The archaeological record indicates that man's best friend - the
domestic dog Canis familaris - was likely also its first
domestic animal. What though are its origins? Was it domesticated
once or did several events take place independent of one another?
Circumstantial evidence suggests that dogs have diverse origins.
During most of the late Pleistocene, humans and wolves co-existed
over a wide geographical area, providing ample opportunity for
independent domestication events and continued genetic exchange
between wolves and dogs. Indeed, the extreme phenotypic diversity
of dogs, even during the early stages of domestication, is highly
suggestive of a varied genetic heritage. Whilst this question
cannot be resolved through archaeological evidence, it is possible
that genetic evidence may, therefore, be able to help.
When portions of mitochondrial DNA from wolves and domestic dogs
was sequenced, the control region of wolves and dogs was
demonstrated to be highly polymorphic. The distribution of wolf haplotypes
displayed geographic specificity, with most localities containing
haplotypes unique to a particular region. Sequence diversity
amongst dogs was similar. However, mitochondrial haplotype
diversity in dogs could not be partitioned according to breed.
Many breeds shared sequences with other breeds. No dog sequence
differed from any wolf sequence by more than 12 substitutions,
whereas dog differed from coyotes and jackals by at least 20
substitutions and 2 insertions. This supported a wolf ancestry for
However, because mitochondrial DNA is maternally inherited,
interbreeding between female dogs and male coyotes or jackals
would not be detected. Therefore, a more limited study of nuclear
DNA was also carried out. This also supported the conclusion that
the wolf was the ancestor of the domestic dog.
Various methods of phylogenetic analysis distinguised four
distinct clades. Clade 1 included 19 of the dog
haplotypes. This group included representatives of many common
breeds, as well as ancient breeds such as the dingo, New Guinea
singing dog, and African basenji. Clade II included dog haplotype
D8, found in two Scandinavian breeds: the elkhound and jamthund.
This was also closely related to two wolf haplotypes found in
Italy, France, Romania and Greece. Clade III contained 3 dog
haplotypes, which were found in a variety of breeds such as the
German shepherd, Siberian husky, and Mexican hairless. Clade IV
also contained 3 haplotypes that were identical or very similar to
wolf haplotype W6 found in Romania and western Russia, which
suggests recented hybridisation between dogs and wolves.
Dog haplotype clades II and IV are most closely related to wolf
sequences from eastern Europe. The coyote and wolf sequences were
estimated as diverging one million years ago based upon the fossil
record. Consequently, this implies that the sequence divergence
between the most different genotypes in clade I (the most diverse
group) could have originated as much as 135,000 years ago. The
sequence divergence within clade I implies an origin of greater
than 14,000 years before present, which is what is indicated by
the archaeological record. Nevertheless, bones of wolves have been
found in association with those of hominids from as early as the
middle Pleistocene, up to 400,000 years ago.
It is suggested that early domestic dogs may not have been
morphologically distinct from their wild relatives. Conceivably,
the change from nomadic hunter-gatherer societies to more
sedentary agricultural population centres around 10,000 to 15,000
years ago may have imposed new selective regimes on dogs that
resulted in marked phenotypic divergence from wild wolves.
Although breeds show uniformity with respect to behaviour and
morphology, most breeds show evidence of a genetically diverse
heritage because they contain different haplotypes. Moreover, dog
sequences cluster with different groups of wolf haplotypes.
Therefore, after the origin of dogs from a wild ancestor, dogs and
wolves have continued to exchange genes.
Morey, D.F. 1994. The Early Evolution of the Domestic Dog. American
Scientist 82: 336-347
Vila, C.V., Savolainen, P., Maldonado, J.E., Amorim, I.R., Rice,
J.E., Honeycutt, R.L., Crandall, K.A., Lundeberg., Wayne, R.K.
1997. Multiple and Ancient Origins of the Domestic Dog. Science