Back in 2003, geneticist Peter Forster came out with some outlandish claims about Celtic languages. This work was later incorporated into Stephen Oppenheimer's equally outlandish Origins of the British.
If you were ever tempted to take Forster seriously, you should probably read this very thorough dismantling by linguist Larry Trask. Trask demonstrates to my satisfaction the paper is a "disaster" that is not worth paying attention to. Small sample:
The authors claim to be able to assign moderately reliable absoluteHow did the paper get published?
dates to branching events in their tree, and they do this, producing the astoundingly early dates given earlier.
But it is clear that they have merely re-invented glottochronology They claim that the rate of replacements is approximately constant -- a position known to be false.
. . . interestingly, PNAS is not peer-reviewed. Hmmm. This is not the first time that PNAS has published some extremely dubious work in historical linguistics.