Some researchers have claimed that group selection theory is required if we are to explain why people have the capacity to behave generously, nicely, and morally to other members of their group, whereas the selfish side of human behavior has been caused by natural selection. Why is this claim inaccurate?

These researchers are confusing the every-day meaning of selfish with the evolutionary meaning; if generous behavior is adaptive, then it is also selfish in evolutionary terms.

Explanation:

From their claim, it is clear that the researchers are simply confusing the general meaning of selfishness with the evolutionary meaning. This means that generous behavior isn't adaptive, because if it is, then it is okay to say that generous behavior is also selfish when defined from an evolutionary point of view.