Unique morphology of the human eye and its adaptive meaning: comparative studies on external morphology of the primate eye

A Cross-species Comparison of Facial Morphology and Movement in Humans and Chimpanzees Using the Facial Action Coding System (FACS)

“…The most striking aspect of the translation process is the importance of contrast for the detection of facial movement; even when those facial movements are carefully studied, the lack of contrast makes the movement less salient in the chimpanzee. It has already been suggested that human eyes have more signal value than those of other primates (Kobayashi & Kohshima, 2001), but only gaze direction detection was considered and it is apparent that lack of scleral contrast also impedes the detection of facial actions in the eye region. While chimpanzees have larger more prominent brows than humans, movements of the brow are also enhanced in humans with the contrast against the hairless forehead (Campbell et al, 1999).…”

“…Thus, we can identify how and why a given facial movement may appear dissimilar across species in terms of underlying facial structure, musculature and surface coloration, and textures. As noted above, facial expressions interact with the underlying facial morphology to create salient signals; in primates, coloration or shape of facial features can emphasize or camouflage facial movements (Andrew, 1963;Kaplan & Rogers, 2002;Kobayashi & Kohshima, 2001;Napier & Napier, 1985;Preuschoft, 2000). For example, pigmentation of the upper eyelids in some species, or retention of hairy brows on hairless forehead in humans, may highlight actions of the brows Campbell, Benson, Wallace, Doesbergh, & Coleman, 1999;Preuschoft, 2000).…”

The origin of human multi-modal communication

“…For example, the toleration or indeed expectation of mutual gaze is of paramount importance in humans [56] but occurs less in other primates (e.g. [57], see also [58]), and the white sclera of the human eye has almost certainly evolved to enhance gaze detection [59]-remarkably, human infants are sensitive to the difference between direct and averted gaze from just 2-5 days after birth [60]. The rapid turn-taking despite indefinitely varying contents of turns is again without parallel; the sustained multi-modal deployment of vocal and visual signals on hands, face and body and the sheer amount of time and effort invested in communication seem without parallel among the other primates.…”

Liking products by the head of a dog: Perceived orientation of attention induces valence acquisition

“…It is telling in this regard that of all primates the human eye is the most conspicuous (Kobayashi & Kohshima, 2001), that human beings pay automatic attention to eye gaze (e.g., Friesen & Kingstone, 2003), and that deficits in joint attention are associated with the autism syndrom (e.g., Baron-Cohen, Wheelwright, & Jolliffe, 1997;Senju, Yaguchi, Tojo, & Hasegawa, 2003). Empirical evidence also suggests that Theory of Mind and joint attention phenomena generalize to communication in other species (e.g., Povinelli & Eddy, 1996) and to inter-species communication (e.g., Hare & Tomasello, 2005 To the best of our knowledge, only three recent studies are relevant to this issue.…”