Maybe this would not be proper question on physics stack exchange, but it originated from physics book so I'll post it here anyway. I have much interest in color recognition evolution. I'm studying the famous Jackson E&M book, and it has a following sentence; (on p.314 of 3rd Ed.)

'the reader may meditate on the fundamental question of biological evolution on this water-soaked planet, of why animal eyes see the spectrum from red to violet and of why the grass is green.', with the graph of absorption coefficient for liquid water vs. freq.

The graph is same as the following. https://www.britannica.com/science/absorption-coefficient

I can see that animals have evolved in the way to exploit the water-transparent frequency, but I'm not sure how that relates to the color recognition. So the human evolved to see grass as green, and use colors from red to violet (using RGB cones). Color itself is invention of animals, nothing inherent in nature. But why it had to be that way? In my first thought, human could have different cone cells, and could feel grass as blue, could used different primary colors. (I cannot imagine that because my world is RGB world but I think thats possible)

Jackson seems to imply that there is a reason that it has to be this way, but I'm cannot see the reasoning. Maybe was he just suggesting to think?

  • $\begingroup$ The quote you provided doesn't seem to imply anything about color recognition. "Why the grass is green" refers to the fact that chlorophyll in grass (and other plants) evolved to preferentially absorb red and violet light. It's a statement about the absorption spectrum of a particular molecule, independent of whether certain animals see it as being green. $\endgroup$ Commented Jun 3, 2018 at 23:13
  • $\begingroup$ @probably_someone I'm sorry, then why did plants evolve to absorb red and violet light? $\endgroup$
    – Septacle
    Commented Jun 3, 2018 at 23:15
  • $\begingroup$ Well, that's a different question entirely. This site seems to answer it: scienceline.ucsb.edu/getkey.php?key=500. Basically, it's because absorbing too much energy would kill the plant, so the absorption spectrum needs to be somewhat far away from the peak of the Sun's emission spectrum (which is in the vicinity of green light). $\endgroup$ Commented Jun 3, 2018 at 23:18
  • $\begingroup$ As far as "why animals see the spectrum from red to violet," first of all, not all animals do (bees can see into the ultraviolet, and mantis shrimp have a ridiculous amount of spectral range), and second, because that's where most of the Sun's light is emitted (after being filtered by the atmosphere). $\endgroup$ Commented Jun 3, 2018 at 23:21
  • $\begingroup$ And many animals don’t have color vision, only black and white... Hence why hot pink camo works for deer hunting. $\endgroup$
    – Jon Custer
    Commented Jun 3, 2018 at 23:24


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