Night vision & third eye(lids)
Last week, I was messing around with Midjourney, the AI image generator you can get access to via Discord. I noticed how consistently and badly it messes up eyes. One of the images I generated while trying to get character references for Irella (the protagonist of Civil Mage, which is currently being serialized and sent to financial supporters) reminded me of an African politician I used as a reference sketch for a different story I shared elsewhere... which inspired me to start learning more about eyes.
- I first learned about the phenomenon of being walleyed from a David Eddings book, but I somehow never investigated it beyond that until now. It not only refers to a condition (strabismus) where the eye looks outward from the nose, it can also refer to eyes with white corneas or irises.
- Some animals like mongooses, camels, and cats have nictitating membranes, which are also known as third eyelids. Humans have a vestigial version; sometimes it recurs in modern humans.
- Nocturnal bats have two spectral cone photoreceptor types for daylight and color vision. Incidentally, night time color vision is totally possible; nocturnal hawkmoths can see color at night, even if humans can't.
- The eye color of each species of raptor varies between yellow and brown, blue, gray, orange, and deep read. The eye color for raptors active during the day often varies with age.
- The human brain is best at processing visual signals at roughly sunset and sunrise; the twilight times. It's not because our eyes are better at perceiving light at this time, but rather, our circadian rhythms impact visual processing.
Although the Scandinavian Odin famously pledged his left eye in return for wisdom and knowledge, the motif of sacrificing an eye doesn't really appear in any other Scandinavian or Germanic myths. It does however appear in Irish myth. Saint Brigit deliberately blinded herself rather than be forced into marriage by her brothers, after they told her that no one with eyes as beautiful as hers could remain unwed (although really they just wanted the money they'd get from her groom). There are also a number of stories from various cultures about people who sacrifice their eyes miraculously regaining their vision: Irish Parallels to the Myth of Odin's Eye goes into greater depth and was worth the read if you enjoy mythology.
The "evil eye" is a supernatural belief in malevolent curses that exists in a lot of different cultures; it dates back at least five thousand years, particularly in the Mediterranean. Of particular interest to me is the Bedouin belief system, in which the evil eye, conveyed by folks looking upon you with envy and jealousy, can be responsible for a number of issues like breastfeeding issues, sexual impotency, colic, fatigue, etc. What I find particularly interesting is how many of the anti-evil-eye charms are really phallic; lots of horns, crab claws, shark teeth, keys, etc.
Eyes are unique to animals. On a technical level, they are "structures that break up environmental light according to its direction of origin." Organs with a single photoreceptor cell don't count. Spatial vision requires the ability to compare light intensities in different directions at the same time. Flatworms, larvae, and mollusks have simple pit eyes. More complex eyes with pinhole apertures and lenses are more effective, but my favorite example of eye-related sexual dimorphism is that in the case of the copepod Pontella, the single eye has a triplet lens in males, but only a doublet in females.
Blue eyes probably originated near the Black Sea about 10,000 years ago during the agricultural revolution. It's a mutation of the melanin production process and most likely only occurred once; pretty much everyone with blue eyes can trace their genetic history back to the same ancestor, and the mutation allowing it is always at the same spot in the genome. Weirdly enough, this mutation is associated with an increased likelihood of alcoholism.
📗 If you found this interesting, you may also enjoy the edition about avian combat, which touches on how starlings like to aim for their enemy's eyes.
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👀 Do you have a favorite story or fact involving eyes? Please reach out — I'd love to hear about it, either via email or in a comment where other readers can see.
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