The piece of evidence that would most likely weaken the argument for kin selection driving altruistic behavior in groups of related individuals is:
Data showing that only distantly related individuals are most likely to perform altruistic behaviors in order to protect each other.
This evidence suggests that altruistic behaviors are not restricted to closely related individuals, as would be expected under kin selection. Instead, it indicates that altruism can occur among unrelated or distantly related individuals, thereby challenging the notion that kinship alone drives altruistic behavior.