There is in fact no evidence for the gradual progression of an entire material culture from the shores of the Black Sea to those of the Atlantic or t… - Jean-Paul Demoule

...there is only one solution left to save the invasionist model, or at least the concept of an “arrival of the Indo-Iranians”: invisible migrations. To this end, James Mallory, for example, came up with the military-inspired notion of Kulturkugel (“culture bullets”)—as if, perhaps, a Germanic term might excuse, almost in a humorous manner, the use of a diffusionist model by an English-speaking author. Mallory’s explanatory drawing shows a rifle cartridge (or a shell, depending) in which the bullet itself is the material culture and the charge is the language. Thus, the Indo-Aryan nomads of the steppes would have traveled across the BMAC, shedding their entire material culture on the way but not their language. Having thus become archaeologically undetectable, they would then have descended toward the Indus Plains to impose their new culture and their preserved language; this new culture would have had no known archaeological equivalent at the time.

The model of diffusion of “archaeological cultures,” each corresponding to a given “people,” is both naturalist and directly inspired by the nation states of the nineteenth century; it does not correspond to numerous situations provided, for example, by the ethnology of other continents or by the history and archaeology of protohistoric peoples of Early Medieval Europe.

While no one would dream of questioning the resemblances between the various so-called Indo-European languages, the centrifugal arborescent model in its current forms cannot be considered as validated due to the numerous contradictions that it contains. Furthermore, abuses, both past and present, of this model should incite us to the utmost rigor. We must therefore turn toward much more complex and multidisciplinary models concerning historical phenomena that span millennia if we are to meaningfully explore the multiplicity of problems that make up the “Indo-European question.”