Celtic Languages and computational phylogenetics: 88% of DNA in Ireland traces to ancestors who arrived in the Mesolithic period 81% in Wales

Yr Aflonyddwch Mawr had asked the question whether the work of Morris Swadesh has been applied to Celtic Languages and this lecture by Barry Cunliffe gives us our answer.

Statistical methods have been used in comparative linguistics since at least the 1950s with pioneering work of Morris Swadesh. 

Since about the year 2000,  interest in the topic, based on the application of methods of computational phylogenetics and cladistics to define an optimal tree (or network) to represent a hypothesis about the evolutionary ancestry and perhaps its language contacts.

The probability of relatedness of languages can be quantified and sometimes the proto-languages can be approximately dated.

The topic came to the attention of the popular press in 2003 after the publication of a short study on Indo-European in Nature (Gray and Atkinson 2003).

A volume of articles on Phylogenetic Methods and the Prehistory of Languages was published in 2006 as the result of a conference held in Cambridge in 2004.

In his 2006 book The Origins of the British (revised in 2007), Oppenheimer argued that neither Anglo-Saxons nor Celts had much impact on the genetics of the inhabitants of the British Isles, and that British ancestry mainly traces back to the Palaeolithic Iberian people, now represented best by Basques.

https://en.wikipedia.org/wiki/Stephen_Oppenheimer#Origins_of_the_British

88% of people in Ireland currently trace their roots back to people who first arrived after the ice age in the Mesolithic period (pre-Neolithic). 
That figure for Wales: 81%
Scotland: 70%
Cornwall: 79%
England: 68%