Origin of the domestic dog or the result of natural introgression as the dog expanded across Eurasia. In 2018, a study found a small amount of dog ancestry in 62% of Eurasian wolf specimens looked at, that hybridization had occurred across a wide number of timescales and not just recently, however in contrast there was almost no admixture detected in the North American specimens. There was introgression of the male dog into the wolf, but also one hybrid detected which was the result of a male wolf crossed with a female dog. Wolves have maintained their phenotype differences from the dog, which indicates low-frequency hybridization.
Origin of the domestic dog could not be found in other dogs nor wolves today. As the taxonomic classification of the "proto-dog" Paleolithic dogs as being either dogs or wolves remains controversial, they were excluded from the study. The phylogenetic tree generated from mDNA sequences found a deep division between the Sarloos wolfdog and all other dogs, indicating that breed's recent deriving from the German Shepherd and captive gray wolves. The next largest division was between Eastern Asian dogs and Western Eurasian (Europe and the Middle East) dogs that had occurred between 14,000-6,400 YBP, with the Newgrange dog clustering with the Western Eurasian dogs. The