It occurred to me that the visual capabilities of predators are relavent.
Dogs don't see in color; do any mammalian carnivores other than primates?
I think I heard that hawks see in color. In any case, not all carnivores
do see in color, which perhaps says something about the value of color
vision for hunting animal prey.
Why do we have color vision? Maybe because it helps us tell whether fruits
are ripe and good to eat? We passed through a fruit-eating stage as primates.
I have a theory that color vision was one of the things that led us to
evolve increased intelligence. The idea is, that color vision increases the
amount of information taken in by the eyes. This creates an increased
value for brain organizations that can utilize the increased amount of