Judging from the comment about lactose tolerance in Austria/Slovakia/Hungary, they may be relying on a paper that came out of Mark Thomas's lab last year: "The Origins of Lactase Persistence in Europe".John Hawks agrees:
The authors of that paper tried to estimate the region of origin using simulations - but one of the inputs was the current distribution of that allele. Which is reasonable, except that they did not use the actual distribution of that allele, but rather a truncated distribution - their map is centered on central Europe and stops halfway through the Ukraine. That ensured that they would find an origin in somewhere in middleuropa.
The allele doesn't stop there, though: it has a second region of fairly high frequency in northern India. Before Mongols and Turks took over the Eurasian steppe, the frequency of that allele may have been high in those steppe regions. Scythians are described as milk-drinkers quite a while ago - in the Iliad. And my sources claim that the royal guard of the Hittites also 'drank sweet milk'...
Checking out ancient DNA from Kurgan burials in that region might clarify this.
I think it is difficult to imagine a historical process that moves a lot of people from Bavaria to the Punjab: it is easier to imagine one that expands to both regions from somewhere in-between.
Which would explain the distribution of the Indo-European languages, also.
When you think about it, it may not be easy for German researchers to talk about this hypothesis. I think they have trouble saying "Aryan" nowadays.
Problem is: from the standpoint of ancient DNA samples, the lactase persistence mutation was also absent within the early Neolithic! The article is full of details that are wrong or misleading. [. . .]
The [mtDNA] differences between early Neolithic and later Europeans suggests that post-Neolithic migrations -- real Völkerwandurung -- actually had a major impact on the European gene pool. What we see today is not a pattern established 6000 years ago, but a palimpsest richly painted with strokes from successive migrations.
One aspect of this scenario: There's no reason to link the early Neolithic with Indo-European languages. There were many later widespread population movements that might have carried this language family, and we know that these later movements were genetically decisive -- at least, as concerns the maternal genealogy. The relation of Y chromosome haplogroups with mtDNA haplogroups is a critical question, but even more necessary is the development of an effective means of testing these hypotheses with nuclear genotype data.