Eye-white displays and what we should call them, part 2

In the human species, eye-language works partly because the sclera is paler than the iris, the eyelids, and the eyebrows. 'Adaptive colouration' is involved, because without some degree of pale/dark contrast the subtle shiftiness of the eyeballs would hardly be visible even at conversational distances. Human scleral displays are therefore in principle similar to the many other small-scale social (intraspecific) displays found in various other mammals; and a scientific term should be aligned accordingly.

In a previous Post, I coined the term 'semet' for any feature of adaptive colouration which is too small-scale to be conspicuous to scanning predators, but conspicuous enough at close quarters to aid social communication. According to this approach, could we say that the human species possesses a 'scleral semet'?

To see how hidden the eyes of apes are by pigmentation of the sclera, compare https://www.alamy.com/stock-photo-orangutan-pongo-pygmaeus-close-up-of-the-face-49328105.html with the albino version https://www.independent.co.uk/news/world/asia/albino-orangutan-rare-borneo-blonde-hair-blue-eyes-central-kalimantan-region-indonesia-borneo-survival-foundation-a7715836.html; and compare https://www.istockphoto.com/photo/close-up-of-a-male-western-gorilla-gm892726338-247038308 with https://i.redd.it/3p9hflrl0h261.jpg.

Although the apes generally lack any scleral semet, several species of monkeys resemble humans in this way: https://www.sciencephoto.com/media/1091429/view/tibetan-macaque-eyes and https://www.gettyimages.com.au/detail/photo/southern-or-sunda-pig-tailed-macaque-mature-male-royalty-free-image/591073170?adppopup=true and https://www.gettyimages.com.au/detail/photo/portrait-of-a-lion-tailed-macaque-macaca-silenus-royalty-free-image/1016151852 and https://paychecksforlife.blogspot.com/2020/11/monkey-with-blonde-hair.html and https://mycbs4.com/news/local/gallery/jungle-friends-primate-sanctuary-searching-for-escaped-capuchin-monkey-near-gainesville?photo=1#photo-2 and https://www.monkeysanctuary.co.za/capuchin-monkey and

Interpretation of scleral semets in monkeys is complicated not only because the phylogenetic sprinkling of these species seems so random but also because monkeys have other semets in which it is the eyelids that are conspicuously pale (https://www.agefotostock.com/age/en/details-photo/northern-pig-tailed-macaque-macaca-leonina-portrait-with-eyes-closed-thailand-khao-yai-national-park/BWI-BS373272). There thus arises a distinction between scleral semets and other types of ocular semets.

Certain species of baboons (Papio) exemplify this because they have pigmented, inconspicuous scleras but pale upper eyelids that are displayed by exaggerated blinking. Compare https://fineartamerica.com/featured/close-up-of-an-olive-baboon-papio-animal-images.html with https://www.freepik.com/free-photo/closeup-shot-baboon-monkey-with-blurred-background_12305937.htm and the more revealingly illuminated https://www.shutterstock.com/nb/image-photo/close-shot-baboon-sitting-grass-1988070962.

Posted by milewski milewski, August 02, 2021 10:12


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