Your eyes are half a billion years old

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Look after your eyes – they are at least half a billion years old, and a good deal older than your brain. The eyes are one of our most remarkable and precious organs, yet their origins have been shrouded in mystery until quite recently, explains Professor Trevor Lamb of The Vision Centre and Australian National University, who has devoted more than 30 years to investigating their secrets.


Prof. Lamb has just published a major scientific review of the origin of the vertebrate eye and vision, summarising the findings of hundreds of scientists round the world.

"There are profound questions about the eye which are still not easy to answer because it appeared so very long ago," he says. "Why did the eye develop? Why are there many different kinds of eye, including one for insects and crustaceans – and one for vertebrates like us?

"What kinds of animals needed these incredible seeing machines and how did they use them? How deep into time do the roots of vision go? How has the eye influenced our subsequent development?"

The deep origins of 'sight' go back more than 700 million years when the earth was inhabited only by single-celled amoeba-like animals, algae, corals and bacteria. At this time the first light-sensitive chemicals, known as opsins, made their appearance and were used in rudimentary ways by some organisms to sense day from night.

Ancient cells already had signalling cascades that sensed chemicals in their environment, and the advent of opsins allowed them to sense light. "But these animals were tiny, and had no nervous system to process signals from their light sensors," he explains.

Over the following 200 million years those simple light-sensitive cells and their opsins slowly and progressively became better at detecting light – they became more sensitive, faster, and more reliable – until around 500 million years ago they already closely resembled the cone cells of our present day eyes.

"The first true eyes, consisting of clumps of light-sensing cells, only start to show up in the Cambrian, about 500 million years ago – and represent a huge leap in the evolutionary arms race," Prof. Lamb says. "Creatures that could see clearly had the jump on those that couldn't.
 

Written By: Medical Xpress
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  1. Can someone quickly explain how they can tell what type of eyes 500 million year old organisms had. As in the working of the eye and how well it may have worked. Are the fossils that well preserved? Do they compare the fossils to similar organisms alive today? Forgive my ignorance.

    • I believe your intuition is leading you correctly.

      We see patterns in the fossil record that are echoed in molecular data and then organisms surviving to this day (whose first ancestors appear in specific chronology in the fossil record) that have photosensitive patches, then eye spots, then eye spots with ganglia behind them then then then then …. We reconstruct the past with the remnants of the past, the genetic code, and the examples from the present, along with a bit of creativity, logic, reason, experiment, and as you have clearly demonstrated, intuition.

      While the eye develops in chronological sequence, so does tons of other stuff… stuff that is kind of specialized, like colonial organisms vs multicellularity, prokaryotes to eukaryotes, # of embryonic tissue layers, proto vs. deuterostome, one way vs blind digestive cavities, head tail and dorsal ventral determination, patterns of embryo cleavage, segmentation, even things like the number of chambers in a heart.

      There are so many patterns that all overlap and point towards Darwin’s realization, that, once examined and digested, the idea colors almost everything you see… Almost.

      In reply to #1 by Givens:

      Can someone quickly explain how they can tell what type of eyes 500 million year old organisms had. As in the working of the eye and how well it may have worked. Are the fossils that well preserved? Do they compare the fossils to similar organisms alive today? Forgive my ignorance.

        • In reply to #5 by Sample:

          In reply to #3 by crookedshoes:

          So what came first, the eye or the brain? Perhaps that’s a rudimentary way to look at it, no pun intended.

          Light sensitivity is a widespread feature of many living organisms, with chloroplasts (descended from independently living cyanobacteria) in plants photosynthesising, and some plants having the capability to move or grow towards sunlight.

          Light sensitive cells and nerve cells evolved together in animals, so light detection was incorporated in the development of brains from rudimentary beginnings.

          While vertebrate eyes are being discussed here, modern Molluscs have a range of eyes from basic light sensitive patches, to the complex eyes of the octopus. http://molluscs.at/mollusca/index.html?/mollusca/eyes.html, which illustrate the stages of evolution.

          Mollusc eyes are independently evolved (as are insect eyes) with no connection to vertebrate eyes.

    • In reply to #4 by SGde3a:

      Interesting to note that the eye also de-evolves under dark cave-like conditions.

      The “grotto sculpin” (not officially designated as a separate species) is believed to inhabit a specific area. Come September, the USFWS will vote yay or nay putting the sculpin on the ‘endangered species list’.

      Poor little things – it seems most folk don’t appreciate how vulnerable and valuable cave/karst systems are.
      One cave tour I took, the guide turned off the lights – the complete darkness is a shock!

      • That complete darkness takes my breath away (quite literally)!

        In reply to #10 by bluebird:

        In reply to #4 by SGde3a:

        Interesting to note that the eye also de-evolves under dark cave-like conditions.

        The “grotto sculpin” (not officially designated as a separate species) is believed to inhabit a specific area. Come September, the USFWS will vote yay or nay putting the sculpin on the ‘end…

    • The genes for making the eye do not “de-evolve”. A control gene called a hox gene shuts off. Then, the eye is not made. Making an eye is extremely energetically expensive and in complete darkness it is an expenditure that causes makers of eyes to be out competed (food is often scarce in cave systems as well). So, for the organism that has the beneficial mistake of the eye hox gene being shut off — it is actually an advantage! So, yet again, evolution!

      In reply to #4 by SGde3a:

      Interesting to note that the eye also de-evolves under dark cave-like conditions.

    • In reply to #9 by SaganTheCat:

      my favorite question-to-stump-a-darwinist is “so which evolved first? the eye or the eyebrow?”

      sadly very few trilobite eyebrows have been preserved. such a shame

      I take it that eyebrows serve to prevent sweat from running into the eyes. So in land animals, the eyes would have come first, I should think. When women used to pluck their eyebrows, did they suffer in hot weather?

  2. There’s recently been a post-Cambrian explosion in vision evolution. Though non-biological, in that it is the product of technology artefacts like CCD associated with human intelligence and scientific advances.

    We are now living in an era where every 2nd human, and even some of his dogs, carries a high res video camera that includes the ability to upload gps tagged data via extensive mobile telecoms networks to make these images available to any other human or semi-human intelligent organism capable of accessing Google.

    And that’s without even mentioning the capability of this technology to exceed the normal range of optical spectrum, or even the temporal frame. As can be done for adjusting the rate of time flow and performing pixel analysis and modification to highlight minute high or low frequency changes in colour variation or movement that otherwise would be undetectable owing to being outside the normal scope of human experience and awareness. Plus it’s also interesting that the underlying manufacturing processes for these tech gadgets critically depends on photographic techniques that mimic the mechanisms of biological optics.

    It’s not all positive though. There’s been a huge setback for the search for extra-terrestrial intelligence and cryptozoological specimens, not to mention vatican-credible miracles, owing to the sudden collapse in the rate of accumulating evidence, apparently in inverse proportion to the growth in availability of smartphones. According to xkcd.

    • In reply to #13 by Pete H:

      There’s recently been a post-Cambrian explosion in vision evolution. Though non-biological, in that it is the product of technology artefacts like CCD associated with human intelligence and scientific advances.

      So not evolution then.

      It’s important not to confuse people when communicating, using words with appropriate meanings is the number one place to start. Using the wrong words is worse than remaining silent as it also confuses. Evolution is a word so poorly understood that it should never be deliberately misused by someone that knows better.

      I was disappointed enough in Comment 4 but crookedshoes managed to cover that before me, this is just off topic completely…

      We are now living in an era where every 2nd human, and even some of his dogs, carries a…

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