While not necessarily accurate, studies in genetics and archaeology nevertheless present evidence that the migration of the Yamnaya people was rapid, and that it did not only involve new ideas spreading at a fast pace, but also individuals: Yamnaya men left a strong imprint on the European DNA.
New Scientist notes that Neolithic Europe was in crisis previous to the Yamnaya expansion. The assumption suggests that densely populated settlements were hit by plague-causing bacteria, which could have spread rapidly with the wheeled vehicles of the time. When the healthy, tall, and possibly violent Yamnaya arrived a few centuries later, they may have found little resistance in the indigenous population.
The full story can be read in the March 2019 issue of the New Scientist, and online for subscribers on the magazine website.