Wolf to woof: the evolution of dogs.(Brief Article).Karen E. Lange. National Geographic 201.1 (Jan 2002): p2(10). (1021 words)
Full Text:COPYRIGHT 2002 National Geographic Society
Less than 14,000 years separates them: the wolf--the dog's ancestor--and the Maltese, one of hundreds of breeds of today's Canis familiaris. Humans transformed wild canids into the first domesticated animal--the tamable, trainable, incredibly variable dog.
The Human-Dog Connection
About 12,000 years ago hunter-gatherers in what is now Israel placed a body in a grave with its hand cradling a pup. Whether it was a dog or a wolf can't be known. Either way, the burial is among the earliest fossil evidence of the dog's domestication. Scientists know the process was under way by about 14,000 years ago but do not agree on why. Some argue that humans adopted wolf pups and that natural selection favored those less aggressive and better at begging for food. Others say dogs domesticated themselves by adapting to a new niche--human refuse dumps. Scavenging canids that were less likely to flee from people survived in this niche, and succeeding generations became increasingly tame. According to biologist Raymond Coppinger: "All that was selected for was that one trait--the ability to eat in proximity to people."
At the molecular level not much changed at all: The DNA makeup of wolves and dogs is almost identical.
Breeds Apart One species, hundreds of faces
No other species displays such diversity as the dog. Raymond Coppinger calls the dog a shape-shifter. Yet all dog breeds share certain characteristics, born of their common origin. As early canids adapted to human settlements, they developed tame dispositions and a host of genetically linked qualities, including trainability, tail wagging, and multicolored coats. No longer needing to bring down big prey, dogs developed skulls and teeth that were smaller, relative to their overall size, than a wolf's. Having gone from a diet of meat to eating human garbage, they developed smaller brains, which require less protein and fewer calories for growth and maintenance. The end product was an animal we would recognize as the mutt--similar to the medium-size, often golden-colored dogs that scavenge on the edges of towns worldwide. From this beginning the earliest breeds may have emerged with a minimum of human intervention as people chose and reared dogs for abilities such as guarding or hunting. Environment also shaped early breeds. In cold climates, for instance, larger dogs with dense coats could better survive to reproduce. Over the centuries humans began to crossbreed animals with desirable traits to produce hybrids, creating greater variation in shapes than would appear or survive in nature. These graphs show how the skeleton of the wolf has been manipulated--without losing a single bone. Much of the dog's variation was possible because of genes that affect the timing of its development as a fetus and puppy, which can greatly alter a dog's final shape. Unlike in cats, the heads of puppies are not just smaller but have different proportions than the heads of adult dogs. For example, the skull of a bulldog (below, far left), with its pushed-in upper face and outward jutting jaw, is the result of nose growth that begins late and then proceeds slowly. The rest of its skull forms to fit the short nose. In contrast, the borzoi has a long and slender snout because its nose starts growing early--in the womb. The establishment of kennel clubs in the mid-1800s accelerated the process of artificial selection by encouraging new breeds. Most breeds established since 1900 were created simply for the sake of appearance.
Roots of the Dog
Eight million years ago on what is now the U.S. Great Plains, a powerful canid called Epicyon, the size of a large wolf, attacks a horned herbivore. Nearby a pack of fox size Eucyon surrounds an early peccary. As the climate cooled, Epicyon and others of the subfamily Borophaginae (opposite, below) followed their large prey into extinction. Adaptable Eucyon, with teeth suited for eating both meat and plants, survived. Eucyon species migrated into the Old World (map), eventually evolving into wolves. About 800,000 years ago wolves crossed to Arctic North America.
Paths of Evolution
The dog's lineage began 37 million years ago in North America in predators that had distinctive pairs of shearing teeth and ran down prey. Early canids reached Europe seven million years ago, but it was Eucyon, at far right, moving west six to four million years ago, that gave rise to most modern canids, including wolves, coyotes, and jackals.
The dog evolved in the company of humans and cannot exist without them. Even the vast majority living "wild" as village scavengers depend on proximity to humans. That relationship has become so intimate that dogs are often viewed as creatures apart, writes biologist James Serpell. "The domestic dog exists precariously in the no-man's-land between the human and nonhuman ... neither person nor beast." The ancients saw dogs as messengers between the living and the dead. Today dogs are often used in experiments that might threaten human lives.
Dogs of the Dead
Wrapped to resemble a jackal, the mummy of a young canine was left as an offering in an Egyptian tomb during Roman times. Egyptians did not consider dogs sacred but believed their wild cousin, the jackal (as the god Anubis), guided souls of the dead to the afterlife.
In 1957 a dog named Laika became the first creature to orbit Earth in the Soviet Sputnik 2 satellite. She died in space. Soviets later sent dogs rocketing 50 miles up in pressure suits to prepare for the first manned spaceflight in 1961. Most, perhaps all, survived.
See Spot Rerun
Businessman Lou Hawthorne, coordinator of the Missyplicity dog-cloning project, crouches with Missy, the collie-husky mix whose anonymous owner donated $3.7 million to Texas A&M to copy his pet. Once researchers succeed, Hawthorne is guessing that tens of thousands of dog lovers will be willing to pay $20,000 apiece to clone their animals.
When Sony designed the robot pet Aibo, it chose the form of a dog to appeal to the widest possible market. "We consider it a companion, a mascot," says spokesman Jon Piazza.
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Source Citation:Lange, Karen E. "Wolf to woof: the evolution of dogs." National Geographic 201.1 (Jan 2002): 2(10). General OneFile. Gale. TAMPA HILLSBOROUGH COUNTY PUBLIC LIBRAR. 21 Jan. 2009