"Ancestry-constrained phylogenetic analysis supports the Indo-European steppe hypothesis", by Will Chang, Chundra Cathcart, David Hall and Andrew Garrett, will appear in the March issue of the academic journal Language. A pre-print version of the article is freely available from the Linguistic Society of America, the publishers of Language:
This article provides new support for the "steppe hypothesis" or "Kurgan hypothesis", which proposes that Indo-European languages first spread with cultural developments in animal husbandry around 4500 - 3500 BCE. (An alternate theory proposes that they diffused much earlier, around 7500 - 6000 BCE, in Anatolia in modern-day Turkey.)
Chang et al. examined over 200 sets of words from living and dead Indo-European languages; after determining how quickly these words changed over time through statistical modeling, they concluded that the rate of change indicated that the languages which first used these words began to diverge approximately 6,500 years ago, in accordance with the steppe hypothesis.
This is one of the first quantitatively-based academic papers in support of the steppe hypothesis, and the first to use a model with "ancestry constraints" which more directly incorporate previously discovered relationships between languages. In future research, methods from this study could be used to study the origins of other language families, such as Afro-Asiatic and Sino-Tibetan.
EurekAlert. 2015. “New insights into origins of the world's languages”. EurekAlert. Posted: February 18, 2015. Available online: http://www.eurekalert.org/pub_releases/2015-02/lsoa-nii021815.php