“The dog is everywhere what society makes him,” wrote Charles Dudley Warner in the January 1896 issue of Harper’s New Monthly Magazine. Elaine Ostrander and Heidi Parker update that message in the November 2005 issue of the online journal, Public Library of Science—Genetics: “The domestication of the dog from its wolf ancestors is perhaps the most complex genetic experiment in history, and certainly the most extensive.” Undeniably, the results of that experiment are directly manifest in the appearance and behavior of the dog.
Since hitching its evolutionary fate to that of humans some 9,000 canine generations ago, the dog has proven the most adaptable, versatile and steadfast of companions, serving as a guard; draft animal; hunter; herder; warrior; entertainer; finder of explosives, contraband, disease and lost souls; healer, therapist; physical and spiritual guide; and friend. With the public unveiling last month of the fully sequenced and richly annotated dog genome—the approximately 2.4 billion base pairs of DNA (A [adenine], which always binds with T [thymine], and C [cytosine], which binds with G [guanine]) that form its genetic code—the dog might now also add to its monikers, shall we say, “genomic consort.”
Of course, the dog is not the first mammal other than humans to have its genome fully sequenced—the mouse, rat and chimp got theirs first—but because of its architectonic breed structure, it might prove the most illuminating. To shift metaphors: geneticists can now use the dog genome sequence like a combination zoom and telephoto lens, zeroing in on specific genes and even minute changes within genes, or jetting back to examine broad patterns and interrelationships within it and between it and other genomes that reveal the evolutionary history of an individual, a breed, a population, or the entire species and genus.
Dog as Cultural Construct
A cultural and biological construct from the start, the dog is a mash of intensive human tinkering and the natural proclivities both of its wolfish fore bearer and of its randomly breeding dog ancestors. Indeed, the newly released analysis of the sequenced dog genome points to two unmistakable genetic bottlenecks—about 9,000 generations (taken by the sequencers as 27,000 years) ago, when perhaps as few as two tamed wolves produced the first litters of what became dogs. Since then, through what Darwin called conscious and unconscious selection, humans have cleaved the dog into breeds, in effect making it the most variable of mammals in terms of size and shape, with the exception of humans themselves. The most intensive period of breed formation occurred between 100 and 300 years ago, coincident with the rise of “scientific breeding” and clubs devoted to the cult of purebred dogs, primarily in Europe and North America.
By most estimates, there are today more than 400 breeds worldwide, many with specialized morphologies and behaviors, nearly all genetically isolated. The majority of those breeds are also susceptible to one or more of more than 400 genetic disorders, approximately 350 of which are also found in humans, including epilepsy, kidney cancer, deafness, blindness, auto-immune disorders, congenital heart disease, skeletal malformations, neurological abnormalities, bleeding disorders and neuropsychiatric disorders.