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I am currently working on a world with a "human" species. The planet is similar to ours and these "humans" would evolve in a similar environment.

I know that bio-luminescence appears mainly where light is scarce, still, I wonder if I can create bio-luminescent "humans" without this environmental pressure.

In my mind, they would use bio-luminescence mainly for communication and more specifically for attraction. They would develop small spots of bio-luminescence in different places (head / hands / back ...). This bio-luminescence could be used at will and its colors could also be modified slightly (between 575 & 680 nm) according to the sensations expressed.

So my question is:

With a different evolution context from ours, could this characteristic be even scientifically plausible?

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  • $\begingroup$ Welcome to WorldBuilding, B.V.! If you have a moment please take the tour and visit the help center to learn more about the site. You may also find Worldbuilding Meta and The Sandbox (both of which require 5 rep to post on) useful. Have fun! $\endgroup$ – FoxElemental May 30 '18 at 19:27
  • $\begingroup$ It doesn’t seem like a vital part of your question, but it’ll be difficult to make the light organ actually change colors. Luciferases produce very specific wavelengths of light, usually in the yellow/green/blue regions, so to get colors in between you’d have to either pixelate the organ or constantly regulate the mix of different luciferases. $\endgroup$ – Dubukay May 30 '18 at 19:58
  • $\begingroup$ @Dubukay you may be interested in this paper: Luciferases with tunable emissions wavelength ncbi.nlm.nih.gov/m/pubmed/28941028 - Also, chromatophores filled with luminescent fluids rather than with pigments seems plausible to me. $\endgroup$ – Asher May 31 '18 at 22:24
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Yes, totally possible.

Many animals have traits and characteristics that have no practical use other than courtship displays. Think of the tails of peacocks, or the singing of frogs and crickets. In many cases, such displays cause those animals to be more vulnerable to predation, since a predator might find their prey more easily if they are being flashy or loud. Some people think that, by making such displays, those animals are showing to their potential mates that they are good enough in surviving that they can afford what would otherwise be, at best, a waste of energy.

I would even go as far as suggesting that this happens in humans. Having a musical ear does not make you stronger nor more fertile, but it helps you play the guitar, which sure is sexy.

Being capable of throwing a rave without the need of glow sticks could be another form of sexual display, and if so, the shinier people would be positively selected.

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    $\begingroup$ One important thing is that bioluminescence only works in the dark (you just can't overpower the sun), so you'll need something that makes humans more active at night (potentially only for mating?) or in dark areas (caves etc). $\endgroup$ – Nicolai May 31 '18 at 14:31
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It would be plausible for communication only in absence of verbal language and (maybe) facial expressions. Since humans have language and no-verbal communication (posture, tone, volume of voice, facial expression), there is no need of another communication system. Facial expression in your case is not needed, because bio-luminescence develops in darkness.

It would be plausible for attraction. But this kind of solution for attraction usually happens only in enviroments with abundant resources (darkness isn't a place with abundant resources), where a species can waste effort for attraction. That is why birds in jungles are more colorful than birds in tundra.

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  • $\begingroup$ "darkness isn't a place with abundant resources" - which is why deep sea life relies pretty much solely on bioluminiscence... $\endgroup$ – John Dvorak May 30 '18 at 19:51
  • $\begingroup$ Indeed @JohnDvorak . But in this case the specie is a human-like one, that lives in land, not sea. $\endgroup$ – Santiago May 30 '18 at 20:05
  • $\begingroup$ In some ways verbal communication is less important than non-verbal. Words are good for transmission of ideas and when technical or particular information needs to be conveyed, but in general the non-verbal aspects of interaction between two humans are what get the message across. Think of sarcasm, or how a threat can be made to sound more threatening when polite words are used rather than hostile words. $\endgroup$ – Asher May 31 '18 at 22:30
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Yes but you'll need a more passive predation scheme than what our ancestors had to deal with on Earth, certainly when it comes to nocturnal hunters. That's assuming that the "humans" in question always glow to some degree, if they can shut it down completely, or better yet it shuts down when not in active use then it shouldn't make much difference at all to the human condition not in terms of evolutionary pressure.

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