Charles Darwin acknowledged right in the beginning that the eye would be a difficult case for his new theory of eye evolution to explain.
Before he made his statement about the evolution of the eye, he stated that it seems highly absurd that the eye could have evolved.
Nevertheless, he and scientists after him studied the eye in order to give the answers we have today.
Many skeptics of Darwin’s theory argue that it is impossible. Such a complex mechanism like the human eye can’t develope through random mutations and natural selection.
The critics ask how evolution if it occurs gradually, could have created the separate parts of the eye – the lens, the retina, the pupil and so forth – since none of these structures by themselves would make vision possible.
And yet, as early as 500 million years ago, the evolution of the eye started.
According to scientists, the first eye-like structure was a simple light spot, such as the one found in single-celled organisms like euglena.
This eyespot is sensitive to light – when it detects the light, the euglena travels in the direction of the light source to photosynthesis.
People consider that this is the simplest precursor of the eyes we have today.
A more complex structure, which can be seen as the next step in the evolution, is the eye of the planarian flatworm.
The planarian eye is cupped rather than flat – this shape enables it to better sense the direction of the incoming light.
More information is provided because it can now see shadows.
This ability allows an organism to hide from predators.
Over time, the deeper the light cups grew in some organisms, the smaller the opening at the front became.
This resulted in a pinhole effect. Pinhole eyes can be found in the nautilus, an ancestor of the octopus, and it is the highest revolution one can have without a cornea or lens.
Exactly the appearance of the lens is the key step towards the kind of eye we know.
Before lens, through a thin layer of coating over the pinhole was developed, now called the cornea.
The cornea protects the eye from infection, allowing the inside of it to fill with fluid that improves light sensitivity and processing.
The lens was created by crystalline proteins formed at the surface.
Thanks to the lens, the eye can change its curvature to adapt to near and far vision.
This way, beginning with a simple light-sensitive spot, the eyes evolved to the complex organ they are now.
Let’s find out what makes our eyes even more amazing! Here are some facts you may not know:
The eyes are a remarkable mechanism that enables us and other animals to understand the world around us better.
Thanks to these small but vital organs, we have survived years of danger and evolved to become the people we are today.
Our ability to see the world in color and detail makes our lives so much brighter and happier and we should appreciate it – after all, it goes by as fast as a blink of an eye!
Author: Iliana Stoyanova