wow that is really interesting.  My son was born with a bright red strawberry birthmark on his knee, 3 bright red dots on his back and a little mark in the corner of his eye.  The one on his knee has faded, as the one by his eye, you cant see them anymore, he just has 3 tiny dots on his back.

My daughter has none!

My kids father had no birthmark, i have a faint dark one on the back of my leg.  I dont think they are genetic like freckles or moles, which are more likely to be because of your skin type.

I think they can be both. some from genetics. My daughter has one the same shape, color, and size as her father in the same spot on her leg. as well as due to past lives. i have no memory of past lives, but i believe i've had some before, and it would make sense that a scar or wound could show up as a birthmark in later lives. in some cases though birthmarks are a due to something else, both of my brothers have ones that are cause by something else, one has a skin pigmentation disorder(?) that causes patches of skin on his body to be lighter than his natural skintone, he has been told that it may eventually cover his entire body, for now its mostly on his neck and some of his chest, he even has a white streak of hair right behind his ear where it goes into his hairline, and his hair is naturally dark brown. my father has the same thing. my other brother has a small depression in the middle of his back between his shoulder blades about the size of a pencil eraser. it is what is left of a blood blister he had at birth, to begin with it was a small red dot that grew to be as big around as it is now and looked like a blister full of blood, he had to be careful of it so as not to pop it, it gradually faded and now just looks like a scar of sorts.

i in no way think birthmarks are evil, even when they take on a sinister appearance or some "dark" symbol.

just my thoughts, take them as you will.