I got it from the book The Tarim Mummies, by JP Malloy and Victor Mair. They were quoting from the work of an Indian archaeologist named Narain, who said, that Indo-Europeans originated in the Gansu region of China.
I'm beginning to think they originated somewhere around Sundaland and migrated up the river valleys of China at the end of the Ice Age...some also probably went/came by boat. They were probably the original Sumerians.
When Sundaland went underwater, they spread out all over the world taking their megalithic and pyramid building custom with them. Relatives of Kennewick Man, Spirit Cave Man, etc.
Also, I've been toying with another idea. It is that the red-headed mummies of the Tarim Basin are distantly related to the Celts of Hallstadt, Austria, a distance of 4-5,000 miles. Mair can't explain the close similatities of these people when there are no archaeological or linguistic traces of a migration between these two points. My idea: The Austrian Celts came by boat and the Tarim Basin group migrated over land from the Sundaland region.
Here's the actual qoute from the book, The Tarim Mummies
"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.2000BC 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."