THERE is more than meets the eye, whether it is the current US-Israel war on Iran now or the way we got our eyes. In both, it is not the creation of someone. However, an underlying dialectic is at work that needs to be understood. But this article is not about the ongoing imperialist war.

Charles Darwin said that thinking about the vertebrate eye made him "shudder." The lens, retina, and dense network of neural connections all seemed too complicated to have developed over time. Critics of evolution seized this feeling of unease expressed by Darwin. They claimed that a designer must have created such an organ. Intelligent or otherwise.

Studies in evolutionary biology and neuroscience have cleared many of the things that Darwin couldn't explain more than a hundred years ago. Darwin would have appreciated the alternative narrative offered by recent studies on the eye, particularly the research published in the February issue of Current Biology. It shows that the eyes are a material product of history, not a perfect creation. It has left scars from its troubled past and overcame contradictions through the synthesis that emerged.

DESCENT WITH CHANGE

More than 500 million years ago, the story begins with simple sea creatures. Many early organisms had small patches of light-sensitive cells that enabled them to differentiate between light and dark. It wasn't vision in the way we think of it, but it was still useful. It helped regulate daily cycles and the body to adjust to light.

As some of these organisms became more mobile, new demands arose. To move through water, you needed to be more aware of your surroundings. You had to know not only if it was dark or light, but also where the light was coming from. Gradual changes to the arrangement and shape of light-sensitive cells, such as shallow depressions that could indicate the side from which the light was coming, would have been helpful. One of the ways evolution occurs is by modifying existing parts.

Comparative anatomy and fossil evidence suggest that early vertebrates possessed more than the well-known pair of lateral (on the sides) eyes. In addition to these image-forming eyes, many species had light-sensitive structures on the tops of their heads. These are often now known as median or "third" eyes.

These eyes were not the same as the ones on the sides. The median organs were simpler and usually helped the body sense light and control biological rhythms. The side-facing eyes evolved to make clear pictures. Some reptiles and fish still have these structures in different forms. Over time, the median photoreceptive organ in most vertebrates got smaller and more specialised. In mammals, it exists as the pineal gland,  deep inside the brain and no longer directly reacts to light. Instead, it reacts to signals from the eyes to help regulate sleep-wake cycles.

CONTRADICTION AND SYNTHESIS

The story gets even more interesting at the cellular level. There are two main evolutionary lineages of photoreceptor cells in the animal kingdom: ciliary (structures in the eye that are hair-like and detect light, which we can call as C-receptors) and rhabdomeric (structures that are finger-like extensions of the membrane containing pigments to capture light, which we can call as R-receptors). These two types are different in terms of structure and function. In vertebrates, rods and cones usually have C-receptors that only respond to light in one way. Insects and many other invertebrates have R-receptors, which work differently.

Most animal groups keep these systems separate. Vertebrates, like us, on the other hand, show signs of a more complicated past. Some other light-sensitive cells in the eye, retinal ganglion cells, mediate circadian rhythms and come from the R-receptor lineage. The rods and cones of the retina, on the other hand, come from the C-receptor lineage. Vertebrate vision embodies a stratification of evolutionary histories rather than a straightforward substitution of one system for another; diverse cellular lineages adapted, preserved, and amalgamated into a cohesive functional system. The vertebrate retina is not just a sheet of the same cells; it is a highly ordered, layered structure. Light travels through many layers of neurons before it reaches the photoreceptors. Subsequently, complex circuits process the signals before sending them to the brain, which allows the organism to interpret visual information and respond effectively to its environment.

HISTORY OF THE EYE

Recent studies indicate that this complexity evolved progressively as various cell types were assigned new functions and underwent modifications. It's possible that cells originally used for other processes, such as sensing the inner parts of the body, were changed to process visual information. Thanks to the development of complex circuits, animals were finally able to see patterns, motion, and contrast in addition to light. Because of this, the system is both strong and, to some extent, not perfect. But the vertebrate eye of today works very well. It allows you to quickly process complex scenes, differentiate colours, see motion, and see things in high resolution. Its basic structure has stayed the same for hundreds of millions of years, though some changes have occurred. The features of the vertebrate eyes do not make sense in terms of ideal engineering; they do make sense historically. One well-known example is the blind spot, where the optic nerve leaves the retina, resulting in a small empty area in the field of vision. If an engineer were starting from scratch, they might not want to use this kind of design. Evolution doesn't start from scratch; instead, it modifies existing structures, even if that means making them look strange.

The pineal gland is a light-regulated endocrine organ that is a photoreceptive structure. The endocrine system is our body's "chemical communication network" or "master control system." The adaptation of the pineal gland is not a flaw in the sense of failure. Such adaptations are part of the long evolutionary process.

The eye is not the result of planning or design. It is the result of countless small changes, each of which was shaped by whether or not it helped organisms survive and reproduce in their own environments. When Darwin saw the complexity without fully understanding the origin, he shuddered. We now have the tools to trace that origin—not to a designer's blueprint, but to the material dialectic of environment and organism, of contradiction and synthesis, of quantitative accumulation and qualitative transformation.