"...the Yuezhi (Yüeh-chih in Wade-Giles), an Indo-European-speaking nomadic people who had relocated from China's present-day Gansu Province as a result of their earlier defeat by the Xiongnu."
There is the Gansu area and Indo-European speaking people again.
The Yue-chih or Tocharians are a very interesting group of people. Pity we don't know more about them. The thing that interests me is that we can broadly classify humanity into 3 races: Caucasoid, Negroid and Mongoloid. The Caucasoids are the most numerous --2.5 billion, the Mongoloids next with 1.5 billion and Afroids with 1 billion, the rest being mixtures of these three (of course, really speaking I'd say nearly ALL of us are mixtures, but the 1 billion are what you might call apparent mixtures like the South East Asians who are a Caucasoid-Mongoloid mix. if we look at genome diversity, the greatest diversity is shown amongst Negroids but the greatest color and feature difference is found amongst Caucasoids. Maybe it's because hte Caucasoids had a vast range of territory -- bordered by the Sahara and the Gobi-Siberian deserts