Vitamin D is vital to health. It helps to build strong bones and teeth, boosts the immune system, fights cancers, and nourishes the heart. It is thoroughly good stuff. We can get it in two ways—from the foods we eat or through sunlight. The problem is that too much UV exposure damages DNA in our cells and can cause skin cancer. Getting the right amount is a tricky balance. Humans have addressed the challenge by evolving a range of skin tones to suit sunshine intensity at different latitudes. When a human body adapts to altered circumstances, the process is known as phenotypic plasticity. We
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