The human eye is a sensitive, complex organ that researchers have studied for thousands of years, and it’s still no less awe-inspiring. Those gelatinous spheres that let us binge-watch ASMR videos till we knock out may also be a lingering remnant of an ancient ancestor.
According to a theory published earlier this year in Current Biology based on work by researchers from Lund University and the University of Sussex, our sophisticated eyes may have evolved from a single light-sensitive eye sitting in the middle of a tiny worm-like creature’s head roughly 600 million years ago that, according to an official artist rendering, looks like an abyssal beast you’d fight in a D&D campaign.
It’s a sedentary little guy that researchers believed once had a pair of light-sensitive organs that were something like eyes. It gradually lost them after it decided to veer its evolutionary path toward just kind of chillin’, hangin’ out, filterin’ plankton from seawater. So, these two ocular organs that pared down to one eye that could tell the difference between light and dark and allowed it to have a sense of direction… and that’s about it.
The Tiny Cyclops’ Eye Might Explain a Difference Between Humans and Squids
Maybe the species was just in a depressed funk for millions of years, but eventually it got out of it and, with a renewed sense of purpose in life, decided to start being active swimmers again. So, evolution ramped back up and started slowly separating that single eye back into two. The median eye was repurposed into the paired retinas found in vertebrates today. That, the researchers argue, might explain why vertebrate eyes develop from brain tissue while insects and squids build their eyes from tissues near the skin.
But the researchers’ theory suggests that the original median eye never completely disappeared. It might have survived to this day as the pineal gland, the part in the brain that produces melatonin and helps regulate our sleep-wake cycle.
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