The piece of evidence that would be most likely to weaken the argument that altruistic behavior in groups of related individuals is primarily driven by kin selection is:
Data showing that only distantly related individuals are most likely to perform altruistic behaviors in order to protect each other.
This evidence challenges the notion that kin selection (which relies on shared DNA) is the primary driver of altruistic behavior, suggesting instead that altruism can occur and may be more prevalent among individuals who are not closely related, undermining the argument's premise.