Sentence:  The entire human and most of the animal and vegetable genetic stock now found in Britain and Ireland arrived (and continues to arrive) over the last 12,000 years. That fact alone, it is suggested, offers a new "longue duree" (or ‘<WSD>timescape</WSD>') for population history. 
Meaning of the word marked with <WSD> tags:  A perspective over a period (particularly a long period) of time.