The third eye is not just a metaphysical yoga concept.
Scientists have discovered the origin of the strange central cornea buried deep in our skull, our earliest ancestor about 600 million years ago. This tri-cornea theory was detailed in an eye-opening study published in the journal Current Biology.
The team set out to illuminate the pineal gland, a pea-sized organ inside the human skull that explains how our body reacts to light in the dark, even though it has long been cut off from sunlight.
Found in almost all vertebrates, from cats to frogs and humans, this superior light receptor produces melatonin, a hormone that regulates sleep and wakefulness.
Although written about by doctors since ancient times, the origin of the “mind’s eye” was unclear – until now.
Study author Prof Thomas Baden, a neuroscientist at the University of Sussex and a co-author, said they wanted to find “the original solution to vision,” and the degree to which “species simply copied or modified it to make it their own.”
“What exactly are patterns?” he wondered, according to the BBC’s Science Focus Magazine. “As you do this over time, you start to wonder, what is the first eye?”
To gain insight into the evolution of our optic organ, the team looked back to our earliest ancestors – a tiny, sea-dwelling worm from 575 million years ago.
This critter sported two side eyes for navigation and a third lens on top of its noggin for monitoring light levels and staying upright.
This design continued until about half a billion years ago, when they started digging in the dirt, meaning they no longer needed their side eyes to walk.
Accordingly, our underground ancestors abandoned their peripheral characters to conserve resources, effectively leaving them with a third receptor that allowed them to distinguish from the ground and day from night.
This cyclops-like configuration separated vertebrates from other classes, which retained their lateral retinas.
What should we answer with the forward-looking lenses we have today? Eventually, some ancestors left the subsurface and returned to the sea as filter feeders, necessitating tools for navigation – in other words, we needed our eyes back.
Left with no other option, parts of the third eye developed and migrated to the sides of the head, eventually developing into retinas. However, the third eye remained an evolutionary straggler.
In doing so, they proved that both our retinas and the pineal gland evolved from an ancient organ and are not separate as some experts have claimed.
Coincidentally, this study did not need to examine the eyes to shed light on our ocular evolution. They simply reviewed existing study data and genetics from animals such as fish and lampreys to determine how the organ of vision works in our relatives.
Coincidentally, not all critters’ third eyes are hidden from view.
The tuatara – a strange, lizard-like creature from New Zealand – has a large central orb that appears at the top of its head like a hybrid monster from Greek mythology.
Similar to humans, this eye is not used to see, but to detect changes between light and dark and use this information to control its circadian clock.
