The human eye is, very subtly, sensitive to the polarization of light. This is an effect known as Haidinger's brush (see Wikipedia article of this name).
What, if anything, is known or at least intelligently speculated about the evolutionary "grounding" for this effect?
Another way to put this question: Some cephalopods and the mantis shrimp have sight that is sensitive to polarization of light and this sense is clearly begotten by evolutionary forces as it helps these animals detect prey and predators. So, is our subtle ability to perceive polarized light a leftover from a genetic forebear that benefitted from this ability? Or is it simply an artifact of the physics of the eye? The physics of Haidinger's brush is quite different from the topology of retinal cells that confers this ability in cephalopods and others I have read about.
A second question and related is: what is our nearest common genetic forebear that is known to exploit polarization sensitivity of its sight?