In the current study, we found that wolves and dogs differed in their ability to delay gratification in an exchange task administered by a familiar human person. While both adult wolves and adult dogs could delay gratification in a quality condition, dogs outperformed wolves with tolerating a mean delay of 66 s compared to 23 s. There are a few interesting aspects of this study that warrant further discussion.

Comparing our dog results with previously published research on dogs, while one dog in each study tolerated similarly high delays, the mean delay tolerated by our dogs was almost twice as long as the one reached by the 12 pet dogs in Brucks et al. (2017b) study. Interestingly, in the pet dogs, there was a very high variance between individual dogs with 7 of the 12 dogs waiting only up to 20 s. In our smaller sample, variance was rather small with all five dogs waiting at least 45 s (and seven of eight wolves waiting at least 20 s). There are two possible, likely additive explanations for this difference between the two studies. Firstly, our animals at the Wolf Science Center are kept under more standardized conditions (including the training procedures and life experiences) than pet dogs that receive individualized training by their owners and have vastly variable life experiences. Secondly, we tested the animals face to face with one of our animal trainers, while in the study with pet dogs the experimenter and owner were hidden behind a cover and not visible during the test. Thus, our dogs might have perceived our set-up more as an obedience task compared to the pet dog studies, which could, in connection with the standardized training in our facility, lead to higher social inhibition (see Range et al. 2019; Udell 2015), which in this paradigm would seem like better self-control. A similar explanation has also been put forward to explain the long delays tolerated by the pet dogs in the study of Leonardi et al. (2012), in which two of the five participating dogs belonged to the experimenter and were tested face to face, in comparison to the pet dogs in Brucks et al. (2017b).

Interestingly, this latter explanation could, at least partly, also explain the difference we observed between wolves and dogs in this paradigm, with dogs clearly tolerating longer delays than wolves. While both wolves and dogs are very attentive and cooperative towards humans, dogs follow the lead of the humans more than wolves, suggesting that dogs might have been selected for increased submissive inclinations (Deferential Behaviour Hypothesis, Range et al. 2019) to minimize conflicts. A potential difference in submissiveness, especially towards humans, could, in our task with the human experimenter possessing the food and directly facing the animal, lead to better social inhibition/self-control in the dogs than the wolves. Interestingly, also in the other studies where the dogs outperformed wolves in terms of inhibitory control, humans interacted with the animals by constraining them (pointing: Gácsi et al. 2009a, b) or repeatedly demonstrating an action (cylinder task: Marshall-Pescini et al. 2015). In contrast, when the animals were tested in more asocial settings (detour task: Marshall-Pescini et al. 2015; inhibitory control battery: Brucks et al. 2019) or where the animal needed to wait for a conspecific partner (Marshall-Pescini et al. 2017), wolves did at least as well as if not better than dogs (see also Ostojić and Clayton 2014). However, when comparing the wolves’ performance with the performance of the pet dogs in the more asocial delay of gratification task (Brucks et al. 2017b), the dogs still outperform the wolves with 5 of the 12 dogs waiting for more than 20 s and as a group, tolerating a mean delay of 35.6 s. Interestingly, the variance of the pet dogs in this self-control task is rather high, and it would be important to know whether the dogs that performed better had some additional training allowing them to tolerate higher delays. Also, while the owner and experimenter were not in visual contact during testing, they were both present in the room and thus could have still influenced the behaviour of the pet dogs, especially if extensively trained.

Thus, two factors might influence the results in our task. On the one hand, self-control abilities of wolves and dogs might indeed vary. On the other hand, social and non-social inhibition might potentially be separate constructs, with domesticated species likely being stronger socially inhibited by humans than non-domesticated species (Brucks et al. 2019). Unfortunately, the current study was run before the more recent ones and the chosen set-up does not allow us to differentiate between these two possibilities. However, independently of the reason, the behaviour of dogs being more self-controlled in the presence of the humans, is likely one reason, why dogs make better pets than wolves.

Another possibility, why wolves performed worse compared to dogs in this task, is their much higher activity level. Several studies have shown that wolves are more explorative and active than dogs (Rao et al. 2018a, b), potentially making it difficult for the animals to inhibit manipulating the apparatus. Also in this task, wolves were more active than the dogs (wolves 50.4 ± 16.8% and dogs 17.3 ± 17.4% of delay time active). The dogs’ inactivity could potentially be explained by them being socially inhibited by the human if indeed dogs see the situation as an obedience task, as suggested above. This would also explain why the dogs’ success increased when being less active. For the wolves, in contrast, there was no effect of locomotion on the wolves’ ability to delay gratification (see Table 5 for summary of results).

Both dogs and wolves used variable, albeit partly different, strategies to distract themselves during the delay periods. Dogs and to a lesser degree wolves did look away from the food, as has been reported also for other species including children (Mischel and Ebbesen 1970), chimpanzees (Evans and Beran 2007), a grey parrot (Koepke et al. 2015) and pet dogs (Brucks et al. 2017b). Moreover, wolves alternated their gaze between the high- and low-value reward, which increased their success (see Table 5 for summary of results). This points to wolves paying very close attention to what is happening when they are actually looking. It has already been proposed that the wolves pay attention to details more than dogs (Range et al. 2014; Range and Virányi 2014). Interestingly, though the animals would have been able to distract themselves in our set-up by approaching and trying to interact with the familiar person who was holding the camera, neither dogs nor wolves used this option even once but completely ignored that person. This is interesting since chimpanzees have been reported to engage in self-distracting behaviours and interact with toys when giving the option to increase their waiting times (Evans and Beran 2007). It is possible that our animals did not use this option since they are used to people filming and not interacting with the animals during that time from other studies.

One more interesting difference that emerged between wolves and dogs is how they reacted to the motivation trials, in which the animals only had to wait for 2 s. Wolves performed overall worse than the dogs even in the motivation trials when the delay was very short. However, the performance of the wolves in the motivation trials did not decrease as the delays got longer in the associated delay trials, whereas this was the case with the dogs. These different patterns might indicate that the wolves had a lower motivation than the dogs to participate in the task from the beginning on, which might explain their worse performance in the delay trials compared to the dogs, whereas the dogs only lost their motivation with longer delays.

Alternatively, it is possible that the dogs and wolves were similarly motivated to participate in the task and their different performance in the motivation trials rather indicates that the wolves understood the task better in the sense that they learned that there are two kinds of trials: one type has very short waiting times worth waiting for and another type, where you have to continue waiting for longer times. Thus, it might be worthwhile to wait at least for 2 s, even if you do not want to wait for a long time. The imperfect performance of the wolves in the motivation trials might indicate a lack of inhibitory control, which might be reduced in the dogs due to the presence of the human (see above). However, if the wolves differentiated between the two trials, this could have also influenced their overall performance, since, with the strategy of waiting at least 2 s, they would be successful in at least half of the eight total trials, while not facing the frustration of having to wait in the longer delay trials. Moreover, by not waiting in the longer delays but in the motivation trials, they actually increased their reinforcement rate. Thus, the wolves might have employed a different, more beneficial strategy to cope with the task, explaining their worse performance in comparison to the dogs in the delay of gratification. This is a limitation in the study design that we did not anticipate and further studies should investigate, whether wolves and dogs indeed differ in how they take the reinforcement rate into account when faced with such tasks.

Finally, the fact that none of the animals—not even the wolves—differentiated between the different reward types is not very surprising in hindsight. We recently conducted a study on the food preferences of wolves and dogs and realized that neither the wolves nor dogs express a preference for meat over sausage in a two-choice task, but that they prefer both sausage and meat over dry food (Rao et al. 2018a, b).

Overall, our results offer different explanations to why dogs waited longer than wolves in this task. First, dogs are indeed better at delaying gratification than wolves at least if a human is present. This is probably best explained by direct selection for social inhibition during the process of domestication (deferential behaviour hypothesis). It would be interesting to investigate whether the dogs and the wolves would perform more similarly if the task would be conducted in an asocial manner. Second, it is also possible that the animals had a different motivation to participate in the task or third, a different understanding of the task contingencies. Future studies need to disentangle these different explanations.