The concept of trust isn’t brought up anywhere in the passage. So there’s no support that the author believes the Ultimatum Game requires strangers to trust each other.

The author never suggests that the Ultimatum Game has overturned the assumption that people make economic decisions primarily out of rational self-interest. It’s possible that people still make economic decisions primarily out of self-interest, but with a few exceptions.

The author doesn’t suggest that the results of the Ultimatum Game are unpredictable. In fact, the evidence shows we can predict at least some of the behavior — we get statistics about typical behaviors in P2. Two-thirds can be expected to offer between 40 and 50 percent. Only 4 in 100 offer less than 20 percent.

Supported. In P4, the author endorses the explanation that our emotions have been shaped by living in small groups, where we engage in repeated interactions with others. Because of these repeated interactions, we needed to respond angrily to low offers when splitting resources, or else we’d get a reputation for accepting low offers. The author believes this emotional tendency carries over to the Ultimatum Game, because our emotions don’t discriminate between one-shot, anonymous interactions and repeated interactions. The way we responded to repeated interactions as we evolved carries over to the one-shot, anonymous interaction in the Ultimatum Game.

The author doesn’t view the Ultimatum Game as “proof” that our emotions have been shaped by living in small groups. Rather, the author offers the hypothesis that our emotions have been shaped by living in small groups as an explanation for the results of the Ultimatum Game. The behaviors observed in the Ultimatum Game are a phenomenon that the author tries to explain. But they are not proof of the author’s explanation.