On linguistic and genetic uncertainty

I’ve been reading The Origins of the British: The New Prehistory of Britain by Stephen Oppenheimer, in Kindle, and ran across a comment that may pertain to something someone said a while back – I only recall the strangeness of the comment, something along the lines of a statement or an argument must mean one thing and one thing only.  No doubt I misunderstood the context (now that I think more about it, I suspect the context may have had to do with philosophy and not linguistics), but I believe the opposite of that, that almost everything is ambiguous and probably means something different to everyone who reads or hears it – not utterly different in most cases, but marginally so, that is “not quite what the speaker intended.” 

Oppenheimer in location 1656 writes, “There are basic differences between the disciplines of archaeology and linguistics on the one hand, and sciences such as geology and biology on the other.  In their attitude to the scientific method, some linguists seem to misunderstand the meaning or, or are unable to accept, uncertainty.  They interpret the scientific method as implying authority, rigour and certainty, while scientists accept that, in many situations, comparisons have to be made using measurements that have some degree of error and theories of classification with a degree of uncertainty.  A statistical approach has to be used to handle such uncertainty.  Unlike disagreements between academic authorities, there are standard methods of dealing with sources of observational error and of uncertainty.  Archaeologists, in contrast to linguists, have learnt through experience that if a method such as carbon dating gives inaccurate results at first, it should not be thrown out of the window, but attempts should be made to sort out the problems of error and improve it. 

Comment:  The context of Oppenheimer’s comment was in regard to dating celtic-language splits.  The mathematical approach to language diversity is called lexico-statistics and the dating method glottochronology, and as one might suspect disagreements amongst the archeologists, linguists, geneticists, and geologists are rife. 

I was hoping for a bit more certainty than I’ve found in Oppenheimer thus far.  I mentioned some place that I had my DNA checked on Ancestry.com a couple of years ago.  Interestingly, though a DNA check sounds scientific; my results have changed over time.  Instead of something like 60% British Isles and 20% Scandinavian (probably from the Viking colonies in Britain) I am now something like 60% Western European and 20% Irish.  No Irish has ever been mentioned or seen in my family tree (begun by one of my grandfathers). 

In the Ancestry.com definitions, one can find British (which I find in my genealogic tree) under Western Europe and Scottish (also in my genealogic tree) under Irish.  And that ambiguity can be found in recent studies such as Oppenheimer’s; so perhaps the Ancestry people are updating results as new arguments are advanced.  There is no consensus on the reasons for the difference between the Scots and the Irish, for example, or whether they originally came from central Europe as many have believed or through Southern France and Spain as Oppenheimer and later scholars now believe. 

Having read Collingwood and Gadamer I am used to and accepting of ambiguity in written and spoken language, but like the linguists Oppenheimer complains of I have difficulty with so much ambiguity in (primarily) genetics.