Why do dogs have dewclaws
Dogs have dewclaws for stability and grip; front ones are functional digits while rear ones vary by breed, often vestigial but sometimes essential for work.
Dogs have dewclaws because they are functional digits that provide stability and grip during movement, though their utility varies significantly between front and rear legs. While front dewclaws are well-developed and touch the ground to prevent leg twisting, rear dewclaws are often vestigial with little bone structure, yet remain critical for specific working breeds.
Front dewclaws are functional, not vestigial
The dewclaw on a dog's front leg is a digit that grows higher on the leg than the rest of the foot, similar to a human thumb. Unlike the rear dewclaws found in many breeds, the front dewclaw has substantial bone and muscle structure. It is connected to the lower leg by several tendons that link to muscles, allowing it to move independently.
When a dog runs, stop-action photography suggests the entire front foot, including the dewclaw, makes contact with the ground. The dewclaw digs in to prevent twisting or torque on the rest of the leg. This mechanical function is so important that dogs without front dewclaws appear to have higher rates of foot injuries and are more prone to developing arthritis. For working dogs, amputation is generally discouraged unless the digit suffers a traumatic injury that requires removal.
Rear dewclaws are often vestigial but breed-dependent
While most canids have four claws on their rear feet, some domestic dogs possess an additional claw, or rarely two, on the inside of the hind legs. These are technically known as hind-limb-specific preaxial polydactyly. In many breeds, these rear dewclaws have little bone or muscle structure and are attached to the leg by skin only, making them functionally vestigial.
However, for certain breeds, these digits are a necessity. The Beauceron, for example, requires rear dewclaws for sheep herding and for navigating snowy terrain. The presence and structure of rear dewclaws are controlled by genetic mechanisms involving the LMBR1 gene and related parts of the genome. In breeds where they are not required for work, they are often removed to prevent snagging, but in working lines, they are retained for their utility.
The evolutionary history of the digit
The term "dewclaw" has been in use since the 1570s, with the "dew-" element possibly referring to the claw's tendency to brush dew away from grass, though the etymology is not entirely clear. Evolutionarily, the dewclaw is a vestigial digit found on the feet of many mammals, birds, and reptiles. In digitigrade or unguligrade species, it grows higher on the leg so it does not touch the ground when standing still.
While many animals have dewclaws, other similar species do not, such as horses, giraffes, and the African wild dog. In the cat family, including lions, the front dewclaw is not vestigial; wild felids use it as an additional claw to catch and hold prey. In hoofed animals like cattle, dewclaws are often smaller than the main hooves and may never touch the ground, though in pigs and deer, they can reach the ground in soft conditions or during jumping, sometimes used for grooming or mating.
Why removal is a matter of function, not just aesthetics
Because front dewclaws are integral to the mechanics of the leg, removing them can compromise a dog's stability and increase the risk of injury. The tendons that connect the front dewclaw to the muscles in the lower leg are a key part of the leg's support system. Veterinarians recommend that for working dogs, dewclaws should not be amputated routinely.
If a dewclaw does suffer a traumatic injury, the problem can be dealt with at that time, including amputation if needed. This approach ensures that the dog retains the structural support the digit provides while addressing immediate health issues. The decision to remove a dewclaw should always weigh the specific breed's working requirements against the risk of injury.
In summary, the dewclaw is not a useless appendage but a specialized digit that has evolved to serve different functions depending on its location on the leg. Front dewclaws are essential for stability and injury prevention, while rear dewclaws are a breed-specific trait that can be vital for working dogs or vestigial in others.