I think that the self interest is never truly lost but in order to gain self interest one realizes the values (external subjects) are interactive and can be advantageous to fulfilling the self interested motives. At the start of the thread Ruthless, you drilled into our heads the motive is self interested, and altruism can therefore not be a truly direct motive or else it'd be irrational. So the behaviour looses its linearity via the indirect motives of altruistic motives with external interactive values (interactive in the ability to reciprocate, interact), eventually propagating back to the self interest "vector" if you will(which in a one dimensional/linear behavioural system would have been direct)
Why not just a direct self interest behaviour or motives? Well behaviour says otherwise. I'm sure you can think of plenty of situations in which this behaviour can be seen, but just in case.
BBC - Science & Nature - Mammals - Reciprocal alturism
The classic prisoner's dilemma: This shows that intellect and ignorance (cognitive evolutionary traits) would effect the outcome of the decision to fulfill the self interest. If you google it and read about it you'll notice that self interest is always in the people's minds, but their behaviour is not linear to self interest, rather, there are conflictions. Its kind of like saying that on a society one cannot fulfill their self interest with some simple harmonic set of conscious reactions.
I dunno, maybe I don't quite understand what you mean by linear but do you not see that humans can only try in social interaction to indulge as directly as possible their self interest . There is going to be a requirement to motivate oneself to be altruistic to maintain a self interested virtue.
To put it another way, do you honestly think that if we did not hold some emotional or logical appeal for motivation of altruistic actions knowing even instinctually that they'd lead indirectly to fulfilling self interest that humans would behave altruistically?
Is this what you were refuting??