The whole of Western China was peopled by an Iranian people called Saka. One of their branches was the Tokarian that had a developed culture (pic) and spoke an Arian language similar to the Persian. Yet from the Tenth Century AD they lost to competing Turkish tribes and disappeared. The only remnant are the Uyghurs, that are thoroughly mixed and look Asian. Only a few of them have clear eyes and semi-European features.
In the vast space of Central Asia where the Iranian race encountered the Turkish/Chinese race, the result was a steady advance of the Asians toward the West, encroaching on Iranian lands, a progress that only stopped on the Mediterranean coast. The Iranians have been retreating for a millennium, even their central homeland on the Iranian plateau is being colonized by Azeri Turks.
The Iranians have much to offer to humanity, it should be a pity if they were to follow their brothers the Saka of China.