For the following stars

-A Class

-F Class

-G Class

-K Class

-M Class

What are the most likely skin tones for each type of stellar class? Also for their eyesight how different is it to vary for each class of star? assuming the planet orbits at a distance to its star so it recieves the same amount as sunlight Earth does, also that the planet is Earth sized with similar gravity.

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    $\begingroup$ You need to also include some information about the composition, size and distance of the planet from its star. You would also need to consider the fact that skin types of creatures which have appeared in the evolutionary history of Earth (and some still present) are so vast that you cannot simply generalize skin type and tone by the planet type. I do not mean to disappoint you or put your down, but your question appears to make an immensely generalized and simplistic view of star type on the skin of creatures appearing on its planets. $\endgroup$ – Youstay Igo Mar 26 '16 at 10:33
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    $\begingroup$ I agree with Youstay Igo, you should give more information. Also, I think you should split this into two questions, one about eyes and the other about skin tone. $\endgroup$ – Xandar The Zenon Mar 26 '16 at 16:28
  • $\begingroup$ We need to know if you're taking about humans colonizing such planets, or if you're talking about what sort of life would evolve there. In our evolution, animals evolved to use melanin to block UV light, but note that plants don't. Alien evolution may, like plants, not use that sort of evolutionary adaptation at all. $\endgroup$ – Lensman Mar 29 '16 at 6:30
  • $\begingroup$ Eyes have evolved multiple times in Earth's evolutionary history. It would be a mistake to assume aliens' eyes resemble ours, or that our vision systems work similarly. Note a fly's eyes work very differently than a human's or an octopus's. $\endgroup$ – Lensman Mar 29 '16 at 6:33
  • $\begingroup$ I highly recommend reading Dole's HABITABLE PLANETS FOR MAN. Dole gives scientific reasons why we won't expect to be able to colonize worlds around A or M class stars, and as I recall, he thinks about half the range of F class is also uninhabitable. However, there may be some exceptions to his rules. For example, a twin planet (rotating about a common center of gravity) may be possible as a stable configuration in the habitable zone of an M class star system. Fortunately, Dole's book s available as a free .pdf: rand.org/content/dam/rand/pubs/commercial_books/2007/… $\endgroup$ – Lensman Mar 29 '16 at 6:40

You have stated a fairly similar environment for your humanoid species which we have here on Earth. Does this mean that your humanoid species will have eyes and skin types resembling us?

No, not necessarily. It is possible, but not compulsory.

A Brief Overview Of Evolutionary History Of Eyes

Scientists believe that eyes first appeared in creatures known as trilobites. They had a vast variety of eyes (some even having eyes with fixed, hard-crystal lens instead of adjustable lens!). They had compound eyes (one eye with several lenses) and their main purpose is considered to be (probably) detection of movement, instead of clear and distinct view of their surroundings.

All vertebrates (creatures with backbones, including fish, amphibians, reptiles, mammals and birds) have common origins in the forms of primitive chordates such as Pikaia, Myllokunminjia and Hykoichthyes.

Mammals appeared in the evolutionary history some 215 million years ago or so during late Triassic Period. Mammals were confined to a nightly life (nocturnal) which led to refined hearing sense but (compared to reptiles) low resolution vision. Birds in particular are thought to have a far superior vision than mammals.

Eyes Of Humanoids On Your Planet(s)

The type of eyes on the human(oid)s on your planet depends solely on the evolutionary history of life on your planet. I am assuming that you are not going to provide with a long story of the evolutionary history of life on your planet, so you have a pretty large spectrum of eyes to choose from. Here are some considerations:

  • you can give your humanoids compound eyes like those of insects if your humanoids live (or have lived for long) in caves and/or underground residences where sunlight reaches in minute quantities.

  • you can give your humanoids very powerful, high resolution eyes (like eagles) if your humanoids have lived as dominant species in sunlight for a long time (at least a hundred million years).

  • they can have eyes like us (useful for reading and close range focus, but not very useful for identifying small things -beyond 600 meters) if they have had an evolutionary history like us.

  • you may give them just one eye if the elements required in eye construction are too scarce on the planet to afford building two eyes.

  • or you may want to give them solid crystal eyes (like the trilobites which had calcite eyes) which would focus the image by moving the lens forward and backward, instead of making the lens thick or thin (as happens with birds, reptiles and mammals).

Features Of Skin And Their Functions

There are some features of skin which I should explain to you, so that it would make it easier for you to choose what type of skin you should render to your humanoids.

  • skin provides a boundary to your creature and helps keep body fluids (like blood) inside it.

  • skin also provides the first (and very potent) line of defense against shock damage to your body. This means that if your humanoids are living in an environment where they have to involve in fights (infighting or fighting against animals), there are major chances they would have a thicker or otherwise stronger skin.

  • if your world does not have any ozone layer, the skin would also have to shield the innards from disastrous ultraviolet radiation. I have not researched about it in detail, but I think it would lead to a darker colored, thicker skin (think about a human with dark gray or black skin as thick as a rhinos).

  • the hair on mammalian skin provide them with a covering against cold weather. This is why you have mammals successfully living in north pole (foxes, rabbits, lynxes etc) where there are no reptiles or amphibians. Humans on planet Earth started losing body hair about the same time they started covering themselves up with animal hides (for protection against cold).

  • amphibians can breathe through their skins. For this, their skin is highly permeable (if you paint a frog with poison, the poison will be absorbed by the skin into the blood and it would die). If you want to give your humanoids this ability (breathing underwater) you might want to give them this type of skin. However, remember that permeable skin is much thinner and weaker than impermeable skin.

  • reptiles have a scaly skin and they cannot absorb any chemicals through their skins. Mammalian skin can absorb chemicals, but this ability is very low as compared to amphibian skin. However, the scales of amphibians (think of snakes) make them more resistant to scratches and bruises against rough surfaces.


The type of skin and eyes/vision your humanoids have, depends more heavily on the individual evolutionary history of life on the planets, instead of the type of star (as long as the planets are all located in the habitable zone and are getting equal amounts of light).

As such, you have a vast option of skin and eye types to choose from, depending on the environment of your humanoids. For example, humans living perpetually in catacombs and cave systems would not have as sharp vision as those living in the open because less light reaches in the caves, making hearing more relevant and beneficial sense than vision.

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    $\begingroup$ I have one minor issue: "Humans on planet Earth started losing body hair about the same time they started covering themselves up with animal hides" Yeah since humans mostly evolved for hot savannahs I think you're kind of missing something obvious (The fact that african bushmen don't wear a lot of clothes is telling)... Humans more likely lost body hair because we evolved to be able to sweat to shed heat more efficiently than other mammals. We could chase them until they collapsed from heat exhaustion. As far as mammals go we are among the best at endurance running in hot environments. $\endgroup$ – Vakus Drake Mar 28 '16 at 7:49
  • $\begingroup$ That is correct @VakusDrake But you are oversimplifying the facts. We could hunt African game is a big generalization. 90% of the people living on the world today aren't marathoners and wouldn't be able to sustain the same speed in running over large distances (dozens of miles). $\endgroup$ – Youstay Igo Mar 28 '16 at 12:44
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    $\begingroup$ Yes but my point is that nearly all of human physiology did evolve to do that. Whether we do that anymore is irrelevant since this is about evolved traits. My point was that saying humans lost fur because we got clothing isn't even a little true. $\endgroup$ – Vakus Drake Mar 28 '16 at 13:18
  • $\begingroup$ @VakusDrake: no, you cannot say it plainly that sweating (which is linked to loss of hair) provided all humans long distance stamina running. Even all humans in Africa are not capable of the stamina hunting which some tribes do. Where is the evidence that all humans could run for long distances with the same sustained speed? It is only a theory, not a proven fact. $\endgroup$ – Youstay Igo Mar 28 '16 at 17:32
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    $\begingroup$ You miss the point: Modern humans don't matter for this example, nearly all our evolution happened in a portion of Africa. As a result most of our traits are a result of what would help a gene propagate itself within a population of african hunter gatherers. And regardless of how much much of a role sweat had on hair loss, since we didn't rely heavily on clothing in the environment we evolved for, we can conclude that clothing probably didn't drive that traits evolution. $\endgroup$ – Vakus Drake Mar 30 '16 at 2:47

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