Anah, the Mules, and a Tainted Line in Seir

Rabban Shimon ben Gamliel says: There was a mule already in the days of Anah, as it is said, "This is Anah who found the yemim [mules] in the wilderness" (Genesis 36:24). The expounders of difficult matters say: Anah himself was of unfit birth, and he brought unfitness into the world. For it is said, "These are the sons of Seir the Horite, the inhabitants of the land: Lotan and Shoval and Tzivon and Anah" (Genesis 36:20), and it is written, "And these are the sons of Tzivon: both Aiah and Anah; this is the Anah" (Genesis 36:24) and so on. This teaches that Tzivon came in upon his own mother and fathered Anah from her [so that Anah was at once Tzivon's son and his brother]. But perhaps there were two men named Anah? [No,] "this is the Anah" [means] the Anah from the very start [the same one named earlier].