Neanderthal theory of Indoeuropeans

The concept of Indoeuropeans emerged in the 16 century when European missionaries in Goa noticed that they understand some words of the local population. Many indirect facts indicate repeated migrations along the line connecting Spain and Sri Lanka. Officially, Indoeuropean languages are a separate family, just one of many, but is it true? Is human civilization a bush growing from many independent roots or a tree? In the latter case, Indoeuropeans have all chances to be its trunk.