Applying semi-formal logic to plot out human behaviour is a dangerous game. Most of the time the analysis will fail based on the lack of an appropriate model. I think there are many more scenarios involved in each of the LDR types, but to prove it, I will give you one, which I think is probably one of the most common.

4. Even though your original partner had previously met your needs better than a new partner will ever meet them, you get tired of having your needs met to a lesser degree, so you go for the new partner and have your needs met more fully, but not as well as your original partner would have.

Basically, you're impatient. Anyway, I think there are several other scenarios I could add. One last thing: you are operating under the assumption that love is an aggregation of fulfilled needs. Even though this is probably a large part of what makes someone more or less attractive, it doesn't account for any sense of attachment or dedication. For instance, you meet a person and they begin meeting your needs; you are with them for 2 years and they fulfill just as many of your needs, yet you probably have a greater degree of dedication and commitment (read, are "in love"). Accounting for this would drastically complicate your scenarios. People don't operate optimally either, probably because we have such short lifespans.

OTOH, I'm very skeptical of any LDR. I'm assuming that this conversation came up because someone is considering undertaking one. Let me offer my advice: I would make sure you are in love with that person, whatever that means to you--and perhaps during the process you should re-examine what it means to be in love. I would also do it all out. Meaning, if I was going to make a commitment, I'd do it balls-to-the-wall DSOP. Of course, if either you or your partner find another, you can call the whole thing off at any time. Some things during that time suck, but hopefully you get over it.

Yeah, you have a point about time being a factor. Whether you've been with a partner for a few months or a few years can make a difference. I thought about trying to incorporate this by considering "investment" as part of the model. Basically, if you've been with someone for a few years, you have a lot invested in the relationship, and thus are more likely to stick with the relationship. That's why people sometimes stay in crappy or abusive relationships if they've been with the person for a long time.

However, I think investment is taken care of in my model. If you've invested a lot of time in someone, then presumably they are going to be able to meet your needs much more effectively than someone you've just met. Therefore you shouldn't really have to worry about them finding someone better.

I agree with Kurt. One thing in particular that your model does not take into account is that human beings have an adverse reaction to others horning in their mates - independent of the threat of losing them. Exclusivity is, in and of itself, a need that must be met (especially in guys).

Mind you, this is human nature. It's built into our instinct and can't be consciously reasoned away.

Assuming Jane and John are our couple in question, SOP LDRs still allow for the situation where Jane sees Bill during separation, but still chooses John after separation. In this case, John’s exclusivity need would not have been met, and even though he still has Jane, he would be worse off than if Jane had never seen Bill at all.

Because DSOP LDRs would presumably prevent this situation, guaranteeing exclusive access, they do have advantages that you aren't taking into account.

Interesting article. I'd be interested to hear the major arguments in the book.

Three major criticms of your model, though:
(1) I agree with the above comments re the effect of jealousy. Due to one or both partners' jealousy, it's far from clear that an "after" SOP relationship will be the same as before. Seeing your partner can easily move to someone new may make you doubt his commitment.

(2) Your partner may or may not get back with you, even if you are superior to his current partner. Depending on the level of commitment between these people, they could stay together if some minimum level of needs was met. (and your partner did not want to hurt his new partner.)

(3) The concept of commitment is never really defined. I would argue one is not very committed if he must "see other people" in the first place. To me, commitment implies a bit more than fulfilling needs. I assume your concept of needs includes more than physical needs, but it's hard to remain committed to anything if it's all boiled down to a list of needs. (that can be met by others.)

OK, good point with jealousy. But my article is more prescriptive than descriptive. Jealousy is a behavior that is a product of evolution. How useful are our current behaviors with respect to jealousy? I can think of some evolved behaviors that were important at one time, but that are no longer very useful (e.g., eating food whenever you see it, even if you aren't hungry). Back when we lived in caves, long distance relationships couldn't exist. Technological changes have made them possible. Have our behaviors changed to match?

Same types of arguments apply to commitment. What is the purpose of commitment and do our old notions of commitment make sense any more?

Perhaps there isn't a purpose per se to jealousy or commitment. However, that does not negate their existence.

More to the point, though, I thought your model was based on a committed relationship. As long as the members of the relationship want to be committed to one another, then the notions of commitment matter very much.

How would they affect the human species biologically? Perhaps committed relationships make for more stable families and better raised children. I don't know. As long as people choose to commit themselves to relationships, though, I think the concept is relevant.