Artificial vs. Natural Selection
 

       Today, it is clear that the evolution of the dog is being shaped by artificial selection because many dog breeders select dogs for certain working behaviours or, more often, a certain desired look. It is often assumed that humans domesticated dogs by taking wolf pups, taming them and selecting the best tempered wolves for breeding. Gradually, tamer, easier to handle "wolves" (dogs) were produced from this process. However, this may not have been the case, because how and why wolves became associated with human beings is not yet known. The archaeological record gives very little indication as to how the dog diverged from the wolf.  Debates on this topic often focus on the issue of intentionally, or whether or not humans consciously  began to breed wolves to produce dogs.  A scenario outlining how the dog may have evolved by a process of natural selection is described in detail by Coppinger and Coppinger (2000) and Budiansky (2000).  They point out that Palaeolithic and early Neolithic people would have been very unlikely to have raised young wolf pups as pets, since raising wolf pups is an extremely difficult and time consuming task.  Wolf puppies must be imprinted on humans starting at about 10 days to ensure that they are not afraid of humans as adults. Such a young puppy would need to be bottle-fed by humans, and pre-historic people probably would not have possessed the equipment needed to do it.  Domesticating wolves would have necessarily involved a huge number of wolves as well, and there is no evidence that Palaeolithic people ever kept large numbers of wolves.  For example, the experiment described above where domesticated silver foxes were produced in relatively few generations from a starting population of what were essentially wild foxes involved thousands of animals. It is unlikely that prehistoric people could have ever kept very many wolves captive in their settlements.

    The dog, then, may be a species that was the result of natural selection. A new "niche" was opened for animals about 10 000 years ago as some groups of humans began to settle into permanent settlements instead of living as nomads. Animals could live around these settlements and scavenge for food bits left around by people. Dogs may have "self-domesticated" when they started scavenging waste from the human settlements that began to appear at this time.  For any animal to succeed in such a niche, it would have to be comfortable living and eating in close proximity to humans, as an animal that feared them would not be able to survive in human settlements and would return to living away from people. Wild dogs that were less cautious around people than others may have began to live near humans, and natural selection would gradually produce "proto-dogs" from these animals that did not fear humans and could live in close proximity to them. Indeed, today in several parts of the world dogs do live like this.  Many villages across the world are home to dogs that live as scavengers and who are not intentionally cared for by humans. The first primitive dogs were likely very similar to these scavenging village dogs.

    These early canids that lived on the fringes of human society scavenging scraps may be the ancestor of early dog breeds.  These animals, which were already tame around humans, could be taken and used as hunting companions, or livestock guardians and different dog types likely evolved from these proto-dogs, not wolves.  Artificial selection by humans also further shaped the evolution of the dog, as dogs with traits desired by humans would have been better cared for than others, and would have been more likely to survive and breed.

Conclusion

    The dog, the world's oldest domesticate, is a very close relative of the grey wolf and the two species diverged anywhere from 135 000 to 14 000 years ago.  Molecular evidence has supported the former date while archaeological evidence supports the latter one. The fact that the dog originated from the wolf, a species with a distribution that spans Asia, North America and Europe, confounds any efforts to determine its origin. However, molecular and morphological evidence points to east Asia as a possible point of origin for the dog. The dog may also have been domesticated more than once. However, it seems that there was no separate domestication event in North America.

    Much of the diversity found in the domestic dog may be a result of a selection for tameness around people. The farm fox experiment started by Dr. Belyaev decades ago has demonstrated that selecting animals for a behavioural trait (such as a lack of fear of novel stimuli) effectively selects for animals with lower levels of adrenal hormones and higher levels of certain neurotransmitters (such as serotonin). Since these chemicals play a part in regulating the early development of an animal, selecting an animal for a behavioural trait could alter its development and thus its morphology.

    Although it is often assumed that the dog is a result of artificial selection, it is possible that early dogs evolved via natural selection. As humans began to form permanent settlements, a new niche was opened for animals to exploit.  They could steal and scavenge scraps from villages. To live in such a niche, an animal would have to be unafraid of people. Thus, wild dogs living in this niche would be selected for tameness around people.  This would alter the animals' morphology because, as stated above, selection for a behavioural trait selects for changes in hormones that regulate the development of the animal. These naturally tame "proto-dogs" could be the ancestor's of today's modern dog breeds.