Jasper Griffiths in the Oxford History of the Classical World quotes this passage to show how archaic customs were preserved in myths but which later were only to be found among barbarians.
προσθετέον δ᾽ ἡμῖν τοῖς εἰρημένοις ὅτι μετὰ τὴν ἀποθέωσιν αὐτοῦ Ζεὺς Ἥραν μὲν ἔπεισεν υἱοποιήσασθαι τὸν Ἡρακλέα καὶ τὸ λοιπὸν εἰς τὸν ἅπαντα χρόνον μητρὸς εὔνοιαν παρέχεσθαι, τὴν δὲ τέκνωσιν γενέσθαι φασὶ τοιαύτην: τὴν Ἥραν ἀναβᾶσαν ἐπὶ κλίνην καὶ τὸν Ἡρακλέα προσλαβομένην πρὸς τὸ σῶμα διὰ τῶν ἐνδυμάτων ἀφεῖναι πρὸς τὴν γῆν, μιμουμένην τὴν ἀληθινὴν γένεσιν: ὅπερ μέχρι τοῦ νῦν ποιεῖν τοὺς βαρβάρους ὅταν θετὸν υἱὸν ποιεῖσθαι βούλωνται.
Diodorus Siculus . 4.39.2
We should add to what we have just said that after Hercules had been made into a god, Zeus persuaded Hera to adopt him as a son and to give him her maternal love in the future for all time. They say the adoption was like this. Hera got onto her bed and clasping Hercules next to her body let him down onto the ground through her clothes, copying a real birth. Something which up to the present day barbarians do when they want to adopt a son.