Inhabiting my earth-like world will be humanoid beings that have a skin tone that is as dark as Vantablack. Let's assume these human-like beings share the same ancestry as humans and we can safely assume cognition and physique to be identical to humans. The only difference being their skin is naturally as dark as Vantablack (well techinically, this may require some inner workings, like bio-mechanics, to be different as well). While Vantablack is not actually a color but rather a material, it's still the closest thing known to man to the effect I want to create in my world, and so as not to use the word inappropriately, I will just coin my own word for these fantasy humans: Vantaman. While the darkest known pigment of us humans has not been scientifically documented, I did want to provide a frame of reference. From a crude1 series of image analyses I got the hex color: 1f1b1a for very dark-skinned homo sapiens. Hex colors, however, can't do Vantablack justice. Vantablack is often described as the closest thing to looking into a blackhole as we can get. It absorbs 99.97% of light. Here is a Vantablack material demonstration, both busts are identical in shape:
Actual human skin pigment evolutionary narrative
To help us tackle the task of how Vantaman came to be, it may be helpful to understand how actual humans took on the adaptation of dark skin in the first place. According to the understanding of human evolution at the time of this post, humans began to develop dark skin pigments through natural selection about 1 million years ago. The context for this adaptation was these hominids were beginning to move into environments that offered little to no protection from exposure to the sun -- the Savannah. It was at this point that the hominids began to have less and less body hair and began to develop perspiration as a means of cooling down. And it was at this time that humans began to take on the trait of having dark skin. The darker skin helped protect the bio-mechanics needed for healthy hominids. With only vestigial body hair, the hominids with lighter skin could not provide sufficient protection for embryogensis and so the melanin-dense darker skin was naturally selected to deal with harmful UV radiation. (it's thought that they would conceivably face DNA degradation as well). Of course as later descendants left this environment and ventured to, say, Europe, where humans embraced a more troglodytic lifestyle, then skin pigments became lighter to allow our livers to synthesize vitamin D more easily. And the rest is history.
With all that in mind, it's all the more challenging to conceive of an evolutionary narrative to explain a vantablack skin pigment trait. Why would Vantaman need to absorb 99.97% of light?
My first inclination was to keep the narrative and up the ante; Vantablack pigment to cope with a sun that emits far more radiation than our sun. I lacked the knowledge of astrophysics to gauge whether such a world would still be earth-like my hunch was no. However maybe someone more knowledgeable can come up with some special case scenarios and revive this solution.
However the question is not only concerned with stellar emissivity -- anything rooted in science is fair game. To help maintain a reasonable scope, here is a quality metric:
Quality Metric: The closer to earth-like your evolutionary narrative for Vantaman is the better2. If it turns out there is no earth-like solution in the truest sense of the word, then I can still accept an answer as long as it's scientifically plausible. Earth-like is ideal though; I don't want to go nuts with mother nature unless it's really, really necessary.
- Even though we have not seen Vantablack in biology, we are assuming its possible; how the heck it works is out of scope. It could be nature's version of vertical carbon nanotubes or something else. Whatever it is, it is as dark as vantablack. Point being, it's not a xenobiology question.
- Assume the vantablack pigment trait requires negligible energy resources
- In this question, "earth-like" is not used in the most rigid sense. Flora, fauna and celestial bodies are earth-like in terms of initial conditions, but you may change them as per your answer's needs. Bear in mind the quality metric favors fewer or smaller changes.
- The orifices of Vantaman: mouth, eyes, ect, do not have to be vantablack.
- The evolutionary narrative is concerned only with prehistoric-times, we don't have to worry about high technology -- humans won't invent nano-tech for a million years
- Unless it's vital to your narrative, you don't have to provide an exhaustive nutrition plan for Vantaman, you can assume nature allows him to synthesize nutrients like vitamin D some other way. This assumption is optional, because it's related to the main problem, but I don't want to impose undue work for the answerer
- Ideally, we provide a narrative for Vantaman that revolves around blocking UV rays. However, if it this is a dead end, you may propose an alternate evolutionary need for vantablack skin.
1. crude because images not robust to different lighting or other external factors, but I did my best and averaged the hex value
2. I think this is a reasonable quality metric; we can quickly tell what's plausible on Earth, but we are on the honor system to an extent. For example, who is to say what's more outlandish: UFO's beaming lasers at Vantaman to be dark or having billions of tiny blackholes continuously forming and decaying to create Vantaman's skin. If it comes down to this, we'll just have to use another metric: what is there documented evidence of?