridge, regardless of what the other parent has, but their genetic tendencies will vary, resulting in:
- puppies who have ridges and a 50 percent chance of carrying 2 ridge genes (homozygous), or
- puppies who have ridges and a 50 percent chance of carrying 1 ridge gene (heterozygous)
When Things Go Wrong
As we have seen, the ridge is a dominant trait, but if it's a dominant trait, why do Rhodesian specimens without a ridge pop up every now and then? Problems arise when two Rhodesians with only one ridge gene (heterozygous) are crossed. The lack of ridge is therefore the result of crossing two heterozygous Rhodesians. The breeding of such specimens can result in the following scenarios:
- Puppies who have ridges and carry 2 copies of the ridge genes (which makes them capable of passing down the trait regardless of who they're bred to)
- Puppies with a 50 percent chance of having a ridge, but having only one copy of the ridge gene.
- Puppies with a 25 percent chance of not having the ridge. Puppies not having the ridge, lack the ridge gene and therefore cannot produce any offspring with ridges. The ridge should be fully visible in puppies from the day they are born, so don't believe breeders who say it will grow later, warns the Rhodesian Ridgeback Club of the United States, Inc.
A Weak Spot
The Rhodesian's ridge is the breed's most prominent feature, but this strong point is also the breed's weakest link when it comes to congenital defects. Breeders and researchers have found a correlation between the presence of the ridge with a congenital defect known as "dermoid sinus." The same autosomal dominant mutation that's responsible for the ridge is what also predisposes for this condition, according to a Doctoral Thesis. Not coincidentally, this defect is found in two breeds in the world with a ridge: the Rhodesian ridgeback and the Thai ridgeback.
Fortunately, this genetic skin condition is rare. A dermoid sinus develops during the embryonic stage. In normal development, the neural tube separates from the skin, but in dogs with dermoid sinus, it fails to, therefore there's an incomplete separation of the skin from the nervous system, according to the American College of Veterinary Surgeons. Being hereditary, puppies with condition should have the abnormal tissue removed and they should be altered so to prevent them from passing down this defect.
Legend Has It
A cute explanation for why Ridgeback's have their characteristic ridge comes from The Rhodesian Ridgeback Club of the United States’ Health & Genetics Committee. For those who think the ridge looks like a surgical incision gone bad, owners can give this explanation:" Oh, you're talking about that ridge? That's "where God sews them up when he’s done stuffing them."
Did you know? The only way to tell whether a Rhodesian has one or two ridge genes is through genetic marker testing, which is now provided by the GenoCan project.