August Schleicher (1821-1868) is often credited with being the first scholar to apply a 'family tree' model to language groups, and with taking an evolutionist approach to language even before Darwin published On the Origin of Species. Schleicher had published extensively on individual European languages, notably the first formal description of Lithuanian, by the time his ground-breaking comparative Indo-European Compendium appeared in 1861-1862. This book was derived from his lectures, and was intended to save his students note-taking and copying from the blackboard. Each section begins with his reconstruction of a Proto-Indo-European phonological or morphological feature, and then shows how this is reflected in a range of daughter languages including Sanskrit, Greek, Latin, Avestan, Gothic, Lithuanian and Old Irish. A substantial appendix provides comparative paradigms, and there is a detailed table of contents in lieu of an index.
