The origin of the domestic dog, Canis familiaris, has been a source of confusion and controversy for many years. Currently, the hypothesis favored by the majority of researchers is the origination of dogs from the gray wolf, Canis lupus, but even that position has been challenged in the past. Yet, for the most part, morphological and molecular data have consistently supported this hypothesis. Dogs and gray wolves share unique allozyme alleles, highly polymorphic satellite alleles, and an extremely similar if not identical mitochondrial DNA (Ruvinsky and Sampson, 2001). Recent genetic studies have even shown that domestication from wolves may have occurred during multiple, independent events and that taming could have begun over 100,000 years ago (Vila and Wayne, 1999). The precise timing of domestication is not easy to resolve since domestic dogs were most likely not distinctive enough to be told apart from wolves until the advent of artificial selection (Ruvinsky and Sampson, 2001). Based on current archeological evidence, the first record of true domestic dogs occurs in the Middle East and dates to around 12000-14000 years ago (Ruvinsky and Sampson, 2001).

Certainly there are remains nearly as old in Europe, North America, and other parts of Asia. The question may no longer be from what species did Canis familiaris arise, but where and how. Morphological comparisons have suggested that domestic dogs most closely resemble the Chinese subspecies Canis lupus chanco (Olsen, 1985). This small wolf does seem a likely candidate, but other studies provide evidence that origination did not come from only one event or lineage. Current research has shown that the different breeds of domestic dog group into four distinct lineages, or clades, and that each group has its own independent connection to Canis lupus (Leonard et al., 2002; Ruvinsky and Sampson, 2001). This assessment seems probable and long before those results were obtained workers had assumed that New World domestic dogs had evolved from North American gray wolves while Old World breeds had developed independently from Eurasian counterparts. Surprisingly, this theory may need to be revised. Not only did Leonard et al. (2002) discover evidence that Canis familiaris is composed of multiple lineages, but also that the majority of New World 'native' breeds actually map onto several 'Old World' clades. Very few breeds turn out to be derived from North American gray wolves. It would appear that more than one Eurasian variety of domestic dog crossed into North America along with humans thousands of years ago. This may not, however, have been the only introduction of European genes, as colonists were reluctant to uphold the pure breeds native to the New World when they began settlement in the 15th century.

This specimen was made available to The University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Timothy Rowe of The University of Texas at Austin courtesy of the Texas Memorial Museum. Funding for scanning was provided by a National Science Foundation grant.

Dorsal view	Lateral view

Ventral view	Dorsal view

This specimen was scanned by Matthew Colbert on 5 January 2005 along the coronal axis for a total of 645 slices. Each 1024x1024 pixel slice is 0.1439 mm thick, with an interslice spacing of 0.1439 mm and a field of reconstruction of 68 mm.

Literature

Leonard, J. A., R. K. Wayne, J. Wheeler, R. Valadez, S. Guillén, and C. Vilà. 2002. Ancient DNA evidence for Old World origin of New World dogs. Science 298:1613-1616.

Miller, M. E. 1993. Miller's Anatomy of the Dog, 3rd edition. Howard E. Evans, (ed.), W.B. Saunders Company, Philadelphia, 1113 pp.

Olsen, S. J. 1985. Origins of the Domestic Dog. The University of Arizona Press, Tucson, Arizona, 118 pp.

Ruvinsky, A., and J. Sampson. 2001. The Genetics of the Dog. CABI Publishing, New York, New York, 564 pp.

Vilà, C., and R.K. Wayne. 1999. Hybridization between wolves and dogs. Conservation Biology 13:195-198.

None available.