Geneticists who compared the genes of large dogs, small dogs and wild relatives, found a version of a gene that is carried by all small dogs and very few of the others, apart from grey wolves in the Middle East, suggesting that today's small domesticated dogs evolved from them.
The study was led by evolutionary geneticist Melissa Gray of the University of California, Los Angeles, and a paper on it appeared online in the journal BMC Biology on 24 February.
Previous studies on the origins of the domestic dog have used mitochondrial DNA, which is passed on only through the mother. These suggest that the domesticated dogs we see today originate from animals that lived between 5,000 and 16,000 in East Asia. However, archaeologicists digging in Europe and the Middle East have found evidence that suggests domestic dogs were already around 31,000 years ago....
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I found this pretty interesting; the chihuahua's come a long way eh?