"As we have just mentioned, the people who emerge as the Tocharians in western sources are often equated with a branch of the Yuezhi of Chinese sources who were driven from the Gansu borderlands by the Xiongnu, then further west by the Wusun, arriving at the Oxus, and going on to conquesr Bactria and establish the Kushan empire. Narain argues that once one accepts the equation Tocharian = Yuezhi, then one is forced to follow both the Chinese historical sources (which for him would propel the Yuezhi back to at least the 7th century BC) and the geographical reference of their first cited historical location (Gansu) to the conclusion that they have lived there 'from time immemorial'. Narain infers that they had been there at least since the Qijia culture of c.200BC and probably even earlier in the Yangshao of the Neolothic. This would render the Tocharians as virtually native to Gansu (and earlier than the putative spread of the Neolithic to Xinjiang) and Narain goes so far as to argue that the Indo-Europeans themselves originally dispersed from this area westwards. Seldom has a tail so small wagged a dog so large."
I'm also reminded that David Chatters in his book Ancient Encounters (About Kennewick Man), speculated that Kennewick Man was on a branch of humanity that produced both todays Europeans and Asians.
See my post #116.