OK, I just made a search and found this article for you... :)

http://www.livescience.com/9487-women-pick-mates-flings.html

I didn't read the whole of it but in the beginning it says it all:

"Women seem to judge potential mates by how masculine their features are, new research shows. Men with square jaws and well-defined brow ridges are seen as good short-term partners, while those with more feminine traits such as a rounder face and fuller lips are perceived as better long-term mates." :)