[astrobe_]

I wouldn't call that a side effect, because it is most likely a must-have feature and plants were selectively pressured on that (although I know some plants or trees have red to dark red leaves).

But yes. Logically, things have a natural color. Then animals progressively acquired the ability to distinguish colors because it was advantageous - for instance to spot a naturally brown yummy insect on a naturally green leaf.

From there, one can imagine an amplification or reinforcement process induced by co-evolution: plants take advantage of the fact that animals can see colors, animals take advantage of the fact that healthy plant produce fruits of a specific color. It eventually turned into an armed race at times: TFA opens with the example of a blue belly lizard, but one cannot help but think about chameleons.

It was probably unavoidable as soon as something like a photo-sensitive cell appeared. And it is also probably the same thing with perceptions that are less obvious to us, such as odors, sounds, or vibrations (other than of air or water - although I wouldn't be surprised if hearing evolved from that point).

[timewizard]

> it is most likely a must-have feature

Why? I can imagine other chemical compounds with different colors that perform the same function just with a greatly reduced efficiency.

If there isn't any evolutionary competition then there could have been a long period of time before plants with chlorophyll started being produced and then dominating the landscape.

[astrobe_]

Yes, organisms don't have to be optimal in everything - for instance the peacock's tail is probably a bit detrimental for various things other than signaling.

When there's no environmental pressure, genetics can do whatever it wants (to a certain extent), which leads to a diversification which in turn is very valuable when a constrain suddenly appears in the environment, or to conquer new biomes. This remembered me of the "Cambrian explosion" [1] and coincidentally this article refers to the evolution of the eye.

With regard to green chlorophyll, it is safe to say that a very common environmental pressure is present that makes it green, judging from how dominant it is. I guess that it doesn't apply to species that have red/dark red/purple foliage due to their specific ecosystem niche, or maybe an even greater constrain is at play ?

[1] https://en.wikipedia.org/wiki/Cambrian_explosion

[kevin_thibedeau]

Animals with camouflage coloration don't need to be able to see that color themselves. They can find each other with chemical signals and sound while hiding from their predators.