Eye-white displays (starting with humans) and what we should call them, part 1

Everyone knows that in the human species the movements of the eyes can be expressive enough to outweigh the words spoken, e.g. when lies are being told. And that the sclera, i.e. the white of the eye, accentuates the tiny movements of the eyeballs, as if to spell out the unspoken messages in a rapid series of triangular flickers.

And many may have noticed that the selective breeding of the domestic dog has inadvertently made canine eyes more human-like in their expressions of emotion, partly by exposing the sclera (see https://www.wildculture.com/article/urban-rehab-humans-animals/1434 and https://i.kym-cdn.com/photos/images/original/001/363/236/ba2.jpg and https://abc13.com/dog-study-can-dogs-communicate-with-humans-eyes-intelligence/5351460/ and https://www.jsonline.com/story/news/2019/08/19/puppy-dog-eyes-dogs-evolved-eyebrow-muscle-help-bond-humans/1867592001/).

What is less-known is that our closest relatives among the primates are not only unlike us in this way, they are in some sense the antithesis. They have a sclera so pigmented that it seems adapted actually to hide intentions and emotions, keeping the eyes inscrutable (see https://www.americanscientist.org/article/do-the-eyes-have-it and https://www.researchgate.net/figure/Human-eyes-vs-chimpanzee-eyes_fig1_284308905 and https://www.nbcnews.com/id/wbna15625720 and https://www.facebook.com/CenterForGreatApes/posts/natsu-has-her-eyes-on-the-long-weekend-friyay-weekendvibes/10155916830732331/ and https://www.rgbstock.com/photo/r1OJLPk/The+Chimpanzee and https://www.sciencedirect.com/science/article/abs/pii/S1090513815000641).

And that the eyes of hyenas are more expressive in the human sense than those of most other animals.

And that those large mammals which we humans tend to regard as rather expressionless may have analogous systems operating about their ears, which are far more mobile than human ears and more relevant to the sensory priorities of the species involved.

In this initial Post I illustrate some of these points, helping to put our human eye-white displays into a broader biological context. In later Posts I will propose the term 'scleral semets' for the features of adaptive colouration involved in communication by means of 'eye language'. And, as if by digression, I will return to the subjects of my most recent Posts, namely the felids, to listen to their ear-language with new eyes.

The following show how pigmented the sclera is in chimpanzees and gorillas, as if to achieve the opposite of the facilitation seen in humans: https://www.smithsonianmag.com/science-nature/bonobos-teach-humans-about-nature-language-180975191/ and https://www.naturalworldsafaris.com/holidays/africa/congo/the-ultimate-gorilla-safari.

The following show the difference between the wolf, in which the sclera is tightly covered by the eyelids, and the domestic dog, in which the sclera is exposed: https://www.canstockphoto.com/wolf-eyes-7820377.html and https://depositphotos.com/85058888/stock-photo-close-up-on-dogs-eyes.html and https://www.theatlantic.com/science/archive/2019/06/domestication-gave-dogs-two-new-eye-muscles/591868/.

The following show how much more of the sclera is visible in hyenas than in the wolf or most wild canids: https://www.flickr.com/photos/tambako/12796302043 and https://www.istockphoto.com/video/brown-hyena-being-harassed-by-jackal-gm1138822949-304180773.

The following show that the cheetah, unusually for felids, displays the sclera in fear: https://www.photosincolor.com/wildlife-photographer-captures-amazing-photos-of-deadly-cheetah/.

Posted by milewski milewski, August 02, 2021 03:09


Posted by milewski 10 months ago (Flag)

The following shows how little of the sclera is visible in wolves: https://www.inaturalist.org/observations/48955

Posted by milewski 10 months ago (Flag)

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