No observer can help but remark upon the incredible variety of sizes, shapes, temperaments and behaviors of the dog—from the one-pound Chihuahua to the 200-pound Mastiff; the stubby-legged, placid Basset Hound to the long-legged, fleet Greyhound. Nowhere else in the animal kingdom does so much morphological diversity exist within a single species.
In large measure, the 400 or so breeds of dog extant today are products of human breeders, who, as Charles Darwin pointed out nearly 150 years ago, have selected consciously and unconsciously for specific physical and behavioral traits. But dogs are also the products of 40 million years of canid evolution through natural selection. The forces of evolution created the unique physiological and behavioral characteristics— the senses, physical abilities, social and individual behaviors and brains—that made the wolf the ideal progenitor of the dog. Those attributes resonate in human myths from around the world that ascribe to canids wild and domestic central roles in the creation of humans, guarding the dead or guiding them to the afterlife and serving as intermediaries between humans and nature.
Various legends of the dog as a fell beast and spreader of violence and disease are also widespread, reflecting a less exalted place in human affairs. But it is the diversity and malleability of canid characteristics that have made dogs indispensable allies of humans for more than 100,000 years—longer than any other domestic animal.
From an evolutionary perspective, the diversity found in the domestic dog echoes trends in wild canid evolution, albeit on a much different time scale. Rising from a common ancestor, new species of wild canids spread over millions of years into nearly every type of habitat on Earth. Today, 35 species of canids are found on every continent but Antarctica. However, centuries of persecution to protect domestic livestock and harvest furs and trophies, along with habitat destruction, have brought several of those species, including the African wild dog and the little Ethiopian wolf, close to extinction. Other species, like the gray wolf, have been extirpated from much of their historic range. Yet the dog, the coyote and some foxes continue to flourish. The signal difference is that dogs have evolved almost exclusively through artificial selection by humans while wild canids have evolved through natural selection.
The full details of canid evolution, including development of the dog, remain unclear because of the incomplete nature of the fossil record, but what we do know reveals how a remarkable group of predators evolved and what they have meant to the natural and built worlds. In an effort to capture this rich story, the Natural History Museum of Los Angeles County has created an interactive multimedia exhibition exploring canid evolution and the role of dogs in human societies. As scientific advisors of “DOGS: Wolf, Myth, Hero & Friend,” we will be working on a book to accompany the exhibition.
The exhibition and national tour is made possible by Pedigree® Food for Dogs and is supported by a generous grant from the National Science Foundation. The exhibition premieres at the Natural History Museum of Los Angeles County on October 13, 2002, and over the next five years is scheduled to travel to San Diego and San Bernardino, California; Seattle; Mesa, Arizona; Omaha; Washington, D.C; Milwaukee; Philadelphia; Cleveland; and Chicago, with more cities to be announced.
The evolutionary history of dogs begins some 40 million years ago in North America, when Hesperocyonines, looking like a cross between a fox and a weasel, emerged from the soup of carnivores. Hyena-like canids, the Borophagines, or “bone-eaters,” with bone-crushing jaws, followed and persisted until around 2.5 million years ago, when the last one vanished.