(C) Daily Kos This story was originally published by Daily Kos and is unaltered. . . . . . . . . . . Top Comments: Evolution of Vision in Vertebrates. [1] ['Thom Hartmann', 'Mother Mags', 'Bill In Portland Maine', 'Wafflehacker Aka Joshhacks'] Date: 2026-08-07 Uploaded to DailyKos by Ed Tracey Here at Top Comments we strive to nourish community by rounding up some of the site’s best, funniest, most informative commentary, and we depend on your help!! Here’s how to submit nominations in DK6: If you see a comment by another Kossack that deserves wider recognition, please send it either to topcomments at gmail dot com or via kosmail to topcomments- either search for user @topcomments, or click that link then click “send message”!) by 9:30pm Eastern for inclusion in that day’s diary. Please, please include a few words about why you sent it in as well as your user name (even if you think we know it already :-)), so we can credit you with the find! It’s especially helpful if you include a link to the comment you’re nominating… hover over the comment and you’ll see Share and Report options. Click Share, then choose ”copy url” and paste that into your message to us. The visual systems of vertebrates are fundamentally different from those of the visual systems of all other animals. There are two different types of photoreceptor cells, both of which can be found in most organisms that have sight or can detect light. One type are called ciliary photoreceptors, because the molecules that absorb the light are on cilia (tiny hair-like structures) within the cells. The other type of photoreceptor cell is called rhabdomeric; the light-absorbing molecules are located on rod-like structures within the cell. Further, these two types of cells differ in their chemistry and their mode of transduction. The photoreceptor cells used in the eyes of arthropods (insects, spiders and crustaceans), cephalopods (octopi, squid and cuttlefish), and various worms are primarily rhabdomeric, while in vertebrates, they are ciliary. Why? A new paper (summarized in this report) sheds light on this difference. The early creatures that developed the ability to detect light had three organs for that purpose. They had two eyes (or perhaps more primitive organs) place laterally on either side of the creatures’ face, but there was also a light detecting organ placed generally around the top of their heads for the purpose of tracking circadian rhythms (i. e. is it night or day?). In these early creatures, the photoreceptors in the eyes were rhabdomeric, while the photoreceptors in the organ on top of the head had ciliary photoreceptor cells. Early chordates had the same sort of visual system, that is eyes with rhabdomeric photoreceptors, and the circadian organ with ciliary photoreceptors, but one of these creatures underwent a change in its mode of life, becoming stationary, and probably burrowing. Under these conditions, it no longer needed sight, so, over millennia, it lost its rhabdomeric eyes, though it retained its circadian organ, as it still needed a sense of what to do at various times of the day. Eventually, that circadian organ ultimately developed sight, and when the descendants of this creature changed its mode of life again to one that required sight, that single eye. Possibly within a few million years, this animal changed its lifestyle again. A return to swimming reintroduced the need to control steering and measure its own body motion for efficient filter-feeding (sifting food out of water) and avoiding predators. This pushed evolution to develop the midline eye by forming small eye cups on each side. These eye cups later separated from the midline eye, moved out to the sides of the head and formed new paired eyes: our eyes. The loss and regain of vision happened between 600 and 540 million years ago. Components of the midline eye remained and became the pineal organ in the brain, which produces and releases the sleep hormone melatonin. So the new eyes evolved from that midline eye that used ciliary photoreceptors, unlike the sighted invertebrates, and all vertebrates, being descended from this early chordate, have eyes with ciliary photoreceptors. And the pineal gland is still telling us what time of the day it is. On to the Comments: From A Pagan in Arizona: Two nominations: A comment from Damon Griffin on a diary by mikeymikey from the Friends of Gaia group, discussing a “Buynott”. In which he talks about corporate greed, the evil of oligarchy, and the impact of individuals efforts to combat it. 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