Their paper appears this week in Science.
The majority view in historical linguistics is that the homeland of Indo-European is located in the Pontic steppes (present day Ukraine) around 6,000 years ago. The evidence for this comes from linguistic paleontology: in particular, certain words to do with the technology of wheeled vehicles are arguably present across all the branches of the Indo-European family; and archaeology tells us that wheeled vehicles arose no earlier than this date. The minority view links the origins of Indo-European with the spread of farming from Anatolia 8,000 to 9,500 years ago.
Lexicons combined with dispersal of speakers
The minority view is decisively supported by the present analysis in this week's Science. This analysis combines a model of the evolution of the lexicons of individual languages with an explicit spatial model of the dispersal of the speakers of those languages. Known events in the past (the date of attestation dead languages, as well as events which can be fixed from archaeology or the historical record) are used to calibrate the inferred family tree against time.
Importance of phylogenetic trees
The lexical data used in this analysis come from the Indo-European Lexical Cognacy Database (IELex). This database has been developed in MPI's Evolutionary Processes in Language and Culture group, and provides a large, high-quality collection of language data suitable for phylogenetic analysis. Beyond the intrinsic interest of uncovering the history of language families and their speakers, phylogenetic trees are crucially important for understanding evolution and diversity in many human sciences, from syntax and semantics to social structure.
Science Daily. 2012. "Indo-European Languages Originated in Anatolia, Research Suggests". Science Daily. Posted: August 23, 2012. Available online: http://www.sciencedaily.com/releases/2012/08/120823175406.htm