The only difference between inner conflict and outer conflict is that we draw a line somewhere and call things on one side of that line "inner" and on the other side "outer".
With a little modeling of the other, and communication, peace could be achieved, and pleasure maximized, between Ugg and Ogg:
Ogg "I value my harem"
Ugg "And I value mine"
Ogg "I think I'll take yours, too"
Ugg "If you try that, I'll bash your skull in"
Ogg "Not if I bash yours first"
Ugg "So attack me then. You might get my harem, you might die. The law of diminishing returns says my harem won't bring you as much pleasure as you stand to lose if you lose yours. The NPV of your war is, for you, negative."
Ogg "Wow, you're right. Truce?"
So maybe Ogg "wants to bash Ugg's skull in" but in reality he doesn't want to TRY. Ogg doesn't have freedom to choose whether he bashes Ugg's skull in, but rather he has the freedom to choose whether he TRIES to bash Ugg's skull in.
When navigating a reality in which you can be thwarted, others' pleasure is your pleasure, no matter how "selfish" you are.
Intersubjective selfishness, when combined with communication and policy modeling, becomes objective group-pleasure maximization.
Given years and years and years of this sort of interaction, perhaps Ogg (if he wasn't born with it) would start to develop an innate sense of "goodness" arising from his belief that Ugg would be benefiting from a situation. It's a form of caching, really. Instead of having that same conversation each time, by now Ogg understands that Ugg understands that Ogg understands that Ugg understands that Ogg understands that Ugg aint' takin' no shit laying down. Eventually, all repeated thought processes become unconscious. So eventually the only conscious content of Ogg's mind is:
Ogg: "I bash Ugg's head in an take his harem!"
Ogg; "But that would be bad for Ugg"
Ogg: "Better not then"