When Life received an upgrade

In the beginning those rare lifeforms not stationary, meandered blindly over the slime, grazing on microbial life. Then ‘suddenly’, 542 million years ago, an evolutionary storm upended this quiet world.

In the rapid burst of evolution known as the ‘Cambrian explosion’, the first complex eyes evolved.
A new stimuli! Fresh information about the world became available. Photoreceptor proteins in cells were able to absorb the ‘visible’ electromagnetic radiation. This triggered changes in the cell’s membrane potential, providing Information about the wavelength and intensity of a ‘light’ source.

By reducing the size of the opening, organisms achieved true imaging, allowing for fine directional sensing and even some shape-sensing. Eyes of this nature are currently found in the nautilus.
Lacking a cornea or lens, they provide poor resolution and dim imaging, but are still, for the purpose of vision, a major improvement over the earlier rudimentary light sensors.

Each creature accesses the sensory information it is ‘hard-wired’ to receive, with eyes showing a wide range of adaptations to meet the requirements of the organisms which bear them. Eyes vary in their visual acuity, the range of wavelengths they can detect, their sensitivity in low light, their ability to detect motion or to resolve objects, and whether they can discriminate colours.

‘Vision’ is not only to be found in the eyes. From the point of view of biological evolution the pineal gland can be seen as a kind of atrophied photoreceptor in mammals. In non-mammalian vertebrates it still retains its photoreceptive qualities. In the epithalamus of some species of amphibians and reptiles, it is linked to a vestigial organ, known as the ‘parietal eye’ which is also known as the ‘third eye’. It is sensitive to changes in light and dark, but it does not form images, having only a rudimentary retina and lens.