Domestication constrains the ability of dogs to convey emotions via facial expressions in comparison to their wolf ancestors

Abstract

Dogs (Canis lupus familiaris) are the domestically bred descendant of wolves (Canis lupus). However, selective breeding has profoundly altered facial morphologies of dogs compared to their wolf ancestors. We demonstrate that these morphological differences limit the abilities of dogs to successfully produce the same affective facial expressions as wolves. We decoded facial movements of captive wolves during social interactions involving nine separate affective states. We used linear discriminant analyses to predict affective states based on combinations of facial movements. The resulting confusion matrix demonstrates that specific combinations of facial movements predict nine distinct affective states in wolves; the first assessment of this many affective facial expressions in wolves. However, comparative analyses with kennelled rescue dogs revealed reduced ability to predict affective states. Critically, there was a very low predictive power for specific affective states, with confusion occurring between negative and positive states, such as Friendly and Fear. We show that the varying facial morphologies of dogs (specifically non-wolf-like morphologies) limit their ability to produce the same range of affective facial expressions as wolves. Confusion among positive and negative states could be detrimental to human-dog interactions, although our analyses also suggest dogs likely use vocalisations to compensate for limitations in facial communication.

Keywords: Animal welfare; Domestic dogs; Domestication; Emotions; Facial expressions; Wolves.

Figure 1

Illustration of the differences in the main conveyers of facial expressiveness between wolf and examples of domestic dog breeds. (A) Wolf (Canis lupus) portrait depicting typical head morphologies and facial patterning. Note erect ears, head shape, fur length and slope, and facial masking as a consequence of lighter coloured ‘eyebrows’, muzzle and cheek area. Photograph by ER Hobkirk. (B) ‘Wolf-like’ Finnish Lapphund dog, with head morphologies and facial patterning almost identical to that of the wolf. Photograph by SD Twiss. (C) Typical Rottweiler face with conspicuous brown eyebrows (red circle), set against a solid black background. Note flopped ears and broad head shape in comparison with the wolf. Image courtesy of the American Kennel Club. (D) Brachycephalic face of a Pug dog. Note flopped ears, bulging eyes and excessive wrinkling in comparison with the wolf. Image courtesy of the American Kennel Club. (E) Komondor dog with less distinct facial features due to fur type (dreadlocks), length and slope. Image courtesy of the American Kennel Club.

Figure 2

Confusion matrix, showing the observed (actual) versus predicted affective states for wolf facial expressions (n = 559). Values within each true positive tile (diagonal) display the precision percentages per affective state. Overall precision = 71%.

Figure 3

Confusion matrix, showing the observed (actual) versus predicted affective states for dog facial expressions (n = 753). Values within each true positive tile (diagonal) display the precision percentages per affective state. Overall precision = 65%.