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From eye spots to eye shine
  1. UC Davis Department of Ophthalmology, 4860 Y Street
  2. Suite 2400, Sacramento, CA 95817, USA

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    In the marginalia of Darwin's On the Origin of Species, the author's spouse wondered if, indeed, an eye could possibly “evolve” since it is so complex. Others, more recently, have asked the same question. Fortunately, similar doubt did not afflict Darwin. A review of the evolutionary evidence reveals ample evidence that eyes can and do evolve. For example, there are creatures that have multiple and very specific eyes, suggesting that eyes are not only rather easy to evolve, but, in some creatures, ocular evolution can be quite rapid.

    The process of organism photoreception probably started shortly after life began on this planet, stimulated by the sun. Ocular evolution responded to the sun's energy by producing phototaxis leading to crude eye spots, then ascending to the complex and elegant ocular structure of certain birds having two foveae and asymmetric lenses for precise focusing. Fantastic adaptations, often beyond imagination, have occurred and are with us today, including irregularly shaped eyes and special photopigments to view ultraviolet, infrared, and bioluminescence. The extension of the interpretation of electromagnetic waves into realms we cannot understand must create a fantastic panoply of colours and stimulations. And, yet, as ophthalmologists, we rarely consider that any visual system is significantly better than or even that different from our own. This is folly for many species have evolved spectacular and stunning adaptations to the visual imperatives of their world.

    The crepuscular aerial drama of a swallow on the wing hunting for a small erratic insect illustrates the profoundly complex visual processing necessary to provide identification, tracking, pursuit, and eventual capture in a dimly lit and almost clueless three dimensional environment. Yet, a swallow does this hundreds of times a day. Similarly, a bathypelagic piscine predator, living at a depth of 1500 metres, must face staggering problems merely identifying …

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