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One of the difficulties of digital photograph is that it does not handle shadows very well and needs some assistance.  I am sure that your subject had very dark skin, but your eyes will allow you to see more detail in that skin in reality than the photograph you post.  I suggest that you use the simplest of adjustments in the various computer programs, usually called "fill" or "dark fill" or "black fill" or similar to bring the tones of the shadows up enough that we can see some detail in those dark shadows.