I also wonder if longevity is having a secondary effect, in that
there are more grandparents available to help raise children:
a woman who might once have stayed with an unsatisfactory
man because she had to feed her kids is increasingly likely
to be able to go back to her parents (or to one of them, if
they're no longer married), and at least have a roof over her
head, and possibly someone to watch the children while she
earns a living. And those parents, however much they might
prefer their daughter to stay married, are acting in their own
evolutionary interests by giving her and her children--their
grandchildren--shelter.
Vicki
rosenzweig@hq.acm.org
http://members.tripod.com/~rosvicl