Those New Tricks Came From Old Dogs
In the genetic journey from wolf to lapdog, dogs developed a unique genius for sensing human intentions, as the interplay of handler and hound shaped the biology of canine behavior in ways that scientists only now are beginning to understand, new research shows.
Dogs are tailored to fit the human mind, like a glove to the hand.
From birth, dogs are fluent in the human text of hand gestures and facial expressions. Their ability to understand humans is better than chimpanzees -- humanity’s closest relative -- or the gray wolves from which dogs are descended, according to the first direct comparison of the species. Harvard University anthropologist Brian Hare, who conducted the comparison, publishes his experiments today in the journal Science.
This unusual canine social skill does not come from training or experience; nor is it the legacy of a pack species with its own rich vocabulary of body language, Hare said. It arises from genes shaped by human contact, inherited by every contemporary dog, his experiments suggest.
“We have created the dog in our own image,” said developmental geneticist Jasper Rine at UC Berkeley.
Through a series of research papers in Science, three independent teams of scientists, including Hare, explored the evolution of dogs -- from feral scavengers to man’s best friend -- to better understand one of humanity’s earliest innovations: the domestication of animals.
By analyzing canine DNA from around the world, the researchers determined that the domestication of dogs was an inspiration that swept the ancient world more quickly and more recently than previously believed. Every one of nearly 400 breeds today descends originally from just five female wolves in East Asia, scientists said.
As perhaps the first wild animal to fall under human sway, dogs offer an unusually clear window into how genes and selective breeding can shape behavior. People have manipulated virtually every aspect of canine design and demeanor, culling for those traits that humans deem most useful in these cold-nosed companions.
Dogs trace their ancestry to primordial wolves that thrived about a million years ago, said Xaoming Wang, an expert on vertebrate paleontology at the Natural History Museum of Los Angeles County. In all, there are 35 canine species alive today, only one of which -- the domestic dog -- is the object of human affection.
The earliest fossil evidence of this special relationship was unearthed from a grave in Israel, dating from about 12,000 years ago. In its left hand, the human skeleton cradled a pup.
By themselves, however, these poignant remains do not reveal whether the bones belong to a dog or a wolf, or why they were cherished. So far, no fossil shows where, when or why these animals were first domesticated.
“There are very few hard facts about the origin of dogs, just a lot of guessing,” said geneticist Peter Savolainen of Sweden.
In search of reliable answers, the scientists turned to the animals’ DNA, gathering genetic material from hundreds of dogs in Europe, Asia, Africa, the Americas and the Arctic. Researchers also successfully exhumed DNA from fossil remains of dogs that lived in North and South America before Christopher Columbus and European settlers began arriving.
These DNA samples all were extracted from the tiny energy-producing parts of the cell called mitochondria, which are inherited relatively unchanged from the mother. That allowed researchers to trace a direct genetic line of descent across thousands of years.
Their findings suggest domestication was a canine epic that began more recently than previously believed and originated in East Asia, far from the Middle East, the region long considered the cradle of agriculture and animal husbandry.
Analyzing a global canine menagerie, Savolainen at the Royal Institute of Technology in Stockholm and colleagues at the Chinese Academy of Sciences determined that dogs may have been domesticated perhaps just 15,000 years ago, compared with previous estimates of 100,000 years ago or more.
In the largest study of its kind, they looked at the genetic variations in 654 domestic dogs and 38 Eurasian wolves.
The scientists used minute genetic differences between the animals to calibrate a kind of molecular clock that allowed them to estimate the pace of canine evolution and to gauge its epicenter.
“We see that there is much higher genetic variation in East Asia than in other parts of the world. That suggests to us that dogs originated there, and a few dogs then spread to other parts of the world, taking just part of that genetic variation with them,” Savolainen said.
At a time when stone tools, spears and fire were high technology, the radical idea of a working partnership between man and beast spread quickly among nomadic tribes.
Dogs reached the Americas with the first human settlers of the Western Hemisphere about 12,000 years ago, researchers at the National Museum of Natural History and UCLA concluded in a separate study.
“Our results suggest the dogs walked with them across the Bering land bridge” from Siberia to Alaska, said UCLA evolutionary biologist Robert Wayne. “They were already a fundamental part of human society.”
Not everyone is happy with the idea that dogs might have been domesticated so recently.
Some, like Wayne, are convinced that the process was far more gradual, beginning as much as 100,000 years ago. That would allow more time for the species to be tamed and then gradually integrated into human life.
Others suggest that the very speed with which the partnership became part of prehistoric human culture is a measure of just how indispensable dogs had become to humans as all-purpose, living utility tools, experts said.
“There must have been something advantageous about those dogs that made them extremely successful and allowed them to spread all over the world,” said Carles Vila of Uppsala University in Sweden. “If dogs were, for example, improving the quality of hunting, that would be a very great advantage for humans. It could even have made the colonization of the New World easier.”
Wayne and other researchers led by Smithsonian geneticist Jennifer Leonard initially looked at mitochondrial DNA isolated from ancient dog remains from Latin America and Alaska to see whether dogs had evolved independently in the New World.
Dogs were common in the Americas long before Europeans arrived. The oldest known dog remains in the Americas, discovered in Danger Cave, Utah, date from 10,000 years ago, comparable in antiquity to canine remains unearthed at sites in Germany, Israel and Iraq.
That left researchers wondering whether dogs had indeed spread so quickly around the globe in the eons before transoceanic travel, or whether native American dogs, such as the Eskimo dog, Mexican hairless and Chesapeake Bay retrievers, were descended from American wolves.
Leonard’s team reconstructed their pedigree by examining DNA from 37 dog remains from pre-Columbian Mexico, Peru and Bolivia and discovered some unique genetic types.
The researchers also looked at genetic sequences from dog remains unearthed in Alaska that date to a time before European explorers arrived in the region.
The dogs of the Western Hemisphere -- ancient and modern -- owe their origins to the same East Asian wolves that gave rise to all other dogs, Leonard determined.
Those Western Hemisphere breeds that do survive today, such as the Eskimo dog and the Mexican hairless, genetically are virtually indistinguishable from Eurasian dogs. The unique strains identified in the ancient remains are nowhere to be found today. Leonard speculated that those native American dogs had been systematically eliminated by European colonists.
“Some of these native American heritages have not been preserved in the present gene pool of dogs,” Leonard said. “Several things might have happened. The conquistadors may have purposefully killed off the dogs. The new European dogs also may have had more status appeal.”
A still unresolved scientific question, the researchers said, is just which species -- humans or wolves -- made the first move in the collaboration.
Wolves may have initiated the relationship, attracted by the refuse accumulating around prehistoric human campsites.
Nor is it entirely clear, Rine said, just which species is truly the senior partner or how the company of dogs has altered the biology of human character.
“My dog can get me to give her affection any time, any place she wants,” Rine said. “I would say I am extraordinarily well-trained.”