Commentary for Genesis 10:4

ובני יון, the Torah mentioned only a few of the families descended from the sons of Yaphet; we do not know why not all of them have been listed.

כתים ודודנים; elsewhere the דדנים are called רודנים. (Compare Chronicles I 1,7) This is to teach us that at times in history when the fortunes of the Jewish people as r ascending, these people treat us a “cousins,” in order to benefit from this biological relationship. When the fortunes of the Jewish people’s fortunes are on the decline, these “cousins,” are the first to join those who persecute us.

ודדנים, spelled with a double letter ד, whereas the same people are spelled as רודנים in Chronicles I 1,7. Seeing that the letters ד and ר look so similar to one another, it is quite possible that both spellings are used interchangeably. Someone may have mistaken the letter ד for the letter ר so that this error has been perpetuated. There can be no question that in a situation such as this, the spelling in the Torah must be considered authoritative, as Moses wrote at the dictation of G’d and with a high degree of prophetic insight. According to Josephus, the people concerned lived (in his time) along the river “Rodeno.”