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> It must be important if it was worth evolving white skin over Where is the evidence that we evolved white skin to produce more vitamin D? Light skin in Europ

• 0-_-0 6y ago
  From the article you linked: "A sun lower in the sky and shorter day lengths would have favored skin that more easily synthesized vitamin D." The article also points out a correlation between latitude and light skin, so the evidence is pretty strong (based only what you linked) for why light skin evolved.
  • tchaffee 6y ago
    If you look at the full quote, the purpose is not to confirm your theory but to inject healthy doubt in your theory: "A sun lower in the sky and shorter day lengths would have favored skin that more easily synthesized vitamin D. But researchers are now learning that other factors must have been at play." > The article also points out a correlation between latitude and light skin Well yes, exactly. Correlation. I asked for causation, which it seems you are still lacking.
    • 0-_-0 6y ago
      I read the article but failed to see what doubt it sheds on the idea that light skin evolved to increase vitamin D production. Could you help me find it please? You asked for evidence of causation, which I provided. Correlation of latitude with skin colour is evidence of causation. Light skin colour providing vitamin D while increasing skin cancer risk is evidence of causation. No other known advantage of light skin colour existing is an evidence of causation. Taken together, there is strong evidence of a causative link between the evolution of white skin and vitamin D production.
      • tchaffee 6y ago
        > Correlation of latitude with skin colour is evidence of causation. Correlation is not causation. I'm sorry but I don't think you have any evidence at all that lighter skin was caused by a need for more vitamin D. It's just an educated guess on your part. Lighter skin could have just as easily been an adaptation related to less visibility to predators and prey in snow. Like the article I cited said "researchers are now learning that other factors must have been at play." And with the article that started this thread we now have quite a few studies telling us that vitamin D supplementation doesn't do anything helpful. So why would humans undergo an adaptation that provides no benefit? Perhaps exposure to the sun provides health benefits? Or is it that healthy people get outside more and therefor have higher vitamin D levels? I'm happy saying "I don't know" and asking more questions. I encourage you to do the same instead of claiming causation when all you have is correlation.
        • 0-_-0 6y ago
          Correlation is not causation, but you didn't ask for proof, you asked for evidence, and correlation is evidence. For example, do you know whether smoking causes cancer? Because all the evidence we have that it does is based on correlation. Or you're happy saying "I don't know" and asking more questions? How would you show a causal link between vitamin D deficiency causing the evolution of light skin colour without being able to conduct a double blind study? It's fundamentally impossible to prove, all we have is evidence, which is this case is sufficient to say as the first sentence in Wikipedia [1]: "An abundance of clinical and epidemiological evidence supports that light skin pigmentation developed due to the importance of maintaining vitamin D3 production in the skin" [1] https://en.wikipedia.org/wiki/Light_skin#Evolution https://en.wikipedia.org/wiki/Light_skin#Evolution
          • tchaffee 6y ago
            > you didn't ask for proof, you asked for evidence I didn't ask for evidence from you. I asked more specifically "Are there any studies giving strong evidence as to the causation for evolving white skin? > do you know whether smoking causes cancer? Because all the evidence we have that it does is based on correlation. That's wrong. We understand why smoking causes cancer. Just for example one of chemicals produced by tobacco smoke is benzoapyrene which is a DNA disruptor, producing mutations that can lead to cancer. [1] > It's fundamentally impossible to prove, all we have is evidence. That's progress. We've gone from "It must be important if it was worth evolving white skin over" to "we can't prove that's why we have white skin". The Wikipedia sentence claims an "abundance" of evidence and then only gives one source, which is behind a paywall. So I'm going to recommend an edit to that article to either give more sources or change the "abundance" claim. Furthermore just a few sentences later it contradicts itself with this: "This accounts for the development of dark skin pigmentation of people living near the equator but does not account for the increasingly lighter-skinned people living outside the tropics." Yet more doubt as to why we have white skin. From your source. Finally, the article that started this discussion provides strong evidence that our need for vitamin D is less important than we previously thought. For sure very low levels of vitamin D are dangerous. But the link between vitamin D and health could be reverse causation: sick people stay inside and therefor have less vitamin D. It could also be that exposure to sun provides something more important to health than vitamin D that we are not aware of yet. So the claim that we evolved white skin just for vitamin D is increasingly on less stable ground. I'll stop here because I'm happy that you've gone from what seemed like a factual claim to you claiming that it's something we cannot prove. Who knows, maybe someone clever can prove it. But it sure does seem like the evidence itself (about both vitamin D and skin color) is fairly rapidly changing. [1] https://www.mskcc.org/news/how-do-cigarettes-cause-cancer https://www.mskcc.org/news/how-do-cigarettes-cause-cancer