This family tree is based on the majority Kurgan Theory of the origin of Proto-Indo European in the steppes of eastern Europe (present-day Belorus and The Ukraine). According to the Kurgan Theory, the first language that was distinctively Celtic would have developed in the third millennium BCE, perhaps around the middle reaches of the Danube: from what is now Slovakia and western Hungary across to Austria and the Czech Republic.
The early dates in the family tree are very tentative. Each stage of development would likely have been a dialect continuum rather than a single unitary language. Later dates, e.g. for Brythonic and Latin, both 2000 years ago, are chosen to show approximately when the language in question was most vigorous.
The family tree postulates Proto-Celto-Italic followed by a division into more northerly Proto-Celtic and more southerly Proto-Italic. This is one possible interpretation of the evidence, and it is convenient for diagrammatic purposes. Although the Kurgan Theory supposes that Proto-Celtic was part of a movement across Europe from east to west, there is also evidence for the influence of what may already have been a Celtic-speaking culture out of the Iberian Peninsula eastward across what is now France and the Low Countries.
There are several theories of when Celtic speakers arrived in the British Isles and how the 'Insular Celtic Languages' evolved. Scholarship increasingly supports an earlier arrival than was previously supposed (third/second rather than first millennium BCE), with the split into Goidelic and Brythonic languages occurring after arrival. Goidelic (now Irish, Scottish Gaelic, Manx) and Brythonic (now Welsh, Breton, Cornish) are distinguished by their different treatments of the Qw-sound inherited from Proto-Indo European: this became C in Goidelic but P in Brythonic. However, the Verb Subject word-order found in all Insular Celtic but not in the Celtic of continental Europe suggests there was a time when Insular Celtic was more-or-less a single tongue.
© 2012 / 2021 Ian Jackson