Why The Underdog?

From a group blog focused on human rationality:

When you put people in a social-science experiment room and tell them, in the abstract, about the Israel/Palestine conflict, they are in “far” mode. This situation is totally unlike having to choose which side to join in an actual fight – where your brain goes into “near” mode, and you quickly (I predict) join the likely victors....

In a situation where there is an extremely unbalanced conflict that you are “distant” from, there are various reasons I can think of for supporting the underdog: but the common theme is that when the mind is in “far” mode, its primary purpose is to signal how nice it is, rather than to actually acquire resources. Why do we want to signal to others that we are nice people? We do this because they are more likely to cooperate with us and trust us! If evolution built a cave-man who went around telling other cave-men what a selfish bastard he was... well, that cave-man wouldn't last long.