This Halloween, many dogs are wearing a piebald costume. Let's get this out of the way. Piebald has nothing to do with pieing bald people in the face.
In fact, piebald describes a physical characteristic found in many domesticated animals. Instead of walking around with the coat of their wild ancestors -- one that is well adapted for the natural environment and can provide camouflage -- domestic animals show up to the party essentially wearing a colorful suit.
A piebald coat is one "completely lacking pigmentation in specific body areas," explains Lyudmila Trut, head of the Institute of Cytology and Genetics of the Siberian Department of the Russian Academy of Sciences. A piebald pattern is typically white spots or splotches on a colored background, or vice versa.
Trut's research group began in the late 1950s by Dmitry Belyaev to investigate the complex changes that occur during domestication using the silver fox, Vulpes vulpes, as a model species. Breeding human-friendly foxes, they found, produced offspring that not only were even more human-friendly, but the foxes also developed particular physical (or morphological) changes like wavy or curly hair, rolled or shortened tails, floppy ears, as well as a piebald coat, i.e., a coat with spotting of two different colors, often black and white. Look around and you'll see that domesticated animals are teaming with this coat pattern. Once piebald is part of your vocabulary, you're sure to spot it everywhere! Get it? Ha.
Even donkeys come with white spots, as Albert Ernest Jenks pointed out in a 1916 paper with the super catchy title, "Spotted Asses: An Animal That, Like the Camel and Elephant, Rarely Has Spots--Piebalds More Common in Other Domesticated Animals--Selective Breeding Probably Largely Responsible for This Albinism."
If you got through that longwinded title, you might have caught Jenks' suggestion that selective breeding could be behind the piebald coloration. Trut's research would seem to agree. Foxes were not being bred for a particular physical appearance, but by breeding for friendliness toward humans, other physical changes came along for the ride. One common piebald pattern is the Star mutation, seen below, which appears among different domesticated animals. This pattern often shows up as a loss of pigmentation on the head as well as on the body.
If you're wondering whether to plop a costume on your companion dog this Halloween, just keep in mind that he might already be dressed up in his "domestic dog" outfit.