Plato, Laws 773b

προθυμεῖσθαι γίγνεσθαι κηδεστὴν τὸν αὑτῷ συνειδότα ἰταμώτερον ἅμα καὶ θᾶττον τοῦ δέοντος πρὸς πάσας τὰς πράξεις φερόμενον· τὸν δʼ ἐναντίως πεφυκότα ἐπὶ τἀναντία χρὴ κηδεύματα πορεύεσθαι. καὶ κατὰ παντὸς εἷς ἔστω μῦθος γάμου· τὸν γὰρ τῇ πόλει δεῖ συμφέροντα μνηστεύειν γάμον ἕκαστον, οὐ τὸν ἥδιστον αὑτῷ. φέρεται δέ πως πᾶς ἀεὶ κατὰ φύσιν πρὸς τὸν ὁμοιότατον αὑτῷ, ὅθεν ἀνώμαλος ἡ

sprung from steady parents; while the man that is of a contrary nature should proceed to mate himself with one of the opposite kind. Regarding marriage as a whole there shall be one general rule: each man must seek to form such a marriage as shall benefit the State, rather than such as best pleases himself. There is a natural tendency for everyone to make for the mate that most resembles himself, whence it results that the whole State becomes ill-balanced