We read with great interest the article by Brodsky1 on the evolution of human stereopsis. Brodsky shows that the oblique muscles in humans seem to have abandoned their previous role in lower organisms in promoting panoramic vision and instead serve to stabilize the eyes to facilitate stereopsis. As Brodsky points out, this may be a very concrete example of evolutionary exaptation. This controversial term was originally coined by Gould and Vrba2 and means that a certain gene or trait that has evolved to fulfill a specific function takes on a new role (ex) and gets a new function (aptus) for which it was not originally designed.
Zetterberg H, Zetterberg M. Evolution, Exaptation, and Stereopsis. Arch Ophthalmol. 2005;123(9):1281. doi:10.1001/archopht.123.9.1281-a