"X-ray Vision" and the Evolution of Forward-Facing Eyes

J Theor Biol. 2008 Oct 21;254(4):756-67. doi: 10.1016/j.jtbi.2008.07.011. Epub 2008 Jul 15.


Why do our eyes face forward, and why do many mammals have eyes facing sideways? Here, we describe results suggesting that the degree of binocular convergence is selected to maximize how much the mammal can see in its environment. Mammals in non-cluttered environments can see the most around them with panoramic, laterally directed eyes. Mammals in cluttered environments, however, can see best when their eyes face forward, for binocularity has the power of "seeing through" clutter out in the world. Evidence across mammals closely fits the predictions of this "X-ray" hypothesis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Evolution*
  • Environment
  • Eye*
  • Face / anatomy & histology*
  • Fixation, Ocular / physiology
  • Humans
  • Species Specificity
  • Vision, Binocular / physiology*
  • Visual Fields / physiology
  • Visual Perception / physiology