Short answers, pulled from the story.
The first proto-eyes evolved among animals approximately 540 million years ago during the Cambrian explosion. This event marked a pivotal moment in the history of life on Earth when the common ancestor of all animals possessed the biochemical toolkit necessary for vision.
The PAX6 gene is a key factor in eye development that is shared across all modern eyes. This genetic blueprint suggests a single common origin for all visual systems and allowed for the development of complex optical systems in vertebrates, cephalopods, and arthropods.
Scallop eyes use layers of guanine crystals to bounce light onto a central point through mirror-based reflector systems. This mechanism differs from the lens-based systems found in humans and other mammals where the lens focuses light onto the retina.
The mantis shrimp possesses the world's most complex color vision system capable of detecting hyperspectral color and polarized light. This crustacean can detect a wide range of colors including ultraviolet light which is invisible to humans.
Pit vipers have developed pits that function as eyes by sensing thermal infra-red radiation in addition to their optical wavelength eyes. This adaptation allows them to detect the heat signatures of their prey even in complete darkness.
The most sensitive pigment rhodopsin has a peak response at 500 nanometers. Small changes to the genes coding for this protein can tweak the peak response by a few nanometers to adapt to specific environments.