| Summary: | We examined cognition and the development of social cognition in domestic dogs (Canis lupus familiaris) with three studies. Study one focused on numerical competence in dogs and studies two and three addressed the development of social relationships among littermates. In the first study, we examined the performance of dogs at quantity judgment tasks in two experiments. In experiment 1, we investigated the ability of 29 dogs to discriminate between two quantities of food presented in eight different combinations. We presented the choices simultaneously, and they were visually available to the subjects at the time of choice. In experiment 2, we tested two dogs from experiment 1 under three conditions of increasing difficulty. In condition 1, we used similar methods from experiment 1. In conditions 2 and 3, the food was visually unavailable to the subjects. In these later conditions, subjects had to keep track of quantity mentally in order to choose optimally. Dogs performed on par with apes given similar tasks. For the last two studies, we videotaped play behavior in four litters of domestic dogs to examine social development. Data collection occurred when the puppies were between 3 and 40 weeks of age, but collection times varied by litter. Early play-partner preferences were associated with preferences at older ages, and the tendency for puppies to prefer specific partners increased over time. Dyadic play was not symmetrical (i.e., puppies did not take turns being in the top and bottom roles), and as puppies matured, they initiated play with individuals they could dominate during play. Sex differences were observed for play initiations, offense behaviors, and self-handicapping. During third-party interventions in dyadic play, the intervening puppy targeted the dog receiving offense behaviors more often than the dog directing offense behaviors. Interveners did not selectively join (i.e., not target) preferred playmates, and they did not display reciprocity in joining. Intervention patterns suggest that puppies ...
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