Why our eyes are the result of a bizarre evolutionary history

I recently came across a fascinating video about the evolution of the human eye. The information in this article is based on insights and theories from that video, combined with additional scientific context. As I watched, I kept thinking: the more you learn about the human body, the stranger and more impressive it actually becomes.

The idea that we may still carry the remnants of an ancient "third eye" particularly fascinates me. Especially since I've been interested in consciousness, psychedelic experiences, and traditional indigenous peoples for years. During my time with indigenous tribes in the Amazon, the concept of the "third eye" came up regularly. There, ayahuasca is not seen as something ethereal or alternative, but as a normal part of their spiritual and daily life.

Of course, scientists mean something different by a biological "third eye" than the spiritual interpretations one often hears. Nevertheless, I find it remarkable that ancient traditions and modern biology sometimes seem to intersect in unexpected ways.

So I decided to distill the most important insights from the video and elaborate on them below.

Our eyes are actually strangely constructed

The human eye is undoubtedly one of the most complex structures in nature. Almost everything we experience comes through sight. We recognize faces, emotions, colors, movement, and details in a fraction of a second.

But the more scientists look at the human eye, the stranger its design seems to be.

In fact, some animals technically have a "more logical" eye than we do.

An octopus, for example.

That may sound absurd, but when you look at the wiring of the eye, it's actually quite understandable.

And that's precisely where this remarkable evolutionary story begins.

Even Darwin found the eye difficult to explain

Charles Darwin once wrote that the idea of an eye arising entirely through evolution seemed almost absurd.

I understand that.

An eye contains lenses, photoreceptor cells, automatic focus, neural pathways, and real-time image processing. It almost feels like it must have been designed.

Yet modern science shows otherwise.

Eyes did not arise all at once. They developed step by step over enormous timescales.

And what I find perhaps even more interesting: the eye does not seem to have evolved only once.

Scientists now believe that complex eyes may have arisen independently dozens of times in different animal groups.

Nature, as it were, kept experimenting with vision.

How vision probably began

Everything probably started extremely simply.

The first precursors to eyes were likely nothing more than light-sensitive proteins, called opsins. These could only distinguish between light and dark.

That sounds primitive, but for early organisms, it was revolutionary.

Suddenly, an organism could recognize if it was day or night, when it was safer to move, and if danger might be approaching.

Later, small clusters of light-sensitive cells emerged. Not true eyes, but more like light-spots.

Then the structure slowly began to curve inward, allowing organisms to better recognize the direction from which light was coming.

Eventually, something comparable to a pinhole camera emerged. A primitive eye that could form crude images for the first time.

Only later did fluids and eventually lenses come that could focus light.

What I found bizarre to hear is that some evolutionary models suggest this transition may have happened surprisingly quickly.

Why do our eyes resemble cameras?

If you look at the human eye, you see something that strongly resembles a camera.

We have a lens, an iris, and a retina that captures light.

But other animals developed similar systems completely independently of us.

Octopuses, for example, also have camera-like eyes.

This is called convergent evolution. Two totally different evolutionary lines that ultimately develop roughly the same solution.

Only there's a big difference under the hood.

The human eye is actually built backward

This was perhaps the most interesting part of the entire video.

In humans, the light-sensitive cells are deep in the back of the eye. In front of them is a whole layer of nerves and wiring.

Light must therefore first pass through all sorts of cells before it is actually registered.

This also causes our blind spot.

In an octopus, it works exactly the other way around. The light-sensitive cells are directly at the front, so they don't have a blind spot.

From a technical perspective, that seems smarter.

So why are our eyes built so strangely?

According to recent theories, this has everything to do with a bizarre evolutionary history that goes back hundreds of millions of years.

Our ancestors possibly had one central eye

Researchers believe that very early vertebrate ancestors once had a central light-sensitive structure in the middle of their heads.

A kind of single "middle eye."

These animals probably lived mostly passively on the ocean floor. They moved little, filtered food from the water, and did not need complex visual systems.

Their lateral eyes therefore became less important and largely disappeared.

But one thing remained essential: being able to detect light.

Not to see images, but to regulate biological rhythms. To know when it was day or night.

And that's precisely why that central light-sensitive system persisted.

According to some researchers, this ancestor might have most resembled a small worm-like cyclops creature.

Then our current eyes emerged

Later, the climate changed again, and these animals started to move and swim more actively.

This required depth perception. Direction. Navigation.

And this is where it gets really interesting.

According to this hypothesis, our current eyes would have originated from that original central eye.

The structure developed two offshoots that slowly migrated to the sides of the head.

From these eventually arose the two eyes we have today.

In other words: our eyes could actually be evolved versions of one ancient middle eye.

And that would also explain why the wiring of our retina has remained so strange.

Evolution, after all, doesn't start from scratch every time. It works with what already exists.

Do we still have a third eye?

In a way, yes.

Today, we know that structure as the pineal gland.

This small gland is located deep in the center of the brain and plays a huge role in sleep and our day-night rhythm through the production of melatonin.

What I found striking is that this structure is still strongly linked to light.

Darkness increases melatonin. Light decreases it.

And even stranger: in some animals, this third eye literally still exists.

Some reptiles really have a third eye

Certain reptiles, fish, and amphibians have a so-called parietal eye on top of their heads.

That's not a spiritual concept, but a real biological eye.

It contains a lens, light-sensitive structures, and a primitive retina.

It is directly connected to the pineal gland.

In humans, this structure is hidden under the skull, but evolutionarily speaking, we still seem to carry remnants of this system within us.

That doesn't mean humans have a magical third eye.

But it does mean that the idea of a central light-sensitive organ is probably much older and more biological than most people realize.

Sight completely changed life on Earth

Scientists believe that the evolution of complex eyes had a huge impact on life on Earth.

As soon as animals could see better, an evolutionary arms race began.

Predators became better hunters. Prey animals had to become faster, smarter, and more alert.

That could be one of the major reasons why animal life eventually became so complex.

Without sight, the world would probably look totally different.

Evolution is not perfect

What I love about this whole story is that it shows how evolution actually works.

Not perfect. Not neat. Not according to a strict design.

Evolution improvises.

It reuses old structures and builds upon them.

This sometimes leads to strange solutions: a retina that is backward, a blind spot, and a hidden "third eye."

And yet it all works incredibly well.

Despite their strange construction, human eyes still belong to the most powerful visual systems in the animal kingdom.

And perhaps that's precisely what makes it so fascinating.