Another significant difference is that fish went on to evolve color vision by increasing the variety of light-sensitive proteins in their eyes; coleoids never did and are probably color-blind. I say “probably” because the idea of color blindness in such colorful animals has flummoxed generations of scientists, and a few have suggested that modern squid and octopuses have the potential to exhibit unconventional kinds of color vision. Perhaps light-sensitive pigments distributed throughout their bodies could send color signals back to the brain.9 Or maybe, by quickly changing the shape of their
...more
