In the article, Carling & Cathcart use a database of features from 125 different languages of the Indo-European family, including extinct languages such as Sanskrit and Latin. Features include most of the differences that make the languages difficult to learn, such as differentiation in word order (thegirl throws the stonein English orcaitheann an cailín an chloch"throws the girl the stone" in Irish), gender (the applein English order Apfelin German), number of cases, number of forms of the verb, or whether languages have prepositions or postpositions (to the housein English butghar ko"house-to" in Hindi). With the aid of methods adopted from computational biology, the authors useknowngrammars to reconstruct grammars ofunknownprehistorical periods.

The reconstruction of Indo-European grammar has been the subject of lengthy discussion for over a century. In the 19^thcentury, scholars held the view that the ancient written languages, such as Classical Greek, were most similar to the reconstructed Proto-Indo-European language. The discovery of the archaic but highly dissimilar Hittite language in the early 20^thcentury shifted the focus. Instead, scholars believed that Proto-Indo-European was a language with a structure more similar to non-Indo-European languages of Eurasia such as Basque or languages of the Caucasus region.

The study confirms that Proto-Indo-European was similar to Classical Greek and Sanskrit, supporting the theory of the 19^thcentury scholars. However, the study also provides new insights into the mechanisms of language change. Some features of the proto-language were very stable and dominant over time. Moreover, features of higher prominence and frequency were less likely to change.

Though this study focused on one single family (Indo-European), the methods used in the paper can be applied to many other language families to reconstruct earlier states of languages and to observe how language evolves over time. The model also forms a basis for predicting future changes in language evolution.