Evolution of Eyes: Adaptation, Performance, and Diversification in Animal Phyla

1. Eyes evolved dozens of times, using the same molecular building blocks in a wide variety of designs. How do observed structural features contribute to survival? How are functional requirements (resolution, field coverage, sensitivity) met? How is a critter’s particular eye adapted to the critter’s lifestyle? How closely does an eye approach physical limits in performance? (e.g. Diffraction, photon catching)? How might a given eye be improved (at no cost?) by refinement or by radical redesign?

2. Most animal phyla originated in a relatively brief span of geological time • The fossil record and molecular studies concur that the diversification that produced most animal phyla occurred rapidly on the vast scale of geologic time. • This lasted about 40 million years (about 565 to 525 million years ago) during the late Precambrian and early Cambrian.

5. Diffraction of light waves limits resolution: Angular resolution = l/D radians Worse for small lens diameter Requires large lens diameter …large facets in compound eye

6. Diffraction at large & small pupils

7. For good resolution over a large field, the compound eye needs many large facets, leading to an eye hundreds of feet across:

8. The chamber or camera eye (a) and the superposition eye (c) collect more light from each visual direction than does the apposition compound eye (b)

9. Mantis shrimp eyes, showing midband array of ommatidia