After researching why humans have white scleras when most primates have dark scleras, I stumbled upon the cooperative eye hypothesis. It proposed that white scleras may have evolved on behalf that it is an effective form of communication in that it makes the iris stand out and enables another to clearly see where the eye is looking so as to read expressions.

I noticed that dogs, which also have white scleras, use eye direction periodically for expression. Does the cooperative eye hypothesis apply to canines as well? If not, then for what reason might dogs utilize eye movement as they seem to do? Might such a thing be learned behavior?


It is hypothesized that the starkness of white sclera against darker colors of the pupil and iris is a unique mutation in primates that have become prevalent in human beings because it enhanced our ability to communicate with other humans and animals, including dogs, by more clearly communicating where we are looking.

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However, it has not yet been established that dogs use this communication with each other, communicating more commonly with other means such as body language, head direction, vocalizations, etc. Some dogs, especially domesticated ones, do have white sclera and it is proposed that this is due to unintentional selection by humans who have a preference for such features.

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What is extremely fascinating is that this 'mutation' occasionally occurs in chimpanzees and apes, too, but has not become prevalent in their respective populations.

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  • $\begingroup$ "it has been observed that dogs do not use this as communication with each other" I saw no evidence of this in your cited papers. Can you provide support for this claim? That is, after all, the OP's question. $\endgroup$ – anongoodnurse Feb 1 '15 at 18:33
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    $\begingroup$ His original question asked if the cooperative eye hypothesis applied to canines. $\endgroup$ – Anne Feb 1 '15 at 18:35
  • $\begingroup$ I'll clarify what I meant to say. $\endgroup$ – Anne Feb 1 '15 at 18:42

A new study published in the journal PLoS One compared facial characteristics, gazing behaviors, and sociality of 26 different canid species (including wolves, bush dogs, and Arctic foxes). The researchers found that animals with eyes and facial features that are easier to discern are more likely to live and hunt socially. (One of the authors, S. Kohshima, has studied the morphology of the human eye, its adaptive meaning, and has done comparative studies on external morphology of the primate eye.)

In this paper, the authors identified three face-eye types based on four contrast indices: the A-type, in which both pupil position in the eye outline and eye position in the face were conspicuous (11 species, including wolves and coyotes); the B-type, in which only eye position on the face was conspicuous (9 species, including the Fennec fox and jackals); and the C-type, in which both the pupil and eye position were inconspicuous (6 species, including the bush dog and the African wild dog).

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They compared group living vs. solo/pair living, group hunting vs. solo hunting, gaze duration and other parameters. Citing supporting evidence from other authors as well, they found that in species engaging in group living, 8 of 10 study species exhibit A-type faces. African wild dogs (C-type) use their white-tipped tails as visual signals, and like dingos, use vocalization, suggesting a developed acoustic communication. In contrast, gray wolves made almost no sound even during play or fighting but had more gazing behavior in more postures. Therefore, species with B- or C-type faces that in engage group living may use acoustic and/or other visual signals instead of the gaze signal as their primary means of communication (as is true for wolves and dogs). The enhanced gaze-signal of the A-type face could be disadvantageous during hunting, as prey animals could use the gaze signal to realize that they have been targeted by the predator and then prepare to escape. A-type faces were more common, then, in group hunting, where solo hunters were more commonly B or C-type faces.

In gray wolves, the gazing behavior (0.5s on average to humans, 3.32s average with up to 38s maximum with other wolves), termed conspecific with others of the same species, suggest that the gaze signal of gray wolves is mainly used for communication among conspecifics.

These results suggest that the facial color pattern of canid species is related to their gaze communication and that canids with A-type faces, especially gray wolves, use the gaze signal in conspecific communication... Our comparison of face morphology and gazing behavior among canid species highlighted the gaze-signal communication in species with A-type faces, especially gray wolves, and provided a novel perspective for studies on their communication and morphology.

Could the cooperative eye hypothesis apply to dogs as well? If not, then for what reason might dogs utilize eye movement as they seem to do?

Yes. (By the way, many dogs have white sclera.) The difficulty is that dogs are usually raised alone with humans and can lose the ability to "read" other dogs. One study, however, examined the behavior of dogs with human social cues (such as gazing) and conspecific (other dog) social cues. (Primates have been found to respond to conspecific social cues more than human gaze/pointing.) When the informant in this study (the one giving the cues) was an unfamiliar human, dogs responded well to gaze and gaze/pointing. However, when the informant was an unfamiliar dog (tethered, standing still, no human around to look at), the dogs were also able to follow the gaze of the informant dog, even when the body pointed elsewhere. Furthermore,

This skill with conspecifics is somewhat surprising because many of these domestic dogs had had only limited experience with other dogs. Indeed, the one intriguing developmental finding was that the 6-month old juvenile was only able to use cues produced by conspecifics, whereas two 4-year olds (the oldest in the sample) were only able to use human cues. ...it does suggest the hypothesis that many dogs are able to use conspecific gaze cues from early in life without extensive experience with conspecifics, and then ontogenetically, they extend this ability to humans (to some degree on the basis of similarities in human and dog facial features) as they interact with them - perhaps in some cases to the point that they lose their ability with conspecifics.

If more studies focused on conspcific cues among dogs instead of focusing on their interactions with humans, I think this behavior would be borne out and would be readily established.

A Comparison of Facial Color Pattern and Gazing Behavior in Canid Species Suggests Gaze Communication in Gray Wolves (Canis lupus)
Development of Gaze Following Abilities in Wolves (Canis Lupus) (interesting video)
Domestic Dogs (Canis familiaris) Use Human and Conspecific Social Cues to Locate Hidden Food
A Review of Domestic Dogs' (Canis Familiaris) Human-Like Behaviors: Or Why Behavior Analysts Should Stop Worrying and Love Their Dogs (just a cool paper)


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