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Dogs' Eyes Have Changed Since Humans Befriended Them
Bill Kristol@BillKristol·5h
"Dogs’ faces are structured for complex expression in a way that wolves’ aren’t, thanks to a special pair of muscles framing their eyes....Domesticated dogs may have evolved a specialized ability used expressly to communicate better with humans."
Link to tweet
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very interesting.
17 replies
= new reply since forum marked as read
= new reply since forum marked as read
The dog?human bond is unique and diagnostic of the evolution of human cultures. Dogs were domesticated over 33,000 y ago (1), and, during that time, selection processes have shaped both their anatomy and behavior and turned them into human’s best friend (2). The most remarkable among dogs’ behavioral adaptations, as a result of selection during domestication, is their ability to read and use human communication in ways that other animals cannot (3, 4). Dogs are more skillful in using human communicative cues, like pointing gestures or gaze direction, even than human’s closest living relative, chimpanzees, and also than their own closest living relatives, wolves, or other domesticated species (5). Recent research suggests that eye contact between humans and dogs is crucial for dog?human social interaction. Dogs, but not wolves, establish eye contact with humans when they cannot solve a problem on their own (6, 7). Eye contact also helps dogs to know when communication is relevant and directed at them, as dogs tend to ignore human pointing gestures when the human’s eyes are not visible (8, 9). Dogs, but not wolves, seem to be motivated to establish eye contact with humans from an early age (10, 11), and dogs’ motivation to establish eye contact with humans seems to be an indicator of the level of attachment between humans and dogs (12). Thus, mutual gaze between dogs and humans seems to be a hallmark of the unique relationship between both species during human cultural evolution.
Nagasawa et al. (13) showed that, between dogs and humans (but not wolves and humans), mutual gaze seems to lead to an oxytocin feedback loop analogous to the one that exists between human mothers and infants. Oxytocin has a fundamental role during affiliative behaviors in mammals and during the onset of maternal behavior and mother?infant attachment (14). Similarly, mutual gaze between dogs and humans seems to trigger an increase of oxytocin in both species, which then increases the motivation to establish eye contact (13). As this cross-species oxytocin loop can be found in dogs and humans, but not between dogs’ closest living relative (the wolf) and humans, selection processes during domestication must have played an important role whereby dogs hijacked the human caregiving response (15). The most likely evolutionary scenario is that dogs’ ancestor must have, to some extent, expressed characteristics that elicited a caregiving response from humans. Humans then consciously or unconsciously favored and therefore selected for those characteristics, leading to the analogous adaptations we see in dogs today.
Selection for traits that facilitate eye contact between dogs and humans might have, therefore, led to 1) anatomical differences in the facial musculature around the eyes between dogs and wolves and 2) behavioral differences between the species in terms of how they use these muscles to promote eye contact. We know that humans favor dogs that show paedomorphic (infantlike) anatomical features like a large forehead, large eyes, and so on; in studies asking people to select pictures presenting dog (or cat) faces, people prefer the faces that present paedomorphic features over others (16). Importantly, paedomorphic facial features can be even further exaggerated by facial muscle movements, which act to enhance the appearance of specific facial features (particularly the eyes). Waller et al. (17) showed that a specific facial muscle movement around the eyes (which they termed AU101: inner eyebrow raise) seems to be particularly attractive to humans. The movement makes the eyes appear bigger, hence more infant-like and potentially more appealing to humans. This inner brow raise also resembles a facial movement humans produce when they are sad, potentially eliciting a nurturing response from humans (17, 18). The study showed that dogs that produce this facial movement more were rehomed from a shelter more quickly than those that produced the movement less often, suggesting that the production of this eye movement gives dogs a potential selection advantage. No other facial movement had the same effect (17). However, thus far, it has been unknown whether domestication has shaped this phenomenon, and whether dogs show marked differences from wolves in anatomy and behavior in relation to this facial movement.
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Nagasawa et al. (13) showed that, between dogs and humans (but not wolves and humans), mutual gaze seems to lead to an oxytocin feedback loop analogous to the one that exists between human mothers and infants. Oxytocin has a fundamental role during affiliative behaviors in mammals and during the onset of maternal behavior and mother?infant attachment (14). Similarly, mutual gaze between dogs and humans seems to trigger an increase of oxytocin in both species, which then increases the motivation to establish eye contact (13). As this cross-species oxytocin loop can be found in dogs and humans, but not between dogs’ closest living relative (the wolf) and humans, selection processes during domestication must have played an important role whereby dogs hijacked the human caregiving response (15). The most likely evolutionary scenario is that dogs’ ancestor must have, to some extent, expressed characteristics that elicited a caregiving response from humans. Humans then consciously or unconsciously favored and therefore selected for those characteristics, leading to the analogous adaptations we see in dogs today.
Selection for traits that facilitate eye contact between dogs and humans might have, therefore, led to 1) anatomical differences in the facial musculature around the eyes between dogs and wolves and 2) behavioral differences between the species in terms of how they use these muscles to promote eye contact. We know that humans favor dogs that show paedomorphic (infantlike) anatomical features like a large forehead, large eyes, and so on; in studies asking people to select pictures presenting dog (or cat) faces, people prefer the faces that present paedomorphic features over others (16). Importantly, paedomorphic facial features can be even further exaggerated by facial muscle movements, which act to enhance the appearance of specific facial features (particularly the eyes). Waller et al. (17) showed that a specific facial muscle movement around the eyes (which they termed AU101: inner eyebrow raise) seems to be particularly attractive to humans. The movement makes the eyes appear bigger, hence more infant-like and potentially more appealing to humans. This inner brow raise also resembles a facial movement humans produce when they are sad, potentially eliciting a nurturing response from humans (17, 18). The study showed that dogs that produce this facial movement more were rehomed from a shelter more quickly than those that produced the movement less often, suggesting that the production of this eye movement gives dogs a potential selection advantage. No other facial movement had the same effect (17). However, thus far, it has been unknown whether domestication has shaped this phenomenon, and whether dogs show marked differences from wolves in anatomy and behavior in relation to this facial movement.
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https://www.pnas.org/content/early/2019/06/11/1820653116
we were completely in sync and had totally understanding of each other I truly believe. 🐕 
