Human proximity seeking in family pigs and dogs

Family dogs (Canis familiaris) seek human contact from an early age, can discriminate and prefer their caregivers over other humans. To investigate if being kept as a family animal is sufficient to induce similar early human proximity-seeking in another domestic mammal, here we directly compared such behaviours in dogs and similarly raised domestic pigs (Sus scrofa domesticus). We used a preference test to measure proximity-seeking behaviours of 4-month-old family pigs and dogs in the presence of their caregiver and either a stranger or a familiar object, in a novel environment. We found that both pigs and dogs preferred their caregivers over the familiar object but not over the stranger. However, when the caregiver and the stranger were present, only dogs showed an overall preference for human proximity, and pigs spent more time away from both humans. These results suggest that both dogs and pigs seek the proximity of their caregiver, but there is a difference in how each species generalizes their experience to other humans. Species-specific predispositions, including that dogs have a longer socialization period and that humans are more salient as a social stimulus for them, may be important for the early development of an overall preference for humans.