Ocular displays and what we should call them, part 2

...continued from https://www.inaturalist.org/journal/milewski/54887-ocular-displays-starting-with-humans-and-what-we-should-call-them-part-1#

The human species uses 'eye-language'. This works partly because the sclera (https://en.wikipedia.org/wiki/Sclera) is paler than the iris, the eyelids, and the eyebrows.

'Adaptive colouration' is involved. This is because, without some degree of pale/dark contrast, the subtle shiftiness of the eyeballs would hardly be visible, even at conversational distances.

In a previous Post, I coined the term 'semet' for any feature of adaptive colouration that is too small-scale to be conspicuous to scanning predators, but conspicuous enough at close quarters to aid social communication.

Human scleral displays are therefore, in principle, similar to the many other small-scale, social (intraspecific) displays found in various other mammals.

Any scientific terms should be aligned accordingly. The category of displays being discussed here is 'ocular semets'.

According to this approach, could we agree that Homo sapiens possesses a 'scleral semet', as part of our adaptive colouration?

To see how hidden the eyes of apes are by pigmentation of the sclera, compare

Ocular semets are relatively poorly-developed in apes, although a scleral semet occurs in some individuals of Gorilla, and juveniles of Pongo have pale emphasis on the skin below the eyes.

By contrast with apes, several species of monkeys resemble humans to various degrees, in possessing scleral semets:

Classification and interpretation of ocular semets in apes and monkeys is complicated.

This is partly because

There thus arises a distinction between scleral semets and other types of ocular semets.

I suggest the term 'palpebral semets' for the displays of pale eyelids seen in various monkeys.

Certain species of baboons (Papio and Theropithecus) exemplify this. The sclera is pigmented and inconspicuous. However, the upper eyelids are pale, and displayed by exaggerated blinking.

The following show palpebral semets in baboons:
Papio ursinus: https://www.gettyimages.co.uk/detail/photo/large-male-chacma-baboon-displaying-its-eyelids-in-royalty-free-image/617783947?adppopup=true
Papio anubis: https://fineartamerica.com/featured/close-up-of-an-olive-baboon-papio-animal-images.html.

Compare the above with the obfuscation and inscrutability in the following of Papio ursinus:
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.

The only species of baboon showing a scleral semet seems to be Papio hamadryas: https://www.canstockphoto.com/close-up-portrait-of-male-hamadryas-38469311.html and https://www.gettyimages.co.uk/detail/photo/hamadryas-baboon-face-close-up-looking-away-royalty-free-image/1347246473?adppopup=true.

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

Comments

Eye language is quite important for hominid and cercopithecid primates, as with primates in general. As far as it's known, Glires (Rodentia+Lagomorpha), which in question is sister to the Euarchonta (Scandentia, Dermoptera, Primates) don't possess the same level of dependence on eye communication as primates. Appreciate the quality of the sources @milewski

Posted by paradoxornithidae about 2 years ago

https://www.mogenstrolle.com/primates

Posted by milewski about 1 month ago

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