My eyelids are swollen/drooping?

How come some asians have double-eyelids while some don't?

• what causes some asians to have double eyelids and some don't? is it the muscles and bone structure? i know there is a reason. strangely enough one of my eyes is double eye lided and the other is monoeyelid. so explain that. there has to be something physically different on one side of my eye. like maybe the bone or the muscle around the eye. so why do some asians have double -eyelids and don't. cuz i have expereienced both words. one eye is double eyelid and the other is single. why is that? and lately. i'm waking up with both eyes with double eyelids. now it seems like double eyelids is the norm for me. and on rare occasions it reverts back to single eye lids on one side. i my self am an asian. i'm asking this in the anthropology section so i don't need any racist comments.

• Answer:

  According to this article, it has something to do with muscle attachment. I have heard that it likely evolved in response to cold winds in the Asian steppe or perhaps to protect the eyes from sun. http://en.wikipedia.org/wiki/Epicanthal_fold