The Evolution of Canis familiaris
Canis familiaris, is more commonly known as the dog: man’s best friend. Today there are more than 400 million dogs living among us, and more than four hundred and twenty different breeds of dogs all ranging in size from a Chihuahua (6 inches at the shoulders) to the Irish Wolfhound (32 inches at the shoulders) (1). Even though there is a great variability of dogs, they are all considered the same species. So the question remains: why is there such variability and how was it possible to achieve this? The answer is simple: humans. Over thousands of years, humans have driven the evolution of the dog, by selecting for traits and abilities which we found desirable: guarding, hunting, color, size and affection toward us (humans) (2).
Dogs are carnivores, the direct decedents of wolves. Yet the evolution of dogs starts 40 million years ago on the great plains of North America, with the emergence of Hesperocyoninae. These were the first small ground dwelling creatures, evolving from tree dwelling carnivores (Miacis) that fed mainly on birds and insects. The Hesperocyon
were small, about the size of a fox, yet had long legs for running though the plains and big sharp teeth to catch prey; this first group of canines became the dominant carnivores of their time (1,2,3). Then later, about 30 million years ago Borophaginae immerged and
quickly became a dominate species. The Borophagus, was a much larger creature than its
predecessor, about the size of a bear. This animal is the ultimate of bone crushing dogs, equipped with a powerful lower jaw and large sharp teeth. This animal was very strong and powerful enough to bring down the largest of prey. The Borophagus was one of the
first creatures that had organized hunting practices, to bring down the large pre-ice age creatures of the time. Yet, the Borophagus went extinct with their prey at the beginning
of the ice age, allowing their niche to be filled by ancestors of the modern Caninae
family(1,2,3,8). The first member of the Caninae family is named Eucyon, which was a
very adaptable animal compared to it predecessors and was able to survive the ice age much more effectively. First of all it was smaller, and therefore didn’t rely on hunting
such large prey. Also its teeth and stomach had adapted to chew and eat both plants and meat, allowing for a more variable diet than just eating meat alone. The Eucyon
eventually spread all over North America, Asia and Europe; where it then evolved into many common canines today: the wolf, the coyote, and the jackal (1,2,3,8).
7 million years ago the descendents of these extinct Eucyon eventually crossed the
land bridges present between North America and Asia, to spread all over Asia, Europe and Africa. Then about 1 million years ago, grey wolves, or Canis lupus, evolved in
what is believed to be Southeast Asia (based on fossil evidence) and became the most dominate species of the canine group. These grey wolves in turn migrated all over the northern hemisphere hunting large game; such as deer, elk, and moose, in packs. These wolves then, through domestication by the human hand, evolved into what we know now as the common dog, Canis familiaris (2,3,8).
The exact date as to when the domestication of dogs occurred is a subject of much debate, and is something that evolutionary molecular biologists still do not have the answer. Fossil records start detecting a difference between wolf and dog fossils about
14,000 years ago (1,2). Therefore until recently the dog was thought to have evolved quite quickly from its wolf parents. Yet this theory is only congruent with the domestication of dogs occurring only once, making all dogs the decent of one wolf mother and father. More likely the scenario is that there were several groups of wolves domesticated at different times and then the interbred with one another to give us what we now know is the dog, but we still do not know when this occurred. Then in 1997 study based on the mitochondrial DNA of wolves and dogs, performed by Robert Wayne and his team of researchers, said that this date could be pushed back further to more than 100,000 years ago (4).
Wayne used the mitochondrial DNA sequences from 162 wolves from twenty seven locations worldwide and compared those wolf sequences to 140 domestic dogs of sixty seven breeds (4). What Wayne found was that, dogs were the direct descendents of wolves, but that the sequence divergence present between the two family’s suggests that dogs had originated from wolves as much as 135,000 years ago (it is possible that this estimate could be inflated) and that dogs are most closely related to wolves found in East Asia. Yet, wolf and hominid bones have been found in close proximity as long ago as 400,000 years (4). Although sequence estimates place humans domesticating wolves a very long time ago, morphologically and phenotypically the divergence of dogs was not evident until about 15,000 years ago when hunter-gatherer societies switched to agricultural societies. Although throughout this time dogs and wolves did exchange genes, and still do, this wild gene reservoir possibly allows for the great diversity of phenotypes present today (5). All this while, the genomic DNA sequence variability
between wolves and dogs is only 0.2%, making them genetically almost identical species (6).
So now the question is: how and why were wolves domesticated? Well, there have been many theories as to how this domestication did take place. There is no doubt that dogs are the oldest of all domesticated species and their domestication was based on a mutually beneficial relationship with man, a symbiotic relationship. It is theorized that wolves were eating human garbage and scraps, living on the outskirts of society thriving on human refuse dumps, a niche which humans created (2). Eventually these wolves were captured and used as food for our ancestors, but while we had them tied up we realized that when they barked it was an early warning for us that their was either another animal around, or that anther human was present we were unaware of. Therefore humans first used wolves as a guard or initial alarm to danger, and as protection from other animals. Eventually dogs were then used to help us hunt, through tracking down prey. In turn for their protection, eventual companionship, and help with tracking and hunting we provided them with food and shelter, which made a very easy life for most of these dogs and in turn made tracking easier and the nights less frightful (2,5,7).
Many of the variable traits seen today in dogs can represent adaptations according to their environment. Body size and proportion as may represent adaptations to a specific environment or to a specific type of food source. Yet this does not explain the vast phenotypic difference seen between different breeds of dogs, for instance when comparing pugs to greyhounds or for that matter between dogs and wolves. Also it is
hard to see how all these traits could be derived from a single ancestor. This variability is not seen in the wild wolf population (5,7).
Humans for thousands of years bred dogs for specific jobs, characteristics and associated behavioral traits. We have been able to mold dogs into the creatures we see before us everyday, through selecting traits which we enjoy or find helpful and then forcing dogs to reproduce with one another: an unnatural selection or artificial “evolution”. Originally we most likely selected for animals that were less aggressive and better at begging for food (2,3). Over time, domesticated wolves lost a lot of their wolf-like characteristics. These domesticated wolves no longer hunted game, but instead lived off the remnants of human waste, garbage and other scrap food we did not eat. Therefore these domesticated wolves’ heads, teeth and bodies, grew smaller and more slender.
They no longer needed large heads, to support their powerful jaws and large teeth used for bringing down large prey, for they developed another food source: a symbiotic relationship with humans, in which these domesticated wolves were given food for their services, protection and companionship they offered us (5,7).
Years of selective breeding by humans has resulted in the artificial "evolution" of dogs into many different types. This is why we see such a variation in types of dogs today. The first dogs humans probably bred for was probably similar to a greyhound or bird dog: A slender and sleek dog, which could run fast, long distances to track game, and while at night it was able to alert us to danger (1,2 9).
Most recently in 2001, in what is now Israel, a 12,000 year old skeleton was found buried in a grave with its hands clutching a puppy. Whether the puppy is a dog or a wolf is unknown, but regardless this is among the first and best evidence of the dog’s
domestication (2). The first undisputed evidence of the modern dog appeared in China about 5,000 years ago, when the Chinese first started farming rice, this information is gathered from both fossil and picture (drawing) information. Later, the first breed of dogs to have emerged were first described and recognized in Babylon and Egypt about 4,500 years ago (7).
There are now 400 million dogs alive in the world today, while they outnumber their parent wolf population by 100 times, there are only 400,000 wolves worldwide (1). With the molecular makeup of wolves and dogs almost identical it is amazing to see the diversity of dogs present today. Dogs have a vast size range from the tiny Chihuahua, to the massive St. Bernhard. There are also many different body types present as well; there is the short, stout bull dog to the large fluffy cuddly sheep dog. There are over 420 known breeds all with a specific look, nature and temperament about them (1). Dogs are amazingly diverse and incredible creatures, they certainly earn their title as “man’s best friend.”
1. Lemonick, Michael and van Dyk, Deirdre. The Mother of All Dogs. Time. December 2,
2002. Vol. 160 Issue 23.
2. Lang, Karen. From Wolf to Woof. National Geographic. January 2002. page 2-12. 3. Raskin, Morris. The Origin of Dogs. 2003. http://www.dossu.org/dogs.html
4. Wayne, Robert and Savolainen, Peter. Multiple and Ancient Origins of the Domestic
Dog. Science. June 13, 1997, Vol 276, Issue 5319 pp 1687-9. 5. Morell, Virgina. The Origin of Dogs: Running with the Wolves. Science. June 13, 1997,
Vol 276, Issue 5319.
6. Wayne, Robert and Ostrander, EA. Out of the Dog House: The Emergence of the
Canine Genome. Heredity. April 2004, Vol. 92 Issue 4 p273. 7. Acland, GM and Ostrander, EA. The Dog that Came in from the Cold. Heredity. 2003.
8. Wang, Xiaoming. Origin and Evolution of Canidae. 2002. Natural History Museum of
Los Angeles County.
9. Jezierski, Chet. Evolution of the Dog. American Kennel Club.