A genetic study of grey wolves has found that small domesticated dogs probably originated in the Middle East more than 12,000 years ago.

Sadie the Scottish terrier, winner of best in show at the 2010 Westminster Dog Show, can trace her origins to grey wolves in the Middle East. (Henny Ray Abrams/Associated Press) Researchers at the University of California examined the history of a gene, called IGF1, in grey wolves and in large and small breeds of dog.

They found that the version of the gene that in large part determines small size in dogs probably originated in dogs with the ancient domestication of grey wolves in the Middle East.

"Our results show that the version of the IGF1 gene found in small dogs is closely related to that found in Middle Eastern wolves and is consistent with an ancient origin in this region of small domestic dogs," said evolutionary biologist Melissa Gray, in a statement.

Gray said the mutation that gave rise to the small-sized variation of the gene came after the first domestication of the dog, but dogs and wild wolves continued to interbreed even after domestication.

"Because all small dogs possess this variant of IGF1, it probably arose early in their history," said Grey.

The researchers' previous work unexpectedly found that some very large breeds, such as mastiffs, bullmastiffs, and rottweilers, also have the "small" version of the gene.

Archeologists have found remains of small dogs in the Middle East dating to 12,000 years ago. Older remains of domesticated dogs in Germany and Western Russia are all of large dogs.

Gray said artificial selection for small size is a common theme in domestication of animals, seen in cattle, pigs and goats, as well as dogs.

"Small size could have been more desirable in more densely packed agricultural societies, in which dogs may have lived partly indoors or in confined outdoor spaces," said Gray.