origin of light-sensitivity: sensors are everywhere (The atheist delusion)

by David Turell , Tuesday, September 05, 2017, 21:42 (2634 days ago) @ David Turell

It seems organisms have light-sensing molecules everywhere:

https://cosmosmagazine.com/biology/seeing-without-eyes-the-unexpected-world-of-nonvisua...

"But scientists have discovered in recent decades that many animals – including human beings – do have specialized light-detecting molecules in unexpected places, outside of the eyes. These “extraocular photoreceptors” are usually found in the central nervous system or in the skin, but also frequently in internal organs. What are light-sensing molecules doing in places beyond the eyes?

"All the visual cells identified in animals detect light using a single family of proteins, called the opsins. These proteins grab a light-sensitive molecule – derived from vitamin A – that changes its structure when exposed to light. The opsin in turn changes its own shape and turns on signaling pathways in photoreceptor cells that ultimately send a message to the brain that light has been detected.

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"The photoreceptors scientists have found beyond the eyes are most commonly located in the central nervous system. Almost all animals have several types in the brain and often in the nerves as well.

"The skin is where we see most other light receptors, particularly in active color-changing cells or skin organs called chromatophores. These are the black, brown or brightly colored spots sported by many fish, crabs or frogs. They reach their highest development in the cephalopods: octopus, squid and cuttlefish. Animals actively control their color or pattern for several reasons, most often for camouflage (to match the color and pattern of the background) or to produce bright, prominent signals for aggression or attracting a mate.

"Surprisingly, there is a second class of light-sensitive molecules besides the opsins, never used for vision (as far as we know). They show up in some nervous structures, such as the brains or antennae of some insects and even in bird retinas. These are the cryptochromes, well-named because their functions and methods of action are still poorly understood. Cryptochromes were originally discovered in plants, where they control growth and annual reproductive changes.

"Now that we know that these photoreceptors can be found throughout animals’ bodies, what in the world are they actually doing? Obviously, their function depends in part on their location.

"Generally, they regulate light-mediated behavior that exists below the level of consciousness and that doesn’t require having an extremely precise knowledge of a light source’s location in space or time. Typical functions include the timing of daily cycles of alertness, sleep and wake, mood, body temperature and numerous other internal cycles that are synchronized to the changes of day and night.

"Biological clocks that maintain regular physiological cycles – and cause the discomforts of jet lag – nearly always are controlled by these photoreceptors. These detectors are also important for the opening and closing of the eye’s pupil to help adjust to varying light levels. Skin photoreceptors like those in fish or octopus often control color and pattern variations.

"In some animals, they have a quite different, and rather amazing, task – providing magnetoreception, the ability to detect the Earth’s magnetic field. This capacity is based on the cryptochromes, which apparently underlie mechanisms for magnetic orientation in animals as different as birds and cockroaches.

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"Finally, an unexpected recent finding in research led by Solomon Snyder and Dan Berkowitz, also at Johns Hopkins University, found that blood vessels in mice contain melanopsin, the opsin used in retinal nonvisual photoreception. They found that this light-sensitive protein can regulate blood vessels’ contraction and relaxation. Since humans are likely to have the same system, this could partially explain the increase in heart attacks in the morning, which are perhaps associated with blood pressure changes occurring at that time."

Comment: This article suggests that development of light sensitivity and then vision was a major drive of the evolutionary process. From fish to insects to primates helpful vision is primary to advanced functions.