CSB #5: Swimming Eyeballs

Brachiopods, or "lamp shells," are, in effect, marine worms that live in shells. A long-standing scientific question has been whether or not they can see; recently, it seemed as though some dark spots on the larvae were light sensors. Under closer examination, it was revealed that they were primitive "eyes," or the model of eye that is a "swimming eyeball." Basically, this means that it could sense light or dark, but could not do much beyond that.

Above: brachiopods

This is the first step towards the evolution of an organ as complex as the eye. Darwin himself did not feel as though something like the eye, which is, at first glance, perfect, could be explained by his ground-breaking theory of evolution. However, he did come up with steps in the evolution of such an organ, and his theory had the backing of real, living organisms with that kind of eye. This is the really phenomenal part of the theory: there is incontestable

evidence for large parts of it. The first step of his theory in the evolution of the eye, though, was unsupported until the work with the brachiopods.

Scientists also checked to see if the photoreceptor, or light receiving, genes were active at any other stage of development. Surprisingly, more of the undeveloped embryos moved towards a light source than expected, the expected being that none would move. At this point, the brachiopod embryos have no brains, no eye-like organ, or anything.

Right: eye spots on brachiopod larva

It was absolutely fascinating that our eyes, such intricate, elaborate organs, could have started out as nothing more than a bunch of photoreceptor cells. Aside from this, the fact that the undeveloped embryos could sense light is truly unexpected. Scientists hypothesize that the yolk blocks light from some directions, and this allows the brachiopod-to-be to sense the light. How this would work is not exactly clear to me, especially if it has no neurons at all and can react to its environment. Not only can it sense the light, the embryo also moves towards it.

In regards to Darwin's theory of evolution, it seems even more fantastic because proof is still being sought for it, one of the most controversial theories. The new discoveries made today, confirming his ideas, show how truly ahead of his time he was and in what accurate detail he surmised about the development.

Resources:

Article:

Zimmer, Carl. "In a Marine Worm's Eyes, the Theory of Evolution." The New York
Times. N.p., 1 Mar. 2011. Web. 6 Mar. 2011. .

Picture:

http://www.treasuresofthesea.org.nz/uploads/images/147_image_main.jpg (brachiopod)

https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEicyQ-gEozz_kvpVA6eIALX9_2ZGl6BMLwc1tvk2oj-ocTyXcHNNh9grpOtxnIFCd5Ke796tJqaHg431nhIDH9Gd_nroOFULRlQtDDA1TCdjImGIwGGX2BXaNh15NN-ThOCyPneW_LtsMw/s200/
BrachiopodLarva.jpg (larva)