But suppose eight of the nine of you are blond, and one is a brunette. The brunette is now a Schelling point. If you choose to kill and eat the brunette, there's a pretty good chance all of your blond friends will do the same, even if none of you had a pre-existing prejudice against brunettes. Therefore, all eight of you shout out "Let's kill and eat the brunette!", since this is safer than drawing lots. Your lifeboat has invented in-group bias from rational principles.

Suppose further that you have green eyes while everyone else on the boat has gray eyes.

Maybe you don't want to go down this road after all.