Pub. date: 2010 | Online Pub. Date: December 16, 2009 | DOI: 10.4135/9781412972000 | Print ISBN: 9781412940818 | Online ISBN: 9781412972000| Publisher:SAGE Publications, Inc.About this encyclopedia
Visual System: Evolution of
Visual systems include light-detecting cells (photoreceptors), typically eyes as organs with image forming capacity, and neuron networks that extract useful information from the patterns of light that activate the photoreceptors. This information is used in numerous ways, guiding daily and annual cycles of activity, mating, migration, and other behaviors, as well as motor actions that preserve life and lead to successful reproduction. Eyes have proven to be so useful that they have evolved at least twice and probably many times. They vary in many ways, while consistently providing information about wavelength and intensity of light and sharing molecular mechanisms of photo detection. Thus, some of the same genes are used in the development of independently evolved photoreceptors and eyes. Even though light detection does not depend on having eyes, eyes are structures that protect receptors from damage when focusing or channeling light so that at least a crude image of ...