Extreme self-sacrifice towards the ingroup may be adaptive if a hostile outgroup threatens the entire ingroup.
ɛkstɹˈiːm sˈɛlfsˈækɹᵻfˌaɪs təwˈɔːɹdz ðɪ ˈɪŋɡɹuːp mˈeɪ biː ɐdˈæptɪv ɪf ɐ hˈɑːstəl aʊtɡɹˈuːp θɹˈɛʔn̩z ðɪ ɛntˈaɪɚɹ ˈɪŋɡɹuːp.