The Domestication Hypothesis for Dogs• Skills with Human Communication

Animal Behaviour 79 (2010) e1–e6 Contents lists available at ScienceDirect Animal Behaviour journal homepage: www.elsevier.com/locate/anbehav Forum Articles The domestication hypothesis for dogs’ skills with human communication: a response to Udell et al. (2008) and Wynne et al. (2008) Brian Hare a,*, Alexandra Rosati a, Juliane Kaminski b, Juliane Braüer b, Josep Call b, Michael Tomasello b a Department of Evolutionary Anthropology & Center for Cognitive Neuroscience, Duke University, Durham, NC, U.S.A. b Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany article info Article history: Received 7 February 2009 Initial acceptance 15 June 2009 Final acceptance 25 June 2009 Available online 29 August 2009 MS. number: AF-09-00115R Keywords: cognitive evolution dog cognition domestication social cognition Domestic dogs have special skills in comprehending human puppies and must be explicitly trained to express dog-like skills in communicative behaviours (Hare & Tomasello 2005; Miklosi 2008). response to human communicative cues (Agnetta et al. 2000; Hare Dogs across a range of breeds use human communicative cues such et al. 2002; Viranyi et al. 2008). This conclusion holds even for as pointing or physical markers to find food that is hidden in one of wolves reared in identical conditions with a group of dogs for the two hiding places (controls rule out the use of olfactory cues; purpose of comparing their social skills with humans. In summary, Cooper et al. 2003; Hare & Tomasello 2005; Miklosi & Soproni it is unlikely that dogs simply inherited their unusual skills from 2006). In direct comparisons, dogs are even more skilled than their last common ancestor with wolves (Viranyi et al. 2008). chimpanzees at using human communicative cues when searching Additionally, dogs develop their ability to use human commu- for food (Hare et al. 2002; Braüer et al. 2006). Moreover, a number nicative cues, such as pointing cues or gaze cues, as young puppies of studies suggest that dogs understand human gestures commu- regardless of rearing history. Even puppies as young as 6–9 weeks nicatively, as a number of possible low-level explanations have of age can use a human’s communicative cues, including unadopted been ruled out (e.g. only responding to movement; reflexively co- puppies still living with their littermates and having little exposure orienting; using only familiar cues, etc.; Hare et al. 1998; Agnetta to humans beyond routine care (Hare et al. 2002; Riedel et al. 2008; et al. 2000; Soproni et al. 2001; Miklosi 2008). Viranyi et al. 2008). This suggests that dogs’ use of human The sophistication that dogs show in using human communi- communicative cues does not require extensive exposure to cative cues led researchers to investigate the origins of these abil- humans (e.g. Hare et al. 2002). ities and to conclude that these social skills are not simply inherited These two major findings led researchers to explore the possi- from wolves nor are they simply learned as a result of exposure to bility that dogs evolved their unusual ability to use human humans in ontogeny, but rather they have evolved as a result of communicative cues not only during, but as a direct result of, domestication (Hare & Tomasello 2005). Although wolves can domestication (Miklosi et al. 2003; Hare & Tomasello 2005). potentially learn to use human communicative cues (much like Comparisons between experimentally domesticated foxes and nonhuman primates), they do not show these skills as young a matched control line of foxes support the hypothesis that domestication, or selection against aggression towards humans, can, as a by-product, lead to enhanced skills in comprehending human gestures. Experimental foxes bred over 40 generations to * Correspondence: B. Hare, Department of Evolutionary Anthropology & Center for Cognitive Neuroscience, Duke University, Durham, NC 27708, U.S.A. approach humans without fear were more skilled at using human E-mail address: [email protected] (B. Hare). gestures than were control foxes that were not bred over the same 0003-3472/$38.00 Ó 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.anbehav.2009.06.031 e2 B. Hare et al. / Animal Behaviour 79 (2010) e1–e6 period for their reaction to humans. Crucially, the control and (2008), were tested by caregivers in familiar outdoor enclosures, experimental foxes participated in the experiments at similar levels but unlike in Hare et al.’s (2002) study, the caregiver in Udell et al.’s (i.e. made equal numbers of choices within test sessions) and, when (2008) study tested the wolves while standing inside the subjects’ tested with a nonsocial cue, the control foxes were actually more enclosure. Three of the dog groups consisted of family-reared pet skilled than the experimental foxes, effectively ruling out the dogs that were tested by different combinations of familiar or possibility that the control foxes were too fearful or unmotivated to unfamiliar experimenters and testing locations: dogs in the ‘home participate in all human-led tasks (Hare et al. 2005). The findings unfamiliar’ group were tested at their homes by an experimenter; from these experiments with foxes provide further support that the dogs in the ‘outdoor familiar’ group were tested in a less familiar domestication of dogs actually enhanced their ability to use outdoor location by a familiar human; and dogs in the ‘outdoor communicative cues provided by humans. unfamiliar’ group were tested in a less familiar outdoor location by Recently, two papers challenge the ideas (1) that dogs outper- an experimenter. The final group consisted of dogs living at a local form wolves in using human communicative gestures (Udell et al. shelter that were tested in a less familiar room by an unfamiliar 2008) and (2) that dogs require very limited human exposure to human experimenter. show initial skill in using such communicative cues (Wynne et al. Unlike all previous studies, Udell et al. (2008) gave subjects four 2008). In the first of these studies, Udell et al. (2008) present warm-up trials in which they placed food on top of one of two findings suggesting that wolves are more skilled than dogs in using hiding locations in view of subjects so that, once placed, the food human communicative cues in a food retrieval task. Specifically was visible to the subject (usually in a warm-up phase with they found that wolves were more skilled than shelter dogs and pet primates or dogs, food is hidden under different hiding locations as dogs tested outdoors, and equally as skilled as pet dogs tested the subjects watch). During this warm-up, food was always indoors. In a second study, Wynne et al. (2008) critiqued an completely visible and all subjects correctly retrieved the visible experiment by Riedel et al. (2008) that examined the use of human food in all four trials. After the warm-up, all subjects were then communicative cues by dog puppies. Riedel and colleagues repor- given 10 experimental test trials. However, the methodology used ted a series of three studies showing that domestic dog puppies in the test trials was very different from that of previous studies. In comprehended a human pointing gesture as early as 6 weeks of age. Udell et al.’s (2008) study, no food was hidden, but rather the Wynne and colleagues suggest that this study did not rule out the experimenter pointed and ‘when a subject indicated a correct possibility that human experience plays a decisive role. In both choice, the experimenter clicked [a clicker device] and then drop- papers this team of authors claims that their evidence and rean- ped a piece of food on the chosen container’ (page 3). This task alysis refute the domestication hypothesis, and they suggest that differs greatly from the traditional method in which a human differences among canid species in social skills is largely due to indicates the location of hidden food to a dog (reviewed in: Hare & environmental factors during rearing rather than being a result of Tomasello 2005; Miklosi 2008). dog domestication. The performance of each individual subject was compared to To evaluate the evidence presented in these studies, we first chance using binomial probabilities (authors assigned chance to discuss several methodological concerns that we have about the 50%), one-sample t tests, one-way ANOVAs and post hoc compar- approach of Udell et al. (2008), then we reanalyse their data based isons (Bonferroni tests). In addition to the experimental trials, after on these methodological concerns. We also present a test of shelter every second experimental trial, a control trial was run that was dogs naı¨ve to cognitive testing to examine whether it is the case identical to the experimental trial with the exception that no that shelter dogs are less skilled at using human communicative pointing cue was provided (these trials acted as control for olfac- cues than other groups of dogs. Finally, we directly rebut the tory cues that the subjects might be using). Unlike other studies, if critique of Wynne et al. (2008) and argue that there remains no subjects made incorrect choices for more than three trials consec- evidence of significant differences in performance between dogs of utively they were given another warm-up trial in which food was different ages in their use of human communicative cues. We placed on one of the two hiding locations as the animal watched; conclude that the domestication hypothesis remains the best this was done to rule out the possibility that the subjects’ failures explanation for dogs’ special skills for communicating with were due to lack of food motivation. humans. Based on their analysis of the data, Udell et al. (2008) concluded that the performance of the five groups of subjects differed REANALYSIS OF UDELL ET AL.

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