Altruism, by diverting resources from the altruist, can act as an "honest signal" of available resources and the skills to acquire them.
ˈɔːltɹuːˌɪzəm, baɪ daɪvˈɜːɾɪŋ ɹᵻsˈoːɹsᵻz fɹʌmðɪ ˈɔːltɹuːˌɪst, kæn ˈækt æz æn "ˈɑːnɪst sˈɪɡnəl" ʌv ɐvˈeɪləbəl ɹᵻsˈoːɹsᵻz ænd ðə skˈɪlz tʊ ɐkwˈaɪɚ ðˌɛm.