In order to reveal early species-specific differences, we observed the behavior of dog puppies (n ¼ 11) and wolf pups (n ¼ 13) hand raised and intensively socialized in an identical way. The pups were studied in two object-preference tests at age 3, 4, and 5 weeks. After a short isolation, we observed the subjects' behavior in the presence of a pair of objects, one was always the subject's human foster parent (caregiver) and the other was varied; nursing bottle (3 weeks), unfamiliar adult dog (3 and 5 weeks), unfamiliar experimenter (4 and 5 weeks), and familiar conspecific age mate (4 weeks). Dogs and wolves did not differ in their general activity level during the tests. Wolf pups showed preference for the proximity of the caregiver in two of the tests; Bottle-Caregiver at the age of 3 weeks and Experimenter-Caregiver at the age of 5 weeks, while dogs showed preference to the caregiver in three tests; conspecific Pup-Caregiver and Experimenter-Caregiver at the age of 4 weeks and dog-caregiver at the age of 5. Compared to wolves, dogs tended to display more communicative signals that could potentially facilitate social interactions, such as distress vocalization, tail wagging, and gazing at the humans' face. In contrast to dog puppies, wolf pups showed aggressive behavior toward a familiar experimenter and also seemed to be more prone to avoidance. Our results demonstrate that already at this early age-despite unprecedented intensity of socialization and the comparable social (human) environment during early development-there are specific behavioral differences between wolves and dogs mostly with regard to their interactions with humans.

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Background:The comparison of human related communication skills of socialized canids may help to understand the evolution and the epigenesis of gesture comprehension in humans. To reconcile previously contradicting views on the origin of dogs' outstanding performance in utilizing human gestures, we suggest that dog-wolf differences should be studied in a more complex way.Methodology/Principal Findings: We present data both on the performance and the behaviour of dogs and wolves of different ages in a two-way object choice test. Characteristic behavioural differences showed that for wolves it took longer to establish eye contact with the pointing experimenter, they struggled more with the handler, and pups also bit her more before focusing on the human's signal. The performance of similarly hand-reared 8-week-old dogs and wolves did not differ in utilizing the simpler proximal momentary pointing. However, when tested with the distal momentary pointing, 4-monthold pet dogs outperformed the same aged hand reared wolves. Thus early and intensive socialisation does not diminish differences between young dogs and wolves in behaviour and performance. Socialised adult wolves performed similarly well as dogs in this task without pretraining. The success of adult wolves was accompanied with increased willingness to cooperate.Conclusion/Significance: Thus, we provide evidence for the first time that socialised adult wolves are as successful in relying on distal momentary pointing as adult pet dogs. However, the delayed emergence of utilising human distal momentary pointing in wolves shows that these wild canines react to a lesser degree to intensive socialisation in contrast to dogs, which are able to control agonistic behaviours and inhibition of actions in a food related task early in development. We suggest a ''synergistic'' hypothesis, claiming that positive feedback processes (both evolutionary and epigenetic) have increased the readiness of dogs to attend to humans, providing the basis for dog-human communication.

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