Isonymic analysis of population structure in Gredos, Spain.

For the period 1875-1975 an isonymic analysis was made based on 41,696 marriages celebrated in three valleys (Tormes, Alberche and Tietar) from Gredos (Spain). Total inbreeding (Ft) was lower in the Tietar valley (0.0103- 0.0136), followed by the Tormes (0.0125-0.0255) and the Alberche (0.0153-0.0200). In the latter, random inbreeding (Fr) surpassed non random (Fn). Correlation coefficients were obtained to confirm an association of inbreeding from isonymy with valley and village endogamy rates, locality census, altitude, and alpha inbreeding. Fn correlated positively with average valley endogamy and village endogamy and with altitude, but inversely with census size. Contrarily, Fr related significantly to village endogamy. The non-random component from isonymy related positively to inbreeding from dispensations. Except for village endogamy, both variables show the same relationships to variables, such as altitude, which reflect limitations to mobility; or valley endogamy indicating the disposability of potential mates which in turn depends on the census size.