One of a series of articles - first published as notes on FaceBook.
It took a long time in the history of life's evolution before the eye was invented - in fact scientists believe that there have been many different attempts - different varieties of eye.
"Complex eyes appear to have first evolved within a few million years, in the rapid burst of evolution known as the Cambrian explosion.
There is no evidence of eyes before the Cambrian, but a wide range of diversity is evident in the Middle Cambrian Burgess shale, and the slightly older Emu Bay Shale.
Eyes show a wide range of adaptations to meet the requirements of the organisms which bear them.
Eyes may vary in their acuity, the range of wavelengths they can detect, their sensitivity in low light levels, their ability to detect motion or resolve objects, and whether they can discriminate colours."
"Whether one considers the eye to have evolved once or multiple times depends somewhat on the definition of an eye.
Much of the genetic machinery employed in eye development is common to all eyed organisms, which may suggest that their ancestor utilized some form of light-sensitive machinery – even if it lacked a dedicated optical organ.
However, even photoreceptor cells may have evolved more than once from molecularly similar chemoreceptors, and photosensitive cells probably existed long before the Cambrian explosion.
Higher-level similarities – such as the use of the protein crystalin in the independently derived cephalopod and vertebrate lenses – reflect the co-option of a protein from a more fundamental role to a new function within the eye.
Shared traits common to all light-sensitive organs include the family of photo-receptive proteins called opsins.
All seven sub-families of opsin were already present in the last common ancestor of animals.
In addition, the genetic toolkit for positioning eyes is common to all animals: the PAX6 gene controls where the eye develops in organisms ranging from mice to humans to fruit flies.
These high-level genes are, by implication, much older than many of the structures that they are today seen to control; they must originally have served a different purpose, before being co-opted for a new role in eye development.
Sensory organs probably evolved before the brain did—there is no need for an information-processing organ (brain) before there is information to process."
Text courtesy - wikipedia
An interesting extract from the above Wiki link is this.
"It is likely that a key reason eyes specialize in detecting a specific, narrow range of wavelengths on the electromagnetic spectrum—the visible spectrum—is because the earliest species to develop photosensitivity were aquatic, and only two specific wavelength ranges of electromagnetic radiation, blue and green visible light, can travel through water. This same light-filtering property of water also influenced the photosensitivity of plants."
(Transmission of light through air does not appreciably change its spectral composition, but transmitting light through water, even through the clearest water, does, and this can change the resulting colour appearance beyond recognition. In clearest water, long wavelength or red light is lost first, being absorbed at relatively shallow depths. Orange is filtered out next, followed by yellow, green, and then blue.)
Early life forms, although somehow aware of Electromagnetic Radiation (EMR) as a source of energy - therefore could not "see it" - as we have come to interpret seeing. Plants required & presumably evolved in response to this EMR as a "food source" - an energy source. Parallel to this I will mention that astronomy learns much about the stars from pictures derived from processing EMR in the long wave end of the EMR spectrum - radio waves.
Picture courtesy - chemwiki
In this process a computer will perform a similar function to our brain - in decoding EMR data and constructing a picture.
So let's recap - our eyes are attuned to an extremely narrow band within the known spectrum of EMR (which we have appropriately named visible light) - but which imposes limits to what we can actually "see."
"It is impossible to "see" anything smaller than the wavelength of the light you are using.
So to study atoms or molecules, you must use light waves about their size or smaller.
The ALS produces light with wavelengths about the sizes of atoms, molecules, chemical bonds, and the distances between atomic planes in crystals."
We cannot naturally see emissions or reflections of EMR outside of the narrow band of visible light - but they most certainly exist. An analogy here would be a person with a hearing range of only one octave - no frequencies outside of that octave, lower or higher notes, could be detected - sitting in a concert hall listening to a symphony.
It is not so much of a coincidence that our eyes have been designed by nature to detect this narrow range of EMR.
"Most of the energy coming from the sun is in the visible region of the electromagnetic spectrum, making up what we call sunlight (white light)."
"The sun provides a broad range of energy, primarily concentrated around the visible and infrared regions.
This energy is an important feature of the background conditions that led to the evolution of our life forms on Earth, and continue to support this life.
There is a small amount of high-energy radiation like x-rays in the sun's energy but these do not penetrate below the topmost layer of the atmosphere, and we do not consider them here."
Text courtesy - telstar
There are instances of totally blind people, learning to "see" by refined audio perception.
"The part of the brain used by people who can "see like a bat" has been identified by researchers in Canada.
Some blind people have learned to echolocate by making clicking noises and listening to the returning echoes.
A study of two such people, published in PLoS ONE, showed a part of the brain usually associated with sight was activated when listening to echoes.
Action for Blind People said further research could improve the way the technique is taught.
Bats and dolphins bounce sound waves off their surroundings and by listening to the echoes can "see" the world around them.
Some blind humans have also trained themselves to do this, allowing them to explore cities, cycle and play sports."
One would imagine in the above scenario - soft, non-reflective objects or surfaces would remain indetectable - or "invisible."
Another example of how the computer/brain processes, but with non EMR data - but the important factor emerging from all of this brief study - is that our environment is perceived, entirely conditional to the sensory equipment used - and is purely the result of familiarisation with the constants and variables of that data - enabling a mental "picture" to be translated from it.
The question I wish to pose is - how convinced are we, that what we see is reality?
Photograph courtesy boingboing.net
We will always have a paper bag over our heads - that is the very design of our senses - our "picture" of reality is entirely a condition of them - they are equally revealing and concealing - yet, understandably, our picture is constructed only from what is revealed.
Could we in our imagination - invent a new sense?
What would it detect - are there other aspects to reality other than the familiarity of light, sound, taste & smell & sensation?
Is it at all possible to even sense the entire spectrum of reality, as it courses through our own being - have we the detection equipment?
Is our own, whole being, in a way, one composite sense - which detects all aspects, simultaneously?
The answer is an assured no.
I am not able to watch TV without a television set.
Any picture we may have of reality is therefore hopelessly incomplete.
Perhaps our most critical sense is the mind's eye - our inner abilty to imagine, to see & understand realities beyond the restricted, yet colourful world suggested by our outer senses.
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