A related concept in descriptive ethics is psychological egoism, the thesis that humans always act in their own self-interest and that true altruism is impossible.
ɐ ɹᵻlˈeɪɾᵻd kˈɑːnsɛpt ɪn dᵻskɹˈɪptɪv ˈɛθɪks ɪz saɪkəlˈɑːdʒɪkəl ˈiːɡoʊˌɪzəm, ðə θˈiːsɪs ðæt hjˈuːmənz ˈɔːlweɪz ˈækt ɪn ðɛɹ ˈoʊn sˈɛlfˈɪntɹɛst ænd ðæt tɹˈuː ˈɔːltɹuːˌɪzəm ɪz ɪmpˈɑːsᵻbəl.