What was the explanation for the evolution of altruistic behavior in the vampire bat example discussed in class

Mike and his wife, amanda, are arguing about his in-laws. mike doesn’t want them to visit because they fight all the time when they come to the house and he is worried about the effect that their fighting is having on mike and amanda’s children. amanda finally yells out: “what about our fighting? ” mike replies, “well, that’s different. we fight because we’re having a disagreement, they fight because they hate each other! ” this is an example of