Dog Ancestry and Behaviour
Dogs and wolves are clearly distinct in analyses of nuclear DNA.
Older Links with Wolves
A 2025 study in Proceedings of the National Academy of Sciences examined 2,693 published dog and wolf genomes for evidence of mixing between the two populations. The researchers combined methods for identifying local ancestry with analyses of nuclear genes, mitochondrial genomes and Y-chromosome sequences.
Wolf ancestry was detected in 64.1% of the modern breed dogs in the sample. The inferred mixing took place nearly a thousand generations ago on average, and the wolf ancestry now covered about 0.14% of those dogs' individual nuclear genomes.
Free-living village dogs formed another part of the analysis: all 280 of their genomes carried wolf ancestry.
No family tree built from a single nuclear gene grouped all dogs into one exclusive branch. Markers inherited through one parental line showed dog and wolf branches mixed together, and the resulting family trees did not all agree. The study also reported correlations between wolf ancestry and size, breed category and personality characteristics.
What the Genetic Tests Found
A separate Proceedings of the National Academy of Sciences study addressed genetic tests marketed for behavioural and personality traits, whose predictive accuracy had not been validated. It used data from Darwin's Ark, a community science initiative, covering more than 3,000 dogs with both genetic information and measurements of individual behaviour.
None of the candidate variants tested had the significant associations or predictive power for behaviour reported in earlier work. There were strong associations with visible physical traits, including height, leg length and ear shape.
The authors suggested that earlier studies using breed-average behaviour, rather than measurements for individual dogs, had been confounded by population structure. They described behaviour as complex and involving many genes, beyond what a test considering only a few variants can accurately predict.
Breed and Early Experience
In a study published in Scientific Reports, English-speaking guardians provided information on 4,497 dogs. They reported life histories and current living environments, and rated behaviour using the Canine Behavior Assessment and Research Questionnaire, known as C-BARQ.
Adverse experiences during the first six months, including abuse and relinquishment, were significantly associated with greater fearfulness and aggression in adulthood. The association remained after the analysis accounted for acquisition source, sex and neuter status.
The relationships between adversity and fearful or aggressive behaviour varied systematically by breed. The authors suggested that heritable factors might contribute to vulnerability and resilience.
Breed Labels and Adoption Impressions
An Animal Welfare study of adoption impressions described mixed-breed dogs as the majority in US animal shelters. Many shelters still assigned breed labels by appearance, despite research indicating that visual identification was largely inaccurate. Some included personality descriptions alongside breed labels or instead of them.
The experiment recruited participants at a shelter and online, showing them ten dog photographs and asking how likely they were to adopt each dog. Photographs appeared randomly in four forms: alone, with a breed label, with a description, or with both. Overall, descriptions significantly increased perceived adoptability, while breed labels decreased it.