> Overall, I think the scales are clearly tipped against fidelity. It may
> work well for some small fraction of the population, but I expect that a
> large majority of us would be better off with some alternative system.
There's a long list of pros to marital fidelity not mentioned here, but I agree that moral actions--not values themselves, merely the actions one takes to support them--have to change with technology, and the problems that will arise from our failure to structure our society with that in mind will greatly increase. The destructive points of marriage are mostly not the institution itself--freely entered contracts creating mutual obligations for mutual benefit are the very foundation of civilized behavior--but rather the cultural and legal baggage that surrounds it.
The primary technological changes that affect the usefulness of marital fidelity are birth control, medicine, and general economic growth. Throughout most of human history, children wouldn't eat unless they had two healthy adults caring and providing for them; so a mother had a great interest in securing the promise of food and protection for her children, and fathers had an interest in ensuring that their investments were actually going into their own children. Today there is reliable birth control, so purely recreational sex is possible--which it never was during the time of our evolution. Secondly, economic growth makes it common for a child to have more than adequate care from one parent. Today we know about the evolutionary source of kin-preference and can overcome it (I would probably care for stepchildren, for example, rather than killing them as my ancestors would).
I've always though something like Heinlein's "line" marriages would be better suited to a modern society. Plenty of people around to pool resources, care for children, and have some degree of sexual variety while keeping intimacy and maintaining a history and consistent values.
-- Lee Daniel Crocker <email@example.com> <http://www.piclab.com/lcrocker.html> "All inventions or works of authorship original to me, herein and past, are placed irrevocably in the public domain, and may be used or modified for any purpose, without permission, attribution, or notification."--LDC