Published online by Cambridge University Press: 31 July 2008
The surnames of all adult residents of five neighbouring communities in the fenlands of Cambridgeshire are compared with each other and with those of the 165,533 persons married in England and Wales in the period January to March 1975. Among the villages the average coefficient of relationship by isonymy (Ri) is 76 × 10−5. The villages nearer together may have a tendency to higher values of Ri: the correlation of Ri with the natural log of distance between villages is −0·49, p = 0·07. The surnames of the five villages give a weighted average Ri with the whole area about 25 miles of 54 × 10−5 and with a zone 25–40 miles away of 45 × 10−5, whereas Ri with all England and Wales is 42 × 10−5. Rare surnames show a much sharper gradient and contribute approximately twice as much to the coefficient in the 25–40 mile zone and six times as much within 25 miles as found with all England and Wales. Moderately frequent surnames and even common surnames show the same gradient, but to a lesser degree. In the part of Cambridgeshire studied, the present distribution of surnames indicates a slight but appreciable local isolation, with the degree of relationship decreasing from among local villages to that between the villages and all England and Wales. This pattern is consistent with the theory of genetic inbreeding based on distance but there is considerable variability in individual instances.