[johncole]

+1. I read an anthropology article years ago that helped explain this from an evolutionary point of view. Men tended to make strong bonds with a few men for life, while women tended to have more mobility in their bonding. Men needed intense trusting relationships that their lives depended on: if you're going to organize and go hunt big animals, you needed to trust those you went with. Women needed different things during different periods of their lives. Vulnerability really is the need for community to help raise children. So you made friends maybe before you had children, then different friends who were also raising children, then you made different friends and had different relationships when you were finally a grandparent and not having children yourself.