A swimming eyeball?

Here’s one of the weirder things I’ve come across in biology. When lamp shells are just tiny 36-hour-old embryos–just a clump of a few hundred cells–they can see. Many cells on their outer surface express a photoreceptor gene, and they show evidence of being able to swim towards light. In other words, these lamp shells are swimming eyeballs.

Aside from the surrealism, this discovery is also cool because it might be a model for how our own eyes evolved. Perhaps they started out in a similar way. For more details, check out my story in today’s New York Times.

[Image: Coreldraw]

7 thoughts on “A swimming eyeball?

  1. Nice article. I hope this prompts Todd Oakley to start blogging again, I used to be a big fan of Evolutionary Novelties.

  2. Really interesting article.

    But I’m confused by a few things:

    1. in the article, Dr. Oakley is cautious:

    But he cautioned that just because the photoreceptor gene was active in the early embryo, that did not necessarily mean that the lamp shells were able to see. “Other possible photoreceptive mechanisms should also be ruled out,” Dr. Oakley said. “Correlation does not mean causation.”

    What would qualify as “seeing?”. What type of organism response?

    2. (probably related the last question) What qualifies as an “eye”? is it image formation? Behaviorally directed response to light? Or any form of response to light (as in the ‘pineal eye’)?

  3. John–

    1. Bacteria can respond to light, but they don’t use opsins (the photoreceptors in our eyes). So it’s possible opsins were serving some unknown function for the lamp shells, while some other set of proteins was sensing light.

    Seeing would mean extracting information from light using opsin photoreceptors.

    2. There are eyes that form images, and eyes that detect light direction. Since they are homologous, it’s fair to call them eyes.

  4. Seeing and Looking are different and are at distinctly different levels of cognition.

    A cow sees the full moon. A 5 year child looks at the full moon.

    Looking implies that the individual images formed by the individual light receptors are:
    a: continuously integrated into a single dynamic images,
    b: holistic implications (to the “self”) of the changing integrated images are assessed and
    c: appropriate (at & for that time) responsive motor actions are executed.

    Vasanth

  5. Vasanth BR — Seems to me that cows do precisely abc when looking at the full moon. Its just the response is different than the 5 year old child staying up past her bedtime.

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