What ? i dont think Herodutus has said that Scythians came from South, meaning Iran. He said they came from beyond a river ( surely the Volga ) and pushed the Cimmerians to migrate into the Middle-East, where they purchase them for a time. Here Cimmerians became mercenaries for Mesopotamians rulers and put an end to the Phrygian Kingdom some times later, before disappear from history. Never eard anything about proper scythians coming from south. Massagaetes, that are believe to be scythians-related where put somewhere near the Amou-Darya and Syr-Darya. But in all greek mentions of Scythians they are localised in the pontic steppe.
Edit: I just saw that statement in Wikipedia:
- Thirdly (4.11), in the version which Herodotus said he believed most, the Scythians came from a more southern part of Central Asia, until a war with the Massagetae (a powerful tribe of steppe nomads who lived just northeast of Persia) forced them westward.
There is yet another story, to which account I myself especially incline. It is to this effect. The nomadic Scythians inhabiting Asia, when hard pressed in war by the Massagetae, fled across the Araxes1 river to the Cimmerian country (for the country which the Scythians now inhabit is said to have belonged to the Cimmerians before), [2] and the Cimmerians, at the advance of the Scythians, deliberated as men threatened by a great force should. Opinions were divided; both were strongly held, but that of the princes was the more honorable; for the people believed that their part was to withdraw and that there was no need to risk their lives for the dust of the earth; but the princes were for fighting to defend their country against the attackers. [3] Neither side could persuade the other, neither the people the princes nor the princes the people; the one party planned to depart without fighting and leave the country to their enemies, but the princes were determined to lie dead in their own country and not to flee with the people, for they considered how happy their situation had been and what ills were likely to come upon them if they fled from their native land. [4] Having made up their minds, the princes separated into two equal bands and fought with each other until they were all killed by each other's hands; then the Cimmerian people buried them by the Tyras river, where their tombs are still to be seen, and having buried them left the land; and the Scythians came and took possession of the country left empty.
1 Herodotus' idea of the course of this river is uncertain; cp. Hdt. 1.202. He appears to extend the Araxes, which flowed from the west into the Caspian, into regions east of that sea.
Looks more like Historians have deliberatly place that South Central Asia reference, because of where they believe that Massagaetes historical territory was. There is no mention of Herodotus of a proper Southern origin.